Introduction
Cervical cancer (CC) remains a major public health challenge globally, particularly in low- and lower-middle-income countries (LLMICs), where nearly 90% of CC-related deaths occur.1 In Bangladesh, CC is the second most common cancer among women, with approximately 9,640 new cases and more than 5,826 deaths annually.2 The burden is especially high among women in low-resource urban and rural settings, highlighting the urgent need for effective prevention strategies.3 Persistent infection with high-risk human papillomavirus (HPV), especially types 16 and 18, accounts for 70â80% of all CC cases worldwide.4,5 Preventive vaccination against HPV has shown remarkable success in reducing HPV infection and subsequent cervical precancerous lesions.6 The bivalent HPV vaccine (targeting types 16 and 18) induces robust immune responses and has demonstrated effectiveness in both high-income and resource-constrained settings.7,8 In Tanzania, single-dose bivalent HPV vaccination has shown high seropositivity among adolescent girls at 24 months.9
Recognizing the critical role of HPV vaccination in CC prevention, the World Health Organization (WHO) launched a global strategy in November 2020 to eliminate CC as a public health problem. One key target is to ensure that 90% of girls are fully vaccinated with the HPV vaccine by the age of 15 by the year 2030.10 Although both bivalent and quadrivalent vaccines have been recommended, their adoption into national immunization programs has been limited in many LLMICs, including Bangladesh. Challenges such as the high cost of vaccines, the need for multiple doses, and logistical constraints have hindered widespread implementation.11
Recent studies have demonstrated that a single dose of the bivalent HPV vaccine can provide durable immunogenicity comparable to multi-dose regimens. A landmark study in Costa Rica found that over 90% of women remained seropositive for HPV16 and 18 even 11 years after a single dose, with stable antibody levels throughout the follow-up period.12 Evidence from cohort studies, randomized trials, and systematic reviews from India, Kenya, and other regions further supports the protective efficacy and durable immunogenicity of single-dose HPV vaccination.13â15
The cost of the HPV vaccine and the necessity of a multidose schedule are significant barriers to HPV vaccine introduction and sustainability in many LLMICs. The cost of vaccine procurement and delivery has been a major obstacle to the governmentâs commitment to national HPV vaccine introduction.16,17 Additionally, the global HPV vaccine shortage has become a barrier to the introduction and expansion of national HPV programs in some countries.18 Therefore, implementing a single-dose schedule would aid the effective elimination of CC by reducing vaccine costs and simplifying program logistics, including supply, delivery, and accessibility in LLMICs. Evidence supports the immunogenicity and protective effectiveness of a single-dose regimen against HPV-related outcomes.19â21 For countries like Bangladesh, a single-dose regimen presents an opportunity to simplify vaccine delivery, reduce program costs, and overcome logistical barriers, making nationwide implementation more feasible and sustainable. These factors indicate the necessity of introducing a single-dose regimen to increase coverage of girls in the target age group to achieve the WHO global elimination target in Bangladesh. In November 2019, the National Center for Cervical and Breast Cancer Screening and Training (NCCBCST), Bangladesh Medical University (BMU), conducted an HPV vaccination program at NCCBCST and selected vaccination sites in Dhaka. Participants were engaged through advocacy meetings, provided with essential information, and their ages were verified via birth certificates. Teachers organized the events and supported the participants, while staff of the Expanded Program on Immunization (EPI) administered the vaccines free of charge, maintaining proper cold chain standards. Post-vaccination, the girls were observed for 30 minutes for adverse effects. A total of 970 girls received a single dose of the bivalent HPV vaccine. This study aimed to evaluate the seroprevalence following a single-dose bivalent HPV vaccine among adolescent girls in Bangladesh and to explore its association with sociodemographic characteristics.
Materials and methods
Study design and setting
This was a cross-sectional, follow-up seroprevalence study conducted between January 1 and June 30, 2023, at the NCCBCST, BMU, Dhaka, Bangladesh. The objective was to assess the seroprevalence of HPV types 16 and 18 antibodies in adolescent girls at follow-up after receiving a single dose of the bivalent HPV vaccine. In November 2019, an HPV vaccination campaign was implemented by NCCBCST in collaboration with the EPI, Bangladesh. The campaign targeted girls aged nine to fifteen years from ten purposively selected vaccination sites across Dhaka (Table 1). These sites were selected to provide broad geographic representation of Dhaka city. A single dose of the bivalent HPV vaccine (Cervarix®, GlaxoSmithKline) was administered, and health education sessions on HPV and CC prevention were conducted. A total of 970 girls were vaccinated during this initiative, serving as the cohort for the present follow-up study.
