Cross-immunity and age patterns of influenza A(H5N1) infection

Abstract

The age distribution of influenza A(H5N1) cases reported during 2006-2013 varied substantially between countries. As well as underlying demographic profiles, it is possible that cross-immunity contributed to the age distribution of reported cases: seasonal influenza A(H1N1) and avian influenza A(H5N1) share the same neuraminidase subtype, N1. Using a mechanistic model, we measured the extent to which population age distribution and heterosubtypic cross-immunity could explain the observed age patterns in Cambodia, China, Egypt, Indonesia and Vietnam. Our results support experimental evidence that prior infection with H1N1 confers partial cross-immunity to H5N1, and suggest that more than 50% of spillover events did not lead to reported cases of infection as a result. We also identified age groups that have additional risk factors for influenza A(H5N1) not captured by demography or infection history.

Keywords: mathematical modelling.

Fig. 1.

Demographic patterns of influenza A(H5N1) infection. Points show reported cases per million people, stratified by age group.

Fig. 2.

Comparison of reported cases in each country and model fits. (a–e) Results from model with cross-immunity only; (f–j) model with cross-immunity and age-dependent exposure risk. Dots show confirmed H5N1 cases in each 5-year age band; solid blue line shows model estimate; dashed lines give 95% credible intervals.