Influence of Population Immunosuppression and Past Vaccination on Smallpox Reemergence.

C Raina Macintyre,Valentina Costantino,Anthony Kelleher,Eva Segelov,John Michael Lane,Xin Chen,Abrar Ahmad Chughtai,Mohana Kunasekaran

doi:10.3201/eid2404.171233

Abstract

We built a SEIR (susceptible, exposed, infected, recovered) model of smallpox transmission for New York, New York, USA, and Sydney, New South Wales, Australia, that accounted for age-specific population immunosuppression and residual vaccine immunity and conducted sensitivity analyses to estimate the effect these parameters might have on smallpox reemergence. At least 19% of New York’s and 17% of Sydney’s population are immunosuppressed. The highest smallpox infection rates were in persons 0–19 years of age, but the highest death rates were in those >45 years of age. Because of the low level of residual vaccine immunity, immunosuppression was more influential than vaccination on death and infection rates in our model. Despite widespread smallpox vaccination until 1980 in New York, smallpox outbreak severity appeared worse in New York than in Sydney. Immunosuppression is highly prevalent and should be considered in future smallpox outbreak models because excluding this factor probably underestimates death and infection rates.

Highlights

We built a SEIR model of smallpox transmission for New York, New York, USA, and Sydney, New South Wales, Australia, that accounted for age-specific population immunosuppression and residual vaccine immunity and conducted sensitivity analyses to estimate the effect these parameters might have on smallpox reemergence
Population and Immunity Levels We examined the population age distributions of New York and Sydney
Sydney has a higher percentage of persons 55 years of age than New York (Figure 1, panel A), whereas New York has a higher proportion of persons 20–39 years of age than Sydney

Summary

Introduction

We built a SEIR (susceptible, exposed, infected, recovered) model of smallpox transmission for New York, New York, USA, and Sydney, New South Wales, Australia, that accounted for age-specific population immunosuppression and residual vaccine immunity and conducted sensitivity analyses to estimate the effect these parameters might have on smallpox reemergence. Because of the low level of residual vaccine immunity, immunosuppression was more influential than vaccination on death and infection rates in our model. Immunosuppression is highly prevalent and should be considered in future smallpox outbreak models because excluding this factor probably underestimates death and infection rates. The fact that the proportion of unvaccinated and immunosuppressed persons in the population is increasing has not yet been adequately considered in estimations of the effect of reemergent smallpox. 2 large cities with different vaccination histories for which estimates could be made on the population’s immunologic status

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Conclusion