Table 1Distribution of study participants according to selected vaccination/recruitment sites
| Vaccination/recruitment site | Initially vaccinated | Recruited at follow up for seroprevalence |
|---|
| Begum Rahima Adarsha School | 45 | 36 |
| Uttarkhan Collegiate School | 176 | 130 |
| Monija Rahaman Girls School | 122 | 91 |
| Diabari Primary School | 51 | 39 |
| Bailjhuri School | 60 | 42 |
| Shotodol School | 105 | 72 |
| Rowshan Ara Uchya Bidyaloy | 170 | 120 |
| Shere Bangla Girls School | 130 | 88 |
| Nagar Matri Sadan Nagar Health Center | 41 | 30 |
| Kamrangirchar 31 Bed Hospital | 70 | 20 |
| Total | 970 | 648 |
Study population and recruitment
The target population consisted of 970 adolescent girls aged nine to fifteen years at the time of vaccination. For the follow-up, all vaccinated individuals were contacted through phone calls, community outreach, and written invitations facilitated by school authorities. Inclusion criteria for the follow-up study were: (1) receipt of a single dose of the bivalent HPV vaccine during the 2019 campaign; (2) current residence in Dhaka or surrounding areas; and (3) provision of written informed consent from a parent or guardian, along with assent from the participant. Participants were excluded if they had a known history of HPV infection or cervical lesions; had received any prior HPV vaccination before the study; were immunocompromised or had chronic illnesses that could interfere with immune response (e.g., HIV/AIDS, cancer); had serious illness at the time of enrollment; declined to provide informed consent/assent; or were unwilling to provide a blood sample.
Blood sample collection and storage
Venous blood (5 mL) was collected from each participant by trained medical technologists and nurses using standard aseptic techniques. All samples were transported to the laboratory at the Department of Virology, BMU, while maintaining the cold chain. Blood samples were centrifuged at 3,000 rpm for 10 min to separate the serum. The separated serum was aliquoted into sterile cryovials and stored at â80°C until laboratory analysis. All procedures adhered to national biosafety standards and quality assurance protocols.
Laboratory analysis: detection of HPV-specific antibodies
To assess the presence of type-specific immunoglobulin G (IgG) antibodies against HPV types 16 and 18, serum samples were tested using a commercial enzyme-linked immunosorbent assay kit (CUSABIO Technology LLC, USA; Catalog No. CSB-EQ027477HU for HPV16 L1 IgG and CSB-EQ027476HU for HPV18 L1 IgG) designed to detect antibodies against the HPV L1 capsid protein. The enzyme-linked immunosorbent assay plates were pre-coated with HPV16 or HPV18 antigens. A 100 µL aliquot of each participantâs serum was added to the wells and incubated according to the manufacturerâs instructions. Following incubation, wells were washed and incubated with anti-human IgG conjugated with horseradish peroxidase. A chromogenic substrate was then added, resulting in color development proportional to the amount of bound antibody. Optical density was measured at 450 nm using a calibrated microplate reader. Serostatus was classified using a cutoff value of 2.1. All assays were conducted in duplicate and included appropriate positive and negative controls to ensure assay reliability and reproducibility. All laboratory analyses were conducted at the Department of Virology, BMU, maintaining rigorous quality control measures throughout the testing process.
Data collection and variables
Sociodemographic and vaccination history data were collected through a structured questionnaire administered during the follow-up visit. Variables recorded included age group, participantâs education level, motherâs education, motherâs occupation (homemaker or employed), fatherâs education, fatherâs occupation, and household monthly income categorized in Bangladeshi Taka (BDT) as up to 10,000, 10,001â20,000, 20,001â50,000, and 50,001 or above.
Statistical analysis
Sample size justification
This study aimed to follow up the entire cohort of 970 adolescent girls who received a single dose of the bivalent HPV vaccine in 2019. However, due to logistical and practical constraints, including participant availability, informed consent, and eligibility, a total of 648 girls were ultimately enrolled in the follow-up seroprevalence assessment, representing approximately 67% of the original vaccinated cohort. Based on an expected seroprevalence of 90%, a 5% margin of error, and a 95% confidence level, the minimum required sample size was calculated to be 122 participants. The achieved sample size of 648 exceeded this reported requirement. However, 322 of the 970 vaccinated girls (33.2%) were not included in the follow-up analysis, and purposive selection of the study sites may have introduced non-response and selection bias, limiting generalizability.
Data analysis
Data were entered into Microsoft Excel and analyzed using IBM SPSS Statistics version 26.0. Descriptive statistics, including frequencies and percentages, were used for categorical variables, and means with standard deviations were calculated for continuous variables. Bivariate associations between HPV antibody seropositivity (for HPV 16 and HPV 18) and participant characteristics were evaluated using chi-square (Ï2) tests. To explore factors associated with seropositivity, two separate binary logistic regression models were developed, one for HPV 16 and another for HPV 18. In the reported models, the dependent variable was serostatus (positive or negative), and independent variables included participantsâ age group, education level, motherâs education, motherâs occupation, fatherâs education, fatherâs occupation, and monthly family income. Adjusted odds ratios (aORs) with 95% confidence intervals (CIs) were reported, and statistical significance was defined as a p-value less than 0.05.
