The global eradication of smallpox in the 1980s was achieved by intradermal vaccination with vaccinia virus. A study published in PLOS pathogens by Evgeniya V. Shmeleva, Brian J. Ferguson and Geoffrey L. Smith at the University of Cambridge, UK and colleagues shows that there is a large increase in skin bacteria and suggests that this may improve the immune response.
The smallpox vaccination was administered via multiple skin punctures and this method of vaccination may have introduced local bacteria into the vaccination site. However, the effect of smallpox vaccination on skin microbiota and whether these bacteria affect vaccination efficacy is not well understood. To study the role of bacteria in the immune response to smallpox vaccination, the researchers used a mouse model with germ-free mice as well as normal mice, some of which were treated with antibiotics. The mice were vaccinated with the vaccinia virus, after which the researchers analyzed the immune responses of each group.
The researchers found a 1000-fold increase in skin microbiota, greater lesions, and higher antibody levels following intradermal vaccination of non-germ-free mice, suggesting an enhanced skin inflammatory response in the presence of bacteria. Animals that were germ-free or treated with antibiotics had smaller infection-related lesions and less skin inflammation. However, all groups had an equal number of memory T cells and similar protection against reinfection. The study was limited to vaccinating mice with vaccinia virus and further research is needed to determine if these results in mice can be extrapolated to other vaccines or to human vaccination.
According to the authors, “This study highlights the role of commensal bacteria in enhancing the immune response after skin vaccination and has implications for other vaccines based on infectious poxviruses or other viral vectors that are administered by skin vaccination.
The authors add: “We found that skin vaccination with the smallpox vaccine resulted in a large increase in local bacteria, which increased the size of the vaccine lesion and affected the immune response. This suggests that manipulation of commensal skin microbiota could be a way to improve the efficacy of intradermal vaccines.
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