Since October, all rapid SARS-CoV-2 PCR tests performed at the hospital laboratories where I work have included a PCR test for flu. But of the thousands of tests performed, not one positive flu has been detected. Has COVID cured flu?
No, I don’t believe that COVID has cured the flu, but I believe that masks have dramatically reduced the prevalence of flu in the community. Flu is a respiratory infection, passed from person to person by the same transmission mode as COVID, mainly inhaled droplets from an infected person. Standard face coverings reduce flu transmission in two ways. First, droplets from an infected person are less likely to be spread into the surrounding air; instead, they hit the mask and fall. Second, the mask helps filter the air of droplets that may contain viral particles. The result is a reduction, but not an elimination, of respiratory viral transmission.
So why haven’t masks cured COVID? SARS-CoV-2 is more infectious than flu, meaning that compared to flu, far fewer SARS-CoV-2 viral particles are needed to cause infection. Masks reduce the number of viral particles in the air, but they don’t eliminate them. Some virus leaks out from the masks of infected persons, and some virus can be inhaled by masked individuals nearby. It’s a matter of how much virus gets inhaled. It takes much more flu to cause infection than SARS-CoV-2. Masks slow the spread of COVID-19, but do not eliminate disease the way masks have flu.
We may use this COVID/Flu comparison to make some predictions about the B.1.1.7 variant, the “variant of concern” now reported in at least 70 countries. This variant is reported to be much more infectious than the standard SARS-CoV-2 virus, about fifty percent more, with the consequence that masks may not be enough to slow its spread through the community. Tighter, less permeable, and more uncomfortable masks may be necessary to protect against this variant as it spreads across our nation. The higher transmission rate also predicts that this variant will soon be the dominant form of the SARS-CoV-2 virus in the U.S.
If standard face coverings may soon become less effective protection against COVID-19, maybe now is the time to learn about different types of masks. We will do that next time.
2 replies on “Where’s the Flu?”
[…] What about the coming B.1.1.7 variant of SARS-CoV-2? I want to be very clear: the FDA does not recommend the general use of an N95 or higher rated mask for COVID-19 prevention. Although N95 masks protect against SARS-CoV-2, there continues to be supply shortages of these masks. Therefore, the FDA recommends that their use be reserved for health care providers. However, as we discussed last time, there may soon be a time that this recommendation changes. It is possible that an N95 mask will be required to protect against the B.1.1.7 variant because of its higher transmission rate. […]
[…] voluntary or mandated, changed the rhythm of upper respiratory infections like RSV and Flu. Flu has yet to return; the last infection diagnosed in my practice was in May, 2020, at the tail of the 2019-2020 […]