Ethical considerations
Ethical clearance was obtained from the Institutional Review Board of BMU Ethics and Scientific Review Committee (Ref: No BSMMU/2020/686, dated 16/01/2020). This study was conducted in accordance with the Declaration of Helsinki. Written informed consent was obtained from parents/guardians, and assent was obtained from participants.
Results
A total of 970 adolescent girls received a single dose of the bivalent HPV vaccine during a campaign in November 2019. All vaccinated girls were invited to participate in a follow-up seroprevalence study in 2023. Of these, 648 girls were available, met the eligibility criteria, and provided informed consent, forming the final study sample (Fig. 1).
Sociodemographic characteristics of the participants
The reported age distribution comprised 82.4% in the nine-to-thirteen-year category, with a mean of 11.89 ± 1.59 years; whether these ages refer to vaccination or follow-up is not specified consistently. Most were enrolled in grades three to eight, with 39.2% in grades three to five and 49.7% in grades six to eight. Regarding maternal education, 63.6% of mothers had education up to the primary level, while only 6.2% had completed graduate-level or higher education. The vast majority of mothers were housewives (97.1%), and the predominant paternal occupation was business (44.3%), followed by private jobs (23.5%) and government jobs (12.8%). Over half of the participants (52.3%) came from households with a monthly income of up to BDT 10,000, indicating a largely low-income population (Table 2).
Table 2Distribution of sociodemographic characteristics of the participants (N = 648)
| Characteristics | Frequency | Percentage |
|---|
| Reported participantsâ age (years) | | |
| ââ9â13 | 534 | 82.4 |
| ââ14â15 | 114 | 17.6 |
| ââMean ± SD | 11.89±1.59 | |
| Participantsâ educational qualification | | |
| ââGrades 3â5 | 254 | 39.2 |
| ââGrades 6â8 | 322 | 49.7 |
| ââGrades 9â10 | 72 | 11.1 |
| Mothersâ educational qualification | | |
| ââNo schooling | 19 | 2.9 |
| ââUp to primary | 412 | 63.6 |
| ââSSC | 123 | 19.0 |
| ââHSC | 54 | 8.3 |
| ââGraduate and above | 40 | 6.2 |
| Mothersâ occupation | | |
| ââHousewife | 629 | 97.1 |
| ââService holder | 19 | 2.9 |
| Fathersâ educational qualification | | |
| ââNo schooling | 27 | 4.2 |
| ââUp to primary | 381 | 58.8 |
| ââSSC | 107 | 16.5 |
| ââHSC | 59 | 9.1 |
| ââGraduate and above | 74 | 11.4 |
| Fathersâ occupation | | |
| ââFarming | 71 | 11.0 |
| ââGovernment job | 83 | 12.8 |
| ââPrivate job | 152 | 23.5 |
| ââBusiness | 287 | 44.3 |
| ââLiving abroad | 41 | 6.3 |
| ââDriver | 14 | 2.2 |
| Monthly income | | |
| ââUp to Taka 10,000 | 339 | 52.3 |
| ââTaka 10,001â20,000 | 219 | 33.8 |
| ââTaka 20,001â50,000 | 78 | 12.0 |
| ââTaka 50,001 and above | 12 | 1.9 |
Seroprevalence of HPV antibodies
At follow-up in 2023, the reported overall seroprevalence was 72.8% for HPV type 16 antibodies and 82.4% for HPV type 18 antibodies (Fig. 2).
HPV 16 antibody seropositivity
Reported HPV16 antibody seropositivity was 75.1% in the nine-to-thirteen-year age category and 62.3% in the 14â15-year category. Girls in grades three to five had a reported prevalence of 75.6%, compared with 61.1% in grades nine to ten. Reported prevalence ranged from 57.9% among girls whose mothers had no formal education to 83.3% among those whose mothers had HSC-level education. These subgroup comparisons are descriptive and should be interpreted cautiously (Table 3).
