12/12/2020
I’m getting lots of questions from patients and friends about why we are seeing so little influenza this year. Some have suggested that flu illnesses may be miscategorized as COVID and artificially inflating the numbers. Here’s the info I’ve shared with them.
Q: “Aren’t some of those COVID cases probably just influenza?
A:
1) No. COVID case numbers are determined by confirmed positive COVID test results. And while testing is not 100% sensitive and specific, especially the rapid tests (just like every other medical test we have) statistically we presume a certain small percentage of false positives and false negatives which mostly even out (https://www.cdc.gov/coronavirus/2019-ncov/lab/resources/antigen-tests-guidelines.html).
2) There is a strong possibility that some of the COVID+ individuals are also co-infected with influenza so we may be missing some of those +flu cases on our numbers, but we aren’t counting flu cases as COVID unless they ALSO tested + for COVID (https://www.cdc.gov/flu/professionals/diagnosis/testing-guidance-for-clinicians-hospitaized.htm)
Q: “Why are flu numbers so low this season?”
A:
1) We haven’t hit the flu surge in the northern hemisphere yet, which usually hits the last week or 2 of December (https://www.cdc.gov/flu/weekly/index.htm). Hopefully our trend of low rates continues since our hospital systems cannot handle even a MILD flu surge on top of the current COVID numbers.
2) We thankfully had record uptake in flu vaccination in the US this season, and are set to break last years’ previous record high (which was 4 million doses over the previous record year) by an additional 20 million doses. (https://www.cdc.gov/flu/season/faq-flu-season-2020-2021.htm). Widespread flu vaccination dramatically decreases transmission rates and disease severity.
3) As above, we may be missing some of our flu cases because they were co-infected with COVID-19 AND influenza at the same time. These numbers should be pretty low since many labs are performing combo COVID and flu testing on samples coming in as of the start of flu season (https://www.cdc.gov/flu/professionals/diagnosis/testing-guidance-for-clinicians-hospitaized.htm).
4) Many Americans are still limiting travel, keeping up with handwashing, wearing masks, and avoiding large gatherings. We know this also dramatically cuts down on flu transmission (https://www.cdc.gov/mmwr/volumes/69/wr/mm6937a6.htm)
Q:“So if masks are so great for influenza, why aren’t they cutting down on COVID cases?”
A: THEY ARE! Unfortunately COVID-19 is significantly more contagious than influenza, meaning that without aggressive mitigation strategies, one contagious COVID case will likely infect many more people than one contagious flu case. Also COVID infected individuals are contagious for a longer period of time, most notably BEFORE they develop symptoms (https://www.cdc.gov/flu/symptoms/flu-vs-covid19.htm). So while masks, distancing, and hand hygiene help A LOT, we really need EVERYONE to be doing their part and that just has not happened in the US.
https://www.cdc.gov/flu/weekly/index.htm