June 30, 2017
2 min read

Smallpox, BCG vaccines associated with decreased HIV-1 risk

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Smallpox and Bacillus Calmette-Guérin vaccination were both associated with a decreased risk for sexually transmitted HIV-1, according to researchers. The effect was stronger in women than in men, they said.

Studying the vaccines’ protective mechanisms could lead to a breakthrough HIV-1 vaccine, they wrote in Open Forum Infectious Diseases.

“So far, these results suggest that the mechanisms linking [Bacillus Calmette-Guérin (BCG)] and smallpox vaccines with protection against HIV-1 warrant further investigation,” the researchers wrote. “Hopefully, immunologists will investigate additional mechanisms for how smallpox and BCG vaccinations could possibly prevent HIV-1 and why such an effect might be stronger for women than men.”

The researchers cited previous studies suggesting that live vaccines may protect against nontargeted pathogens. Among them was one showing that the vaccinia virus used in the smallpox vaccine has features homologous to the HIV-1 envelope glycoprotein.

That, they said, suggests cross-reactive immunity is possible.

Other studies have shown that certain viruses inhibit HIV-1 replication and can increase the lifespan of those infected with HIV-1.

To investigate the potential effects of smallpox and BCG vaccination on HIV-1, the researchers assessed data from a cohort in Guinea-Bissau and one in Denmark.

The data from Guinea-Bissau were culled from an HIV prevalence survey conducted from May 2004 to December 2006 and a vaccination scar survey conducted between January 2005 and May 2007. In all, 1,751 participants were included in the cohort, 75 of whom (4.3%) had HIV-1.

In the vaccine scar survey, participants were assessed for the presence of no vaccination scars, smallpox vaccination scars only, BCG scars only or scars from both vaccinations. The numbers of scars for each vaccination type were also counted.

Participants with either or both scar types were less likely to have HIV-1, the researchers said (adjusted OR = 0.62; 95% CI, 0.36-1.07). Those with several smallpox vaccination scars were also less likely to have HIV-1 (aOR = 0.27; 95% CI, 0.10-0.75) than those with no scars.

Women with several smallpox vaccination scars were less likely to have HIV-1 than men with the same scars (aOR = 0.18; 95% CI, 0.05-0.64 and aOR = 0.52; 95% CI, 0.12-2.33, respectively; sex-differentiated effect, P =.29).

Among the 46,239 participants from Denmark, 104 HIV-1 cases were analyzed, along with a sub-cohort of 5,506 participants.

Their data were assessed on whether they had received one, both or neither vaccine. Participants who had one or both vaccines were less likely to have HIV-1 than those who had neither (aOR = 0.70; 95% CI, 0.43-1.15).


A meta-estimate combining the results of the Guinea-Bissauan and Danish cohorts was similar (aOR = 0.66; 95% CI, 0.46-0.96). Again, women had less of a risk for HIV-1 (aOR = 0.52; 95% CI, 0.32-0.84 and aOR = 0.77; 95% CI, 0.48-1.24, respectively, sex-differential effect, P = .26).

“The findings, if confirmed, could have major implications for future interventions against HIV-1,” they wrote. “Thus, future prospective studies are urgently warranted.” – by Joe Green

Disclosure: The researchers report no relevant financial disclosures.