Table 3Relationship between HPV 16 antibodies and characteristics of the participants
| Characteristics | HPV 16 antibody
| Total N (%) | Reported p-value |
|---|
| Positive N (%) | Negative N (%) |
|---|
| Age group (years) | | | | |
| ââ9â13 | 401 (75.1) | 133 (24.9) | 534 (100.0) | 0.005 |
| ââ14â15 | 71 (62.3) | 43 (37.7) | 114 (100.0) | |
| ââTotal | 472 (72.8) | 176 (27.2) | 648 (100.0) | |
| Participantsâ educational qualification | | | | |
| ââGrades 3â5 | 192 (75.59) | 62 (24.41) | 254 (100) | 0.050 |
| ââGrades 6â8 | 236 (73.29) | 86 (26.71) | 322 (100) | |
| ââGrades 9â10 | 44 (61.11) | 28 (38.89) | 72 (100) | |
| ââTotal | 472 (72.8) | 176 (27.2) | 648 (100) | |
| Mothersâ educational qualification | | | | |
| ââNo schooling | 11 (57.9) | 8 (42.1) | 19 (100) | 0.085 |
| ââUp to primary | 290 (70.4) | 122 (29.6) | 412 (100) | |
| ââSSC | 96 (78.0) | 27 (22.0) | 123 (100) | |
| ââHSC | 45 (83.3) | 9 (16.7) | 54 (100) | |
| ââGraduate and above | 30 (75.0) | 10 (25.0) | 40 (100) | |
| ââTotal | 472 (72.8) | 176 (27.2) | 648 (100) | |
| Mothersâ occupation | | | | |
| ââHousewife | 458 (72.8) | 171 (27.2) | 629 (100) | 0.933 |
| ââService holder | 14 (73.7) | 5 (26.3) | 19 (100) | |
| ââTotal | 472 (72.8) | 176 (27.2) | 648 (100) | |
| Fathersâ educational qualification | | | | |
| ââNo schooling | 19 (70.37) | 8 (29.63) | 27 (100.00) | 0.074 |
| ââUp to primary | 267 (70.08) | 114 (29.92) | 381 (100.00) | |
| ââSSC | 83 (77.57) | 24 (22.43) | 107 (100.00) | |
| ââHSC | 51 (86.44) | 8 (13.56) | 59 (100.00) | |
| ââGraduate and above | 52 (70.27) | 22 (29.73) | 74 (100.00) | |
| ââTotal | 472 (72.8) | 176 (27.2) | 648 (100.00) | |
| Fathersâ occupation | | | | |
| ââFarming | 42 (59.15) | 29 (40.85) | 71 (100.00) | 0.093 |
| ââGovernment job | 63 (75.90) | 20 (24.10) | 83 (100.00) | |
| ââPrivate job | 108 (71.05) | 44 (28.95) | 152 (100.00) | |
| ââBusiness | 215 (74.91) | 72 (25.09) | 287 (100.00) | |
| ââLiving abroad | 33 (80.49) | 8 (19.51) | 41 (100.00) | |
| ââDriver | 11 (78.57) | 3 (21.43) | 14 (100.00) | |
| ââTotal | 472 (72.8) | 176 (27.2) | 648 (100.00) | |
| Monthly income | | | | |
| ââUp to Taka 10,000 | 255 (75.22) | 84 (24.78) | 339 (100) | 0.491 |
| ââTaka 10,001â20,000 | 155 (70.78) | 64 (29.22) | 219 (100) | |
| ââTaka 20,001â50,000 | 53 (67.95) | 25 (32.05) | 78 (100) | |
| ââTaka 50,001 and above | 9 (75.0) | 3 (25.0) | 12 (100) | |
| ââTotal | 472 (72.8) | 176 (27.2) | 648 (100) | |
HPV 18 antibody seropositivity
Reported HPV18 antibody seropositivity was 82.8% in the nine-to-thirteen-year age category and 80.7% in the 14â15-year category. The reported prevalence was 92.6% among daughters of mothers with HSC-level education. Across household income groups, the reported prevalence was highest at up to BDT 10,000 (88.8%) and lowest at BDT 20,001â50,000 (67.9%). These comparisons should be interpreted cautiously (Table 4).
Table 4Relationship between HPV 18 antibodies and characteristics of the participants
| Characteristics | HPV 18 antibody
| Total N (%) | Reported p-value |
|---|
| Positive N (%) | Negative N (%) |
|---|
| Age group (years) | | | | |
| ââ9â13 | 442 (82.8) | 92 (17.2) | 534 (100.0) | 0.598 |
| ââ14â15 | 92 (80.7) | 22 (19.3) | 114 (100.0) | |
| ââTotal | 534 (82.4) | 114 (17.6) | 648 (100.0) | |
| Participantsâ educational qualification | | | | |
| ââGrades 3â5 | 212 (83.46) | 42 (16.54) | 254 (100) | 0.698 |
| ââGrades 6â8 | 265 (82.30) | 57 (17.70) | 322 (100) | |
| ââGrades 9â10 | 57 (79.17) | 15 (20.83) | 72 (100) | |
| ââTotal | 534 (82.4) | 114 (17.6) | 648 (100) | |
| Mothersâ educational qualification | | | | |
| ââNo schooling | 15 (78.9) | 4 (21.1) | 19 (100) | 0.249 |
| ââUp to primary | 335 (81.3) | 77 (18.7) | 412 (100) | |
| ââSSC | 99 (80.5) | 24 (19.5) | 123 (100) | |
| ââHSC | 50 (92.6) | 4 (7.4) | 54 (100) | |
| ââGraduate and above | 35 (87.5) | 5 (12.5) | 40 (100) | |
| ââTotal | 534 (82.4) | 114 (17.6) | 648 (100) | |
| Mothersâ occupation | | | | |
| ââHousewife | 519 (82.5) | 110 (17.5) | 629 (100) | 0.688 |
| ââService holder | 15 (78.95) | 4 (21.05) | 19 (100) | |
| ââTotal | 534 (82.4) | 114 (17.6) | 648 (100) | |
| Fathersâ educational qualification | | | | |
