The Missing Seasonal Flu and Common Cold Coronaviruses

The Missing Seasonal Flu:

Seasonal influenza attacks are significantly LESS than the previous 6 years (flu seasons). Why?

  • The CDC suggests that ILI (influenza-like illness) may be impacted by the COVID-19 pandemic. We interpret this as being reflective of social distancing, masking and less human interactions.

  • Authorities saw an “abrupt and early halt” to the 2019-20 Northern Hemisphere flu season, which may be attributed to strict lockdowns in the spring. Interestingly, this resulted in only 22,000 flu deaths (which is the lower end of the typical 12,000 – 61,000 range).

The USA 2020-21 flu season map for the week ending Dec. 26, 2020 shows next to no activity.

The 2020-2021 flu vaccine distribution is also the highest it has been in 5 years. 

We cannot find 2020-2021 flu vaccine efficacy data (likely because there are so few cases), so we looked to South America (who already had their flu season). They also reported very low flu virus detections - due to travel restrictions, COVID-19 mitigation strategies and social distancing.

The Missing Common Cold Coronaviruses:

  • The 4 common coronaviruses (ccc’s) tend to circulate every other or every third year, but they will all have some level of activity each year.  We described each of the coronaviruses in our September 2020 blog “The COVID-19 Immunity Blog”.

  • In each of the past two seasons (2018-19 and 2019-20), activity (new cases) started to increase by mid-November, with at least one strain peaking by mid-December.

The Fitzpatrick team has been watching the biweekly activity (or lack thereof) for the 4 common cold coronaviruses. We hypothesize that the widespread prevalence of COVID-19 is preventing any of these 4 viruses from gaining traction. The brightest minds in science are hinting likewise in this excellent article in NATURE from Dec. 15, 2020.

Based on CDC and European data, we would expect the C43 & NL63 common cold coronaviruses to appear this winter season (in the northern hemisphere) because they both peaked two years ago and have been on an approximately every-other year cycle:

  • All of the 4 common cold coronaviruses tend to circulate December – May, but can push out to June/July. Since they are running two months late this season (not even showing up yet), it will be interesting to see IF ANY show up, and more importantly, will they push aside COVID-19 going forward?

  • It seems that ccc 229E is a wild card. It is the most unpredictable of the 4 as to when it will present. As noted in our immunity blog, 229E has been known to cause severe disease, mostly affects immunocompromised patients (70% of 229E cases) and is the only ccc that we know of that causes anosmia. From this 2010 European study, we learned that 229E has the greatest prevalence in patients >65.

Additional Flu and Common Cold Coronavirus Facts Amid COVID-19:

  • Experts say the R0 (Reproductive Rate) for COVID-19 is higher than for the flu, so it is transmitted a lot easier.

  • We share the R0 for a variety of preventable diseases in our September 2020 vaccination post for influenza - it is between 1.0 and 2.0.  Whereas, COVID-19 R0 is around 2.87. We will provide an in-depth explanation of COVID-19 Reproductive Rate in an upcoming blog.

  • RSV cases (respiratory syncytial virus) in young children have dropped by 98% in parts of Australia, and have not arrived in mainland USA since April, 2020.

  • Rhinovirus infections dropped by more than half in the UK during the lockdown, but shot back up once schools opened – to higher than normal expected cases.


As we forecasted in our December 9, 2020 COVID-19 ENDGAME TIMELINE post, COVID-19 cases will dramatically fall in February, 2021 (as it is running out of potential hosts and we are approaching herd immunity). We may see an emergence of ccc’s at that point. In fact, we might also start seeing more seasonal flu and RSV cases.

Kevin Fitzpatrick, Fitzpatrick Translational Science

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