Levels of influenza and non-COVID-19 respiratory viruses were at historically low levels for most of 2020 new report from disease control and prevention centers. The flu is still circulating very little, but other viruses – including parainfluenza viruses and common human coronaviruses that cause colds – will have a recurrence out of season in 2021.
Between October 2020 and May 2021, influenza concentrations in the United States were the lowest since 1997, the first year of influenza season data, the analysis found. Very little was reported about the flu around the world, and experts believe that the protective measures people took against COVID-19 – camouflage, distance – suppressed the virus.
The near-non-existent flu season this year could mean that this fall and winter flu season could be more severe, the CDC report warned. Because there wasn’t a lot of flu around, people may not have been exposed to the virus at the same rate as usual. It can dull the normal level of viral immunity. “A lower level of immunity in the population, especially among younger children, could mean a broader disease and possibly a more serious epidemic when the influenza virus cycle returns,” the report’s authors wrote. This means it is particularly important for doctors and nurses to encourage people over the age of six months to get flu shots this fall, they said.
Respiratory syncytial virus (RSV), a virus that causes colds in adults but can be dangerous to infants, blood circulation was also muted in 2020 and early 2021. Prices began to rise in April 2021, which is unusual – normally, levels of the virus peaked in January. The trend for parainfluenza viruses and common human coronaviruses was similar: levels were low until 2020 and then began to rise in February 2021.
Public health measures used to slow the spread of COVID-19 were likely to help suppress these viruses during 2020, and they recovered as U.S. communities began to remove some of these restrictions. It is not yet clear how the flu and various cold-causing viruses will respond to anti-COVID-19 strategies, so trends in these viruses may be unpredictable over the next year as efforts to fight the pandemic continue.
“Physicians should be aware that respiratory viruses may not have typical seasonal circulatory patterns and that the circulation of certain respiratory viruses may begin again,” the CDC report said.
The proliferation of common rhinitis viruses may also make it more difficult to distinguish between people and their doctors between the symptoms of COVID-19 and the symptoms of other diseases. In 2020, all cold or flu-like symptoms were probably COVID-19 – it was one of the only viruses. Now that other viruses are on their way back, the image may be darker.