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

Abstract

ObjectiveIn 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.DesignAn ecological design using HIV surveys and information about smallpox vaccination coverage.SettingUrban and rural Guinea-Bissau.ParticipantsParticipants 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).InterventionsThe exposure of interest was the phase-out of the smallpox vaccine in Guinea-Bissau.Primary and secondary outcome measuresHIV-1 prevalence.ResultsAt 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).ConclusionsThus, 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.

Relationship between Influenza Vaccination Coverage Rate and COVID-19 Outbreak: An Italian Ecological Study

“…Although our findings do not allow for assumptions to be made about the mechanisms underlying the putative protective role of influenza vaccination on COVID-19 outcomes, previous immunological and epidemiological studies [35][36][37][38][39], as well as mathematical models [40][41][42], support the concept that vaccination against one microorganism may affect the host's response to other infectious agents. For example, vaccination against mycobacterium tuberculosis with the bacillus Calmette-Guérin vaccine significantly increases the secretion of IL-1B (a pro-inflammatory cytokine), which plays a recognized role in antiviral immunity [43].…”

Possible Mpox Protection from Smallpox Vaccine–Generated Antibodies among Older Adults

“…Furthermore, endemic cases in high-income countries declined greatly during the 1950s (9). Taken together, those data illustrate that smallpox vaccination coverage steadily declined in most high-income Western countries as smallpox was increasingly confined to low-income countries (7). Although an imported outbreak in Yugoslavia in 1972 caused 175 cases and 35 deaths, the last nonimported case in Europe was declared in 1953 (10); after that date, persons became less likely to receive smallpox vaccination.…”

“…Although guidelines for recommended smallpox vaccination did not change during 1937–1980 in most countries in Europe, vaccination coverage in Spain and other countries declined continuously as disease eradication progressed ( 5 , 6 ). For example, a 2019 article reported that smallpox vaccination coverage in Guinea-Bissau fell dramatically during the 1970s, from 75% to 10%–25% ( 7 ). Another study, conducted in Denmark, reported that vaccination coverage dropped from 95% in 1965 to 5%–20% among persons born during the 1970s ( 8 ).…”