The H1N1 Factor and Inverse Correlation Between Death Rates Due to COVID-19 and Influenza-Pneumonia

In an earlier study, we had observed an inverse correlation between death rates due to COVID-19 and influenza, suggesting cross-immunity. We examine virus surveillance data further to identify the key subtype of influenza virus that seems to give such cross-immunity. This is identified as the H1N1 strain and we show that a country where this strain was recently dominant has much lower COVID-19 mortality rates. It is possible to argue that many countries which already have a high burden of influenza and pneumonia- related deaths, may have a substantial fraction of the population immune to the SARS-CoV-2 virus and hence experience lower mortality rates at the peak typical of exponentially growing epidemics. This has implication on policies appropriate for managing the epidemic.