| ââNo schooling | 20 (74.07) | 7 (25.93) | 27 (100) | 0.074 |
| ââUp to primary | 307 (80.58) | 74 (19.42) | 381 (100) | |
| ââSSC | 87 (81.31) | 20 (18.69) | 107 (100) | |
| ââHSC | 55 (93.22) | 4 (6.78) | 59 (100) | |
| ââGraduate and above | 65 (87.84) | 9 (12.16) | 74 (100) | |
| ââTotal | 534 (82.41) | 114 (17.59) | 648 (100) | |
| Fathersâ occupation | | | | |
| ââFarming | 55 (77.46) | 16 (22.54) | 71 (100) | 0.789 |
| ââGovernment job | 69 (83.13) | 14 (16.87) | 83 (100) | |
| ââPrivate job | 124 (81.58) | 28 (18.42) | 152 (100) | |
| ââBusiness | 239 (83.28) | 48 (16.72) | 287 (100) | |
| ââLiving abroad | 36 (87.80) | 5 (12.20) | 41 (100) | |
| ââDriver | 11 (78.57) | 3 (21.43) | 14 (100) | |
| ââTotal | 534 (82.41) | 114 (17.59) | 648 (100) | |
| Monthly income | | | | |
| ââUp to Taka 10,000 | 301 (88.79) | 38 (11.21) | 339 (100) | <0.001 |
| ââTaka 10,001â20,000 | 170 (77.63) | 49 (22.37) | 219 (100) | |
| ââTaka 20,001â50,000 | 53 (67.9) | 25 (32.1) | 78 (100) | |
| ââTaka 50,001 and above | 10 (83.33) | 2 (16.67) | 12 (100) | |
| ââTotal | 534 (82.4) | 114 (17.6) | 648 (100) | |
Factors associated with HPV 16 antibody seropositivity
In the reported exploratory multivariable analysis, the adjusted odds ratio for HPV16 seropositivity was 0.61 (95% CI: 0.39â0.95) for the 14â15-year age category compared with the nine-to-thirteen-year category, and 0.50 (95% CI: 0.28â0.89) for grades nine to ten compared with grades three to five. The reported adjusted odds ratio for paternal occupation in business, compared with farming, was 1.93 (95% CI: 1.10â3.39). The reported p-values and confidence intervals are not fully consistent; these estimates cannot establish independent associations without verification of the underlying model output (Table 5).
Table 5Association between the characteristics of the participants and the presence of HPV 16 antibodies
| Characteristics of the participants | Crude OR (95% CI) | Adjusted OR (95% CI) | Reported p-value |
|---|
| Age group (years) | | | |
| ââ9â13 | Ref | Ref | |
| ââ14â15 | 0.55 (0.36â0.84) | 0.61 (0.39â0.95) | 0.020 |
| Participantsâ educational qualification | | | |
| ââGrades 3â5 | Ref | Ref | |
| ââGrades 6â8 | 0.89 (0.61â1.29) | 0.88 (0.60â1.29) | 0.510 |
| ââGrades 9â10 | 0.51 (0.29â0.88) | 0.50 (0.28â0.89) | 0.004 |
| Mothersâ educational qualification | | | |
| ââNo schooling | Ref | Ref | |
| ââUp to primary | 1.73 (0.68â4.40) | 2.40 (0.66â8.68) | 0.182 |
| ââSSC | 2.59 (0.95â7.07) | 3.37 (0.82â13.76) | 0.090 |
| ââHSC | 3.64 (1.14â11.58) | 4.33 (0.91â20.73) | 0.057 |
| ââGraduate and above | 2.18 (0.69â6.95) | 3.73 (0.79â17.61) | 0.096 |
| Mothersâ occupation | | | |
| ââHousewife | Ref | Ref | |
| ââService holder | 1.05 (0.37â2.95) | 0.94 (0.33â2.67) | 0.903 |
| Fathersâ educational qualification | | | |
| ââNo schooling | Ref | Ref | |
| ââUp to primary | 0.99 (0.42â2.32) | 0.55 (0.17â1.72) | 0.302 |
| ââSSC | 1.46 (0.57â3.74) | 0.69 (0.20â2.42) | 0.556 |
| ââHSC | 2.68 (0.88â8.17) | 1.14 (0.28â4.67) | 0.854 |
| ââGraduate and above | 1.00 (0.38â2.61) | 0.44 (0.12â1.64) | 0.223 |
| Fathersâ occupation | | | |
| ââFarming | Ref | Ref | |
| ââGovernment job | 2.18 (1.09â4.34) | 1.99 (0.96â4.13) | 0.056 |
| ââPrivate job | 1.69 (0.94â3.05) | 1.57 (0.85â2.88) | 0.146 |
| ââBusiness | 2.06 (1.20â3.55) | 1.93 (1.10â3.39) | 0.023 |
| ââLiving abroad | 2.85 (1.15â7.05) | 2.26 (0.89â5.70) | 0.076 |
| ââDriver | 2.53 (0.65â9.88) | 2.85 (0.67â12.07) | 0.154 |
| Monthly income | | | |
| ââUp to Taka 10,000 | Ref | Ref | |
| ââTaka 10,001â20,000 | 0.80 (0.54â1.17) | 0.77 (0.52â1.15) | 0.201 |
| ââTaka 20,001â50,000 | 0.70 (0.41â1.19) | 0.65 (0.36â1.17) | 0.145 |
| ââTaka 50,001 and above | 0.99 (0.26â3.74) | 0.73 (0.19â2.91) | 0.654 |
Factors associated with HPV 18 antibody seropositivity
In the reported exploratory multivariable analysis for HPV18 seropositivity, participants from households earning BDT 10,001â20,000 and BDT 20,001â50,000 had adjusted odds ratios of 0.41 (95% CI: 0.26â0.67) and 0.21 (95% CI: 0.11â0.40), respectively, compared with households earning up to BDT 10,000. These estimates remain unverified and do not establish an effect of household income on immune response (Table 6).
