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Open AccessArticle

Serological Immunity to Smallpox in New South Wales, Australia

1
Biosecurity Program, Kirby Institute, Faculty of Medicine, University of New South Wales, Sydney, NSW 2052, Australia
2
Central Clinical School, University of Sydney, Sydney, NSW 2052, Australia
3
School of Medical Sciences, University of New South Wales, Sydney, NSW 2052, Australia
4
Surveillance Evaluation and Research Program, Kirby Institute, Faculty of Medicine, University of New South Wales, Sydney, NSW 2052, Australia
*
Author to whom correspondence should be addressed.
Viruses 2020, 12(5), 554; https://doi.org/10.3390/v12050554
Received: 21 April 2020 / Revised: 9 May 2020 / Accepted: 12 May 2020 / Published: 18 May 2020
(This article belongs to the Section Animal Viruses)
The re-emergence of smallpox is an increasing and legitimate concern due to advances in synthetic biology. Vaccination programs against smallpox using the vaccinia virus vaccine ceased with the eradication of smallpox and, unlike many other countries, Australia did not use mass vaccinations. However, vaccinated migrants contribute to population immunity. Testing for vaccinia antibodies is not routinely performed in Australia, and few opportunities exist to estimate the level of residual population immunity against smallpox. Serological data on population immunity in Australia could inform management plans against a smallpox outbreak. Vaccinia antibodies were measured in 2003 in regular plasmapheresis donors at the Australian Red Cross Blood Service from New South Wales (NSW). The data were analysed to estimate the proportion of Australians in NSW with detectable serological immunity to vaccinia. The primary object of this study was to measure neutralising antibody titres against vaccinia virus. Titre levels in donor samples were determined by plaque reduction assay. To estimate current levels of immunity to smallpox infection, the decline in geometric mean titres (GMT) over time was projected using two values for the antibody levels estimated on the basis of different times since vaccination. The results of this study suggest that there is minimal residual immunity to the vaccinia virus in the Australian population. Although humoral immunity is protective against orthopoxvirus infections, cell-mediated immunity and immunological memory likely also play roles, which are not quantified by antibody levels. These data provide an immunological snapshot of the NSW population, which could inform emergency preparedness planning and outbreak control, especially concerning the stockpiling of vaccinia vaccine. View Full-Text
Keywords: smallpox; vaccine immunity; response planning; population immunity smallpox; vaccine immunity; response planning; population immunity
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Costantino, V.; Trent, M.J.; Sullivan, J.S.; Kunasekaran, M.P.; Gray, R.; MacIntyre, R. Serological Immunity to Smallpox in New South Wales, Australia. Viruses 2020, 12, 554.

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