At a glance
During the 2020-2021 season, the number of people hospitalized with flu was too low to generate stable burden estimates as is done for a typical flu season.
About the 2020-2021 flu season
Each year, CDC usually generates estimates of the number of illnesses, medical visits, hospitalizations and deaths that happen during a flu season—these estimates are used to collectively describe the annual burden of flu. To produce these estimates, CDC uses a mathematical model that is based in part on the number of people that are hospitalized with flu in our hospitalization surveillance network, FluSurv-NET.
Flu activity during 2020-2021 was the lowest it has been since current reporting began in 1997. Flu illnesses, hospitalizations and deaths were very low, probably well below the estimates for the 2011-2012 season, which was the mildest flu season in the decade between 2010 and 2020. Several measures that can be evaluated to understand how low flu activity was during the 2020-2021 season are described below.
Comparing flu activity with past seasons
One measure to help understand how low flu activity was during 2020-2021 is the cumulative number (or percent of specimens testing positive) of clinical lab-confirmed flu infections from the start of the typical flu season (week 40) through week 34, which is typically around the middle of August, from the past two flu seasons.
Season (up to Week 34)
Specimens tested by clinical labs
Total Positive Specimens
2020-21
1,480,295
2,265 (0.15%)
2019-20
1,491,430
250,396 (16.8%)
Comparing cumulative flu hospitalization rates with past seasons
Another measure is the FluSurv-NET cumulative hospitalization rates from 2020-2021 and 2019-2020.
- The overall cumulative hospitalization rate for the 2020-2021 flu season was 0.8 per 100,000 people.
- For the 2019-2020 flu season, the overall cumulative end-of-season hospitalization rate was 66.2 per 100,000 people.
- Putting this into context, in 2020-2021 only 8 out of every 100,000 people were hospitalized with flu.
It's important to note that FluSurv-NET covers approximately 9% of the U.S. population and rates may not necessarily be representative of the entire country.
Comparing flu hospitalizations reported with past seasons
Finally, we can look at the total number of hospitalizations reported through FluSurv-NET.
- During 2020-2021, 230 lab-confirmed hospitalizations were reported through FluSurv-NET.
- During 2019-2020, 19,302 lab-confirmed hospitalization were reported through FluSurv-NET.
It's important to note that this is not a comprehensive count of all flu hospitalizations in the United States. This is just a small subset reported to CDC for surveillance purposes. FluSurv-NET covers approximately 9% of the U.S. population and rates may not necessarily be representative of the entire country.