Administration of hepatitis B vaccine in winter as a significant predictor of the poor effectiveness of vaccination in rural Mongolia: evidence from a nationwide survey
- Dambadarjaa Davaalkham1,
- Toshiyuki Ojima1,
- Steven Wiersma2,
- Tserenkhuu Lkhagvasuren3,
- Pagvajav Nymadawa4,
- Ritei Uehara1,
- Makoto Watanabe1,
- Izumi Oki1,
- Yosikazu Nakamura1
- 1Department of Public Health, Jichi Medical University School of Medicine, Tochigi, Japan
- 2Department of Immunization, Vaccines and Biologicals, World Health Organization, Geneva, Switzerland
- 3Health Sciences University, Ulaanbaatar, Mongolia
- 4National Center for Communicable Diseases, Ulaanbaatar, Mongolia
- Correspondence to: Dr D Davaalkham Department of Public Health, Jichi Medical University School of Medicine, 3311-1 Yakushiji, Shimotsuke, Tochigi 329-0498, Japan; davaamon{at}jichi.ac.jp
- Accepted 13 October 2006
Abstract
Background: Universal hepatitis B (HB) immunisation is the most effective means for prevention of hepatitis B virus (HBV) infection worldwide. Maintaining the vaccine cold chain is an essential part of a successful immunisation programme. Our recent nationwide survey in Mongolia has observed significant urban–rural differences in the prevalence of HBV infection among vaccinated cohorts.
Objective: To examine whether the administration of HB vaccine in winter contributes to these residential discrepancies on the effectiveness of vaccination.
Design and setting: In 2004, a nationwide serosurvey was carried out covering both urban and rural areas of Mongolia. Sampling was multistage, with random probability from all public schools in the country.
Participants: A random sample of 1145 children (51.7% boys; aged 7–12 years), representative of Mongolian elementary school children.
Results: Multivariate logistic regression analysis identified that total (past and current) HBV infection (OR 2.31, 95% CI 1.20 to 4.42; p = 0.012) was independently associated with the administration of all HB vaccines in winter. An increased OR for current HBV infection was also observed (OR 2.58, 95% CI 0.87 to 7.68; p = 0.089), but without significance. Interestingly, after stratifying by residence, the association between winter vaccination and total HBV infection was evident for rural (p = 0.008) but not for urban areas (p = 0.294). The frequency of vaccine-induced immunity was significantly (p = 0.007) lower for those who received HB vaccine at birth during winter in rural areas.
Conclusion: Administration of HB vaccine during winter is an important predictor of the low effectiveness of vaccination in rural Mongolia. To improve the effectiveness of HB vaccination in remote areas, cold chain control should be addressed with particular attention to the winter season.
- anti-HBc, antibody against hepatitis B core antigen
- anti-HBs, antibody to hepatitis B surface antigen
- EPI, Expanded Program on Immunization
- HB, hepatitis B
- HbsAg, hepatitis B surface antigen
- HBV, hepatitis B virus
- WHO, World Health Organization
Footnotes
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Funding: This study was supported by grants from the World Health Organization, Switzerland (Number WP/MOG/IVD/216/XC/04991.00) and Jichi Medical University, Japan.
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Competing interests: None.
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This study was approved by the Ethical Review Committees of the World Health Organization, Switzerland; Ministry of Health, Mongolia; and Jichi Medical University, Japan.
