Humoral immunity, vaccination period and demographic characteristics of first immunized smallpox vaccine recipients

Abstract

Mass vaccination with vaccinia virus resulted in smallpox eradication, that was later cancelled due to potential of developing severe complications. Reappraisal of scientific interest to smallpox vaccine was accounted for by emerged threat of using relevant virus as a bioweapon as well as increased frequency of orthopoxvirus infections paralleled with decline in population immunity. The vaccinia virus is also used as a vector for generating recombinant vaccines. Understanding mechanisms behind formation of immune response and opportunity for forecasting its modality may allow to avoid potential adverse events and excessive immunization.The aim of the study was to assess a link between humoral immunity, clinical signs related to vaccination period, adult sex and age characteristics in subjects received several doses of vaccinia virus. We examined vaccination-coupled clinical data obtained from 135 subjects revaccinated with a smallpox vaccine for 2-10 times. It was found that 95% and 5% vaccine recipients experienced mild or moderate vaccination-related signs, respectively.Inoculation skin lesions were observed in 127 subjects (94.1%), whereas 22% vaccine recipients experienced local and systemic adverse events. Mild vs. moderate vaccine signs group manifested greater hyperemia (p=0.04), scabbing (p=0.01), and duration of healing time (p=0.001). Younger subjects (p=0.03) and more frequent axillary adenopathy (p<0.001) were observed in moderate vs. mild vaccination period were at lower rate (p = 0.03), lymphadenopathy developed more often during moderate vaccination period (p<0.001).Vaccinia virus-neutralizing antibody titers were measured in 54 subjects by using plaque reduction neutralization tests. It was noted that protective antibody level tended to rise in females vs. males. A negative correlation between antibody titers and hyperemia degree was observed. Frequent axillary adenopathy was associated with higher serum protective antibody level. Vaccinia-virus neutralizing antibody titers were not associated with presence and size of inoculation lesion, elimination of skin crusts, age and previous vaccination records. The clinical variability and immune response after applying this vaccine by similar vaccination protocol would be accounted for by individual genetic differences remains to be further explored.