Table 6Association between the characteristics of the participants and HPV 18 antibodies
| Characteristics of the participants | Crude OR (95% CI) | Adjusted OR (95% CI) | Reported p-value |
|---|
| Age group (years) | | | |
| ââ9â13 | Ref | Ref | |
| ââ14â15 | 0.87 (0.51â1.45) | 1.07 (0.62â1.85) | 0.801 |
| Participantsâ educational qualification | | | |
| ââGrades 3â5 | Ref | Ref | |
| ââGrades 6â8 | 0.92 (0.59â1.42) | 0.94 (0.60â1.48) | 0.782 |
| ââGrades 9â10 | 0.75 (0.38â1.45) | 0.74 (0.37â1.50) | 0.402 |
| Mothersâ educational qualification | | | |
| ââNo schooling | Ref | Ref | |
| ââUp to primary | 1.16 (0.37â3.59) | 0.71 (0.14â3.45) | 0.661 |
| ââSSC | 1.10 (0.33â3.61) | 0.59 (0.10â3.38) | 0.550 |
| ââHSC | 3.33 (0.74â14.95) | 1.75 (0.24â12.73) | 0.584 |
| ââGraduate and above | 1.86 (0.43â7.93) | 1.26 (0.17â9.34) | 0.821 |
| Mothersâ occupation | | | |
| ââHousewife | Ref | Ref | |
| ââService holder | 0.79 (0.25â2.44) | 0.77 (0.25â2.38) | 0.649 |
| Fathersâ educational qualification | | | |
| ââNo schooling | Ref | Ref | |
| ââUp to primary | 1.45 (0.59â3.56) | 1.17 (0.35â3.90) | 0.801 |
| ââSSC | 1.52 (0.56â4.09) | 1.46 (0.39â5.54) | 0.573 |
| ââHSC | 4.82 (1.27â18.21) | 4.02 (0.67â24.28) | 0.124 |
| ââGraduate and above | 2.52 (0.83â7.65) | 2.16 (0.51â9.09) | 0.293 |
| Fathersâ occupation | | | |
| ââFarming | Ref | Ref | |
| ââGovernment job | 1.43 (0.64â3.19) | 1.29 (0.52â3.19) | 0.589 |
| ââPrivate job | 1.28 (0.64â2.57) | 1.23 (0.59â2.56) | 0.576 |
| ââBusiness | 1.44 (0.76â2.74) | 1.39 (0.71â2.74) | 0.339 |
| ââLiving abroad | 2.09 (0.70â6.22) | 1.75 (0.57â5.34) | 0.329 |
| ââDriver | 1.06 (0.26â4.29) | 1.05 (0.23â4.81) | 0.951 |
| Monthly income | | | |
| ââUp to Taka 10,000 | Ref | Ref | |
| ââTaka 10,001â20,000 | 0.43 (0.27â0.70) | 0.41 (0.26â0.67) | <0.001 |
| ââTaka 20,001â50,000 | 0.26 (0.15â0.48) | 0.21 (0.11â0.40) | <0.001 |
| ââTaka 50,001 and above | 0.63 (0.13â2.98) | 0.29 (0.06â1.39) | 0.123 |
Discussion
The study reported HPV16/18 L1 IgG seropositivity after a single dose of bivalent HPV vaccination among girls in Bangladesh. The majority were classified in the reported nine-to-thirteen-year age category, whose reference time point is unclear. At follow-up, 72.8% of participants were reported as seropositive for HPV16 L1 IgG and 82.4% for HPV18 L1 IgG. These reported cross-sectional serological findings do not establish seroconversion, sustained immunity, or clinical protection, and their validity is limited by incomplete assay documentation. Serological monitoring may provide supplementary information on antibody seroprevalence after HPV vaccination. Serum collection provides information on antibody status, but it does not replace HPV DNA testing for infection. Kramer et al. also mentioned population-based sero-epidemiological studies to regularly monitor the impact of mass vaccination against HPV.22
Several trials have already reported high efficacy of a single-dose HPV vaccine against persistent HPV16/18 infection, among which the Costa Rica Vaccine Trial (CVT) and PATRICIA trials are notable.12,19 Data from the Finnish cohorts of the PATRICIA and FUTURE II randomized phase 3 trials showed persistence of detectable vaccine-induced antibodies after the bivalent or quadrivalent HPV vaccination for up to 12 years.23 In the CVT, although the antibody levels against HPV16 and HPV18 remained lower than those produced by three and two doses, the levels persisted for seven years, indicating long-lasting antibody persistence.24 Another study showed that over 90% of women remained HPV16 and 18 seropositive at both four and eleven years, with only 2.5% seronegative after one dose of the bivalent HPV vaccine.12 The present study reported lower seropositivity (72.8% for HPV 16 and 82.4% for HPV 18) than the CVT and other studies. Direct comparisons are limited by differences in study populations, baseline HPV status, assays, and seropositivity thresholds. In the present study, there was no opportunity to estimate pre-vaccination seropositivity status or presence of HPV 16/18 DNA in their cervix, nor was it possible to exclude participants who were sexually active. These limitations preclude attributing the between-study differences to vaccination response or prior HPV exposure. The persistence of vaccine-associated antibody responses is important, although seropositivity alone cannot establish clinical protection. In the present cross-sectional study, reported HPV18 L1 IgG seroprevalence (534/648, 82.4%) was higher than HPV16 L1 IgG seroprevalence (472/648, 72.8%) at follow-up. Without pre-vaccination serology, longitudinal antibody measurements, an unvaccinated control group, or clinical infection endpoints, these findings cannot establish seroconversion, antibody persistence, or protection against infection. Separately, long-term follow-up from the CVT found that over 98% of single-dose recipients remained seropositive for HPV16/18 up to 16 years post-vaccination, with only minor declines in antibody levels.25 A 2025 systematic review by Jeong and Jang analyzing randomized controlled trials reported that while single-dose recipients generally exhibit lower antibody titers than those receiving three doses, protective efficacy against HPV infection remained substantial, ranging from 53.9% to 100.0%.26 The reported age-related regression patterns remain exploratory because the age reference time point and the model output are not fully verified. These findings concern antibody seropositivity and do not measure the risk of acquiring HPV infection.
