The COVID pandemic appears to be causing a flu-season double-whammy – increased risk and decreased attention. It starts with the fact that during the last two years the severity of flu seasons have been dramatically diminished:
The Centers for Disease Control and Prevention (CDC) recently reported that it had logged 1,316 positive flu cases in its surveillance network between September 2020 and the end of January 2021. During that same period last year, the CDC had recorded nearly 130,000 cases.
Flu cases partially rebounded last year, but were still historically low. Almost certainly the reason for this decrease in flu cases is because of the implementation of masking and social distancing – because these methods work to prevent the spread of respiratory infections. And now the flu, and other respiratory infections, are rebounding with a vengeance.
The reason for this is what experts call immunity debt. Our immune systems respond to challenge with a virus or other infectious agent by not only responding with an immediate immune response, but with long-term immunity. Among other mechanisms, for example, memory B-cells that produce antibodies with fine-tuned affinity for the infecting agent can have a robust immediate response on later exposure.
But immunity generally wanes over time (at varying rates depending on the type of organism and degree of initial immune reaction). Some vaccines, such as those for measles, rubella, and diphtheria, provide good life-long immunity. But the flu has particularly short-lived immunity from infection or vaccine, waning after only a few months. This is because some of the immune cells involved in that immunity are short-lived. Immunity is complex, however, and other aspects of immunity may last for years. In addition, there is evidence that repeated annual flu vaccines provide some cumulative benefit, reducing mortality from the flu especially in older adults. The flu strains also drift every season, evading prior immunity to some extent.
It is likely that exposure to the flu every year, even if one doesn’t develop a clinical infection, may provide a little boost to immunity. If, however, the general population has essentially gone two years with little or no exposure to flu viruses, we are missing this boost – and that’s the immunity debt. Plus, we also now have a crop of young children who have never been exposed to the flu.
For these reasons experts are expecting a worse than normal flu season. In fact, early cases are already worse than average. In fact, some are warning of a “tripledemic” with a spike in COVID cases, a bad flu season, and a bad season for RSV and other respiratory viruses.
The best thing you can do to protect yourself and others is to get vaccinated. If you have not yet had your annual flu vaccine, get it as soon as possible. The flu season is already underway – but it’s not too late, as the season is likely to last for months. Get fully boosted against COVID, and get your flu vaccine. You can get them at the same time, but spreading them out over a few days to limit side effects is reasonable.
This brings us to the second part of the double whammy – despite the fact that we are facing a worse than average flu season, vaccine uptake is down. According to the CDC we are at about 5 million fewer doses given than at the same time last year. It’s always hard to know exactly why aggregate behavior shifts. There are lots of factors to consider, so we don’t really know why fewer flu vaccines are being given this year.
It is possible, however, that we are partly seeing the effect of pandemic fatigue. People are simultaneously tired of having their life disrupted by the COVID-19 pandemic, and yet COVID still is occupying their attention when it comes to public health concerns. The regular-old flu seems to be forgotten. Perhaps this effect is exacerbated by two recent flu seasons that were minimal.
Basically the message is – don’t forget about the flu. This is still a serious illness. The flu causes between 12,000-52,000 deaths each year in the US alone, and between 294,000 and 518,000 deaths each year globally. It causes more than 10 times that many hospitalizations. This is another very real concern – the total hospital burden of a tripledemic.
Get your flu vaccine. This is part of basic preventive care and health maintenance. COVID is also likely slipping into an endemic illness, and so we will likely need to get at least an annual COVID booster as well. This is now just part of routine care.
