Phase-out of smallpox vaccination and the female/male HIV-1 prevalence ratio: an ecological study from Guinea-Bissau

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  • Andreas Rieckmann, Section of Epidemiology, Department of Public Health, The University of Copenhagen, Copenhagen, Denmark, Research Center for Vitamins and Vaccines (CVIVA), Bandim Health Project, Statens Serum Institut, Copenhagen, Denmark; OPEN, Odense Patient Data Explorative Network, Odense University Hospital/Department of Clinical Research, University of Southern Denmark, Odense, Denmark.
  • ,
  • Marie Villumsen, Center for Clinical Research and Prevention, Bispebjerg and Frederiksberg Hospital
  • ,
  • Bo Langhoff Hønge
  • Signe Sørup
  • Amabelia Rodrigues, Bandim Health Project, Indepth Network, Bissau, Guinea-Bissau; National Public Health Laboratory, Bissau, Guinea-Bissau.
  • ,
  • Zacarias Jose da Silva, National Institute of Public Health (INASA), Bissau, Guinea-Bissau.
  • ,
  • Hilton Whittle, London School of Hygiene and Tropical Medicine
  • ,
  • Christine Benn, Research Center for Vitamins and Vaccines (CVIVA), Bandim Health Project, Statens Serum Institut, Copenhagen, Denmark; OPEN, Odense Patient Data Explorative Network, Odense University Hospital/Department of Clinical Research, University of Southern Denmark, Odense, Denmark.
  • ,
  • Peter Aaby, Bandim Health Project, Indepth Network, Bissau, Guinea-Bissau; National Public Health Laboratory, Bissau, Guinea-Bissau.

OBJECTIVE: In Guinea-Bissau, West Africa, we observed that having a smallpox vaccination scar was associated with lower HIV-1 prevalence, more strongly for women than men. If this represents a causal effect, the female/male HIV-1 prevalence ratio would increase for birth cohorts no longer receiving smallpox vaccination due to the phase-out of this vaccine.

DESIGN: An ecological design using HIV surveys and information about smallpox vaccination coverage.

SETTING: Urban and rural Guinea-Bissau.

PARTICIPANTS: Participants in HIV surveys were grouped into an age group with decreasing smallpox vaccination coverage (15-34 years) and an age group with steady smallpox vaccination coverage (≥35 years).

INTERVENTIONS: The exposure of interest was the phase-out of the smallpox vaccine in Guinea-Bissau.

PRIMARY AND SECONDARY OUTCOME MEASURES: HIV-1 prevalence.

RESULTS: At both sites, the female/male HIV-1 prevalence ratio increased by calendar time for the age group with decreasing smallpox vaccination coverage; the combined female/male HIV-1 prevalence ratio among people aged 15-34 years was 1.00 (95% CI 0.17 to 5.99) in 1987-1990, 1.16 (95% CI 0.69 to 1.93) in 1996-1997, 2.32 (95% CI 1.51 to 3.56) in 2006-2007 (p value for no trend=0.04). There was no increase in the female-to-male HIV-1 prevalence ratio for the age group >35 years with steady smallpox vaccination coverage; 1.93 (95% CI 0.40 to 9.25) in 1987-1990, 1.32 (95% CI 0.83 to 2.10) in 1996-1997, 0.81 (95% CI 0.56 to 1.16) in 2006-2007 (p value for no trend=0.07).

CONCLUSIONS: Thus, data was compatible with the deduction that the phase-out of smallpox vaccination may have increased the susceptibility to HIV-1 relatively more for women than men. Hence, phasing out smallpox vaccination may have contributed to the global increase in the female/male HIV-1 prevalence ratio among young individuals. Due to the potential fallacies of ecological studies, the results should be interpreted carefully, and this hypothesis needs further assessment. If the hypothesis is true, studies of smallpox vaccination could inform HIV-1 vaccine research.

Original languageEnglish
Article numbere031415
JournalBMJ Open
Volume9
Issue10
Number of pages7
ISSN2044-6055
DOIs
Publication statusPublished - Oct 2019

    Research areas

  • HIV-1, Vaccinia, heterologous immunity, non-specific effects of vaccines, smallpox vaccination

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