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.