The reported multivariable models show different patterns across participant education, parental characteristics, and income categories. The unverified multivariable estimates prevent firm conclusions about sociodemographic correlates; these results do not show effects on HPV infection or vaccine response.
A study among Tanzanian girls aged nine to fourteen years showed that a single dose of the bivalent HPV vaccine induced a strong immune response up to 24 months and suggested this age group for vaccination.9 The antibody results reported in this study provide descriptive serological information from Bangladeshi girls after single-dose vaccination. Longitudinal studies with repeated antibody measurements, baseline data, and clinical infection endpoints are needed to evaluate antibody persistence and protection.
Though HPV vaccines were initially approved as three-dose regimens, later on, to reduce costs, a two-dose schedule was introduced for adolescents (nine to fourteen years old).27 Despite this, among a global cohort of 61 million 15-year-old girls in 2018, global HPV vaccination coverage remained very low (12.2%).28 Moreover, the COVID-19 pandemic had a negative impact on HPV vaccine rollout in LLMICs, causing disruptions in routine immunization, delays in introducing of new vaccines, and threatening HPV vaccine uptake.29 Nearly half of LLMICs failed to introduce HPV vaccination due to low affordability and the health emergency caused by the COVID-19 pandemic.30 Therefore, global elimination of CC may be better achieved using a single-dose regimen with higher coverage of the target population in LLMICs. Another study suggested similar benefits of a one-dose versus a two-dose regimen, including simplified delivery, reduced costs, and fewer vaccine supply constraints.31
The prevalence of high-risk HPV infections in Bangladesh is about 4.2%.32 To reduce the burden of CC and high-risk-HPV, the Government of Bangladesh (GOB) introduced a two-year pilot HPV vaccination program in Gazipur district in 2016 with support from the Global Alliance for Vaccines and Immunizations.33 The GOB decided to scale up a school-based vaccination program through EPI in collaboration with Global Alliance for Vaccines and Immunizations and development partners.34 Still, after completing the HPV vaccination demonstration program, Bangladesh had been awaiting the rollout of HPV vaccination since 2018. The long delay in scaling up vaccination may be related to vaccine manufacturing shortages, costs, and supply-related problems. Eventually, the GOB introduced a single-dose bivalent HPV vaccine into the national program on 2 October 2023, with a rollout plan to cover all eight divisions for girls aged 10 to 14 years.35 Recent advances in HPV vaccine development reinforce the viability of single-dose regimens as practical strategies for CC prevention in low- and middle-income countries. A preclinical study from Tianjin, China, demonstrated that a single-injection bivalent HPV vaccine using HPV16/18 VLPs delivered via an erodible tannic acid/polyethylene glycol film elicited robust humoral and cellular immune responses comparable to multi-dose regimens.36 Another 2025 study using sustained-release poly lactic-co-glycolic acid microparticles loaded with HPV VLPs showed prolonged antigen retention and potent immunogenicity in animal models.37
Global policy shifts further support single-dose strategies. In October 2024, WHO confirmed that the prequalified HPV vaccine Cecolin could be used in a single-dose schedule, endorsing the 2022 recommendation to transition from two-dose to more flexible single-dose schedules to alleviate global supply constraints.38 Additionally, real-world data from Thailand demonstrated 90.6% effectiveness of a single-dose bivalent HPV vaccine four years post-vaccination, comparable to 95.4% effectiveness of the two-dose regimen.39
External evidence supports consideration of single-dose schedules in resource-constrained settings such as Bangladesh. The reported HPV16 (72.8%) and HPV18 (82.4%) seroprevalence in this study does not by itself establish antibody durability or vaccine effectiveness, particularly given the unresolved assay and data-reporting limitations.
