Transmission potential of smallpox in contemporary populations

Despite eradication 1 , smallpox still presents a risk to public health whilst laboratory stocks of virus remain 2 , 3 . One factor crucial to any assessment of this risk is R 0 , the average number of secondary cases infected by each primary case. However, recently applied estimates have varied too...

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Veröffentlicht in:Nature (London) 2001-12, Vol.414 (6865), p.748-751
Hauptverfasser: Gani, Raymond, Leach, Steve
Format: Artikel
Sprache:eng
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Zusammenfassung:Despite eradication 1 , smallpox still presents a risk to public health whilst laboratory stocks of virus remain 2 , 3 . One factor crucial to any assessment of this risk is R 0 , the average number of secondary cases infected by each primary case. However, recently applied estimates have varied too widely ( R 0 from 1.5 to >20) to be of practical use, and often appear to disregard contingent factors such as socio-economic conditions and herd immunity 4 , 5 , 6 , 7 , 8 . Here we use epidemic modelling 9 to show a more consistent derivation of R 0 . In isolated pre-twentieth century populations 10 , 11 , 12 with negligible herd immunity, the numbers of cases initially rose exponentially, with an R 0 between 3.5 and 6. Before outbreak controls were applied, smallpox also demonstrated similar levels of transmission in 30 sporadic outbreaks in twentieth century Europe 1 , taking into account pre-existing vaccination levels 13 , 14 (about 50%) and the role of hospitals in doubling early transmission. Should smallpox recur, such estimates of transmission potential ( R 0 from 3.5 to 6) predict a reasonably rapid epidemic rise before the implementation of public health interventions, because little residual herd immunity exists now that vaccination has ceased.
ISSN:0028-0836
1476-4687
DOI:10.1038/414748a