Question: I haven’t heard much about flu season recently.  I remember that it was mild in the Southern Hemisphere.  Is that the case for the Northern Hemisphere?

Answer: We last talked about influenza in our Q&A of 10/21, finding that seasonal influenza rates were low.  Approximately 2.5 months later, influenza rates remain low.  In this week’s influenza report, CDC states that flu activity in the US is “lower than usual for this time of year.”  For week 52 (ending December 26th), 36,953 specimens were tested across the country, of which 76 (0.2%) were positive.  As you can see in Figure 1, only one state has moderate flu activity, Mississippi.  CDC also reports that “A total of 101 laboratory-confirmed influenza-associated hospitalizations occurring between October 1, 2020 and December 26, 2020 were reported by FluSurv-NET sites. This number is lower than average for this point in the season and comparable to counts seen at this point during the 2011-12 season.”  

A number of studies have been published around the world examining influenza activity during the pandemic.  Evidence continues to accumulate that non-pharmaceutical interventions (NPIs)– mask wearing, distancing, hand washing– are highly correlated with lower influenza rates (a few examples here, here, here, and here).  One could also hypothesize that testing for influenza has been limited due to the pandemic, but even in Australia where flu testing increased in 2020 compared with previous years, influenza was much lower than previous seasons.  One could also hypothesize that increased influenza vaccination has tamped down influenza rates.  CDC reports that 192.3 million doses of influenza vaccine were distributed across the country as of 12/25, which is 17.8 million doses more than the 2019-20 flu season.  However, a recent MMWR report found that “early-season data do not indicate substantial differences in intended influenza vaccination behavior during the 2020–21 influenza season compared with other recent seasons.”  One positive of all the behavior change because of the pandemic is that influenza and other respiratory infections have become far more rare.   

Figure 1. Influenza Map, December 26th (from CDC)