The Unseasonal Cold and Flu (Season)

Common cold coronaviruses are supposed to be seasonal (showing up in the drier, colder winter months), but the 2020-21 winter cold & flu season was almost nonexistent. It’s start got pushed out 3-4 months and peaked by the start of the summer. This is not normal. The impact from COVID-19 (not just infections, but lockdowns, mask wearing, social distancing, enhanced hygiene and reduced travel) had a huge impact on normally occurring respiratory diseases.

On January 12, 2021, the Fitzpatrick team published “The Missing Seasonal Flu and Common Cold Coronaviruses” to point out that seasonal flu and normally active common cold coronaviruses had become practically absent. In a normal common cold coronavirus season, these viruses slowly start in November, peak in January-March and drop sharply in April-May. During 2020, the common cold coronaviruses ended as expected (by the beginning of May), but failed to show up until mid-February, 2021 (a very late start).

Take a look at the graph above, for the Northeast USA from Nov. 10, 2021, and compare it to the January 12, 2021 graph below. We have just witnessed an unusual pattern for common cold coronaviruses in the USA (we are assuming it was unusual for the rest of the world as well). The “seasonal cold” just became unseasonal. Note there are three other USA geographic census regions which had similar start & peak dates – although they each had higher percent positive rates than the NE.

Image from January 10, 2021

Seasonal Flu:
Likewise, the Fitzpatrick team is interested in seeing if the “seasonal flu” pattern had gone cattywampus. In our January 12, 2021 post, we pointed out that the 2019-2020 seasonal flu cases had come to a strange and unusual stop just at the time when flu cases would normally start skyrocketing. Here is what we reported:

As COVID-19 was starting (New Years, 2020), seasonal flu was at a 10-year low. Now, this is what has happened in this past last year (up to now, November, 2021):

Normally, seasonal flu rates drop sharply by May. During 2021, seasonal flu rates inexplicitly started rising in July.

RSV: In 2021, the respiratory syncytial virus (RSV) that normally peaks in the winter, started rising in April – something doctors do not normally see. In June, 2021 the CDC issued an Emergency Preparedness Response alerting clinicians about increased inter-seasonal RSV. Experts warn that there is a build-up of susceptible, uninfected children who will be on the receiving end of a large infection wave in the future.

Rhinoviruses: Likewise, there was an unusually huge spike in the “number of positive tests” for rhinoviruses this past June-October 2021. Literally, peaking 10x higher than in normal years.

What happened to the “seasonality” of the seasonal flu and common cold coronaviruses? Did the spread of COVID-19 (the newest common cold coronavirus) impact the seasonal nature of all of the other common cold coronaviruses (NL63, OC43, HKU1, 229E), as well as influenza-like illnesses (ILI)?

In an excellent article published by AARP, Dr. Paul O’Rourke, an internist at Johns Hopkins, offered the following explanations to why these normally seasonal viruses are peaking mid-summer (instead of winter):

  • It’s a consequence of things returning to normal. “Normal” means getting a few colds in a year, but many people went a year WITHOUT having a cold.
  • People’s immune systems are NOT AS ROBUST because we’ve gone a year without our usual exposure to common bacteria and viruses.
  • Many children born in the last 2 years have very little exposure to microbes, which may explain why RSV cases rose in the summer.

Summary: While COVID-19 social distancing, closures and masking slowed disease spread, these measures pushed normally seasonal respiratory diseases out to spring/summer. We predict another somewhat later start to the 2022 common cold coronavirus & seasonal flu seasons.

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