To maximize impact, expansion of single-dose HPV vaccination in Bangladesh should be guided by external effectiveness evidence and national immunization policy. This strategy can address challenges related to supply, logistics, and cost, ultimately enhancing vaccine uptake.
The unclear reference time point for age and the unverified regression results preclude age-specific recommendations based on this study. Future longitudinal research incorporating baseline serology, HPV DNA testing, and clinical outcomes in a broader female population could better inform population-level vaccine impact.
Limitations
Being limited to Dhaka, the findings may not fully represent rural or underserved populations. The school-linked recruitment may also limit representation of out-of-school girls. The cross-sectional design limits causal inference, and the absence of a control group makes it difficult to attribute antibody presence solely to vaccination. In addition, 322 of the 970 vaccinated girls (33.2%) were not included in the follow-up analysis, and purposive selection of sites may have introduced non-response and selection bias, limiting generalizability. Because pre-vaccination serology, baseline HPV DNA testing, an unvaccinated control group, and clinical infection endpoints were unavailable, the study cannot establish seroconversion or vaccine-derived clinical protection. The exact interval between vaccination and blood collection, and the reference time point for reported ages, are not consistently documented. Incomplete reporting of sample dilution and ELISA positivity calculations limits verification of the primary seroprevalence estimates. Unreconciled site-level follow-up counts and the unverified multivariable estimates further limit interpretation of the findings.
Despite these limitations, the study reports serological observations from a relatively large group of vaccinated girls in a low-resource setting. Its findings can inform the design of future studies, while conclusions about vaccination policy depend on stronger external evidence.
Conclusions
This study provides descriptive data on HPV16/18 L1 IgG seropositivity following single-dose bivalent HPV vaccination among girls in Dhaka, Bangladesh. The findings should be interpreted cautiously given the limitations in assay documentation and the exploratory nature of the sociodemographic analyses. Antibody persistence and clinical protection cannot be inferred from these data.
Declarations
Acknowledgement
The authors express sincere gratitude to BMU for their crucial financial and operational support, ensuring the success of this study. The authors are thankful to the colleagues of the relevant departments of BMU. The authors also thank the health managers, healthcare providers, school teachers in the study areas, the participating young girls and their families, the research team, and the data management team for their significant roles in this project.
Ethical statement
Ethical clearance was received from the Institutional Review Board of the BMU Ethics and Scientific Review Committee (Ref: No. BSMMU/2020/686, dated 16/01/2020). This study was conducted in accordance with the Declaration of Helsinki. Written informed consent was obtained from parents/guardians, and assent was obtained from participants.
Data sharing statement
Most of the data are contained within this published article. To preserve data privacy, the data used are not freely available. The authors confirm that the data will be shared upon a justified request.
Funding
The research received funding from BMU with memo No. BSMMU/2022/825. The funding covered the research activities, including transport costs, participant recruitment, blood sample collection, and essential laboratory expenses, ensuring the successful implementation of the study.
Conflict of interest
The authors declare no competing interests.
Authors’ contributions
Conception and design (AN, SAB, JF, FH), data collection and coordination of the field activities (NF, SJS, MFI, FH), arranged and supervised laboratory work (AN, SUM, JF), acquisition, analysis, and interpretation of data (AN, MFI, SUM, SJS), manuscript drafting and revising it critically (AN, MFI, SAB, NF, JF, SUM, SJS, FH), and approval of the final version of the manuscript (AN, MFI, SAB, NF, JF, SUM, SJS, FH).