Pandemic influenza H1N1: reconciling serosurvey data with estimates of the reproduction number.

BACKGROUND

During the 2009 pandemic of influenza A (H1N1), many studies reported estimates of the reproduction number from outbreak data. Since then, seroprevalence studies have been conducted in a number of countries to assess the proportion of the population that was infected in the first wave of the pandemic.

METHODS

Here, we collate the reproduction number estimates, and use mathematical models to reconcile these with serosurvey data.

RESULTS

Most estimates of the reproduction number from outbreaks are in the range of 1.0-2.0, whereas mean estimates calculated from seroprevalence data range from 1.14 to 1.36. Age-specific analysis of these data suggests that the reproduction number for children was approximately 1.6, whereas the reproduction numbers for adults >25 years of age was less than 1.0.

CONCLUSION

The difference between age-groups may help to explain high estimates of the reproduction number from outbreaks involving a large proportion of child cases.