Volume 28, Number 5—May 2022
Research
Determining Existing Human Population Immunity as Part of Assessing Influenza Pandemic Risk
Jonathan Tin Lai Cheung, Tim K. Tsang, Hui-ling Yen, Ranawaka A.P.M. Perera, Chris Ka Pun Mok, Yong Ping Lin, Benjamin J. Cowling, and Malik Peiris
Table 4
Estimations of overall population-level immunity against historical H2 and H1 pandemic viruses and the potential effect of population immunity on reproduction number among persons in Hong Kong, China*
| Virus strain | Proportion of population immune (95% CI) | Relative reduction in R0 (95% CI) | Smallest R0 needed to cause pandemic (95% CI) |
|---|---|---|---|
| A/Singapore/1/1957 (H2N2) |
0.37 (0.346–0.394) |
0.321 (0.295–0.348) |
1.472 (1.419–1.535) |
| A/California/04/2009 (H1N1) | 0.117 (0.098–0.14) | 0.115 (0.096–0.138) | 1.13 (1.106–1.16) |
*Serum samples for testing antibodies to the 1957 virus were collected in 2011 and those for testing antibodies to the 2009 virus were collected in 2008–2009.
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