Experts: Downside to Covid vaccine and flu shot together

The following is an excerpt from STAT News.

As the promotional push to get people vaccinated with one of the updated, bivalent Covid vaccines heats up, federal health authorities are urging Americans to consider getting their Covid shot and their flu shot at the same time.

And with concern about a fall wave of Covid paramount in this effort, the messaging is stressing the importance of doing this sooner rather than later.

There’s just one problem with the advice. It’s still early to get a flu shot.

The protection generated by influenza vaccines erodes pretty quickly over the course of a flu season.

A vaccine dose given in early September may offer limited protection if the flu season doesn’t peak until February or even March, as it did during the unusually late 2021-2022 season.

“If you start now, I am not a big fan of it,” Florian Krammer, an influenza expert at Mount Sinai School of Medicine in New York, told STAT. “I understand why this is promoted, but from an immunological point of view it doesn’t make much sense.”

A number of studies have shown that the benefit of a flu shot wanes substantially over the course of a flu season — exacerbating effectiveness problems that are frequently seen when some of the strains in the vaccine aren’t well matched to the strains making people sick.

Work done by researchers from the Kaiser Permanente Vaccine Study Center and the Harvard School of Public Health estimated vaccine effectiveness declined by about 18% for every 28-day period after vaccination. 

A study done by scientists at the Centers for Disease Control and Prevention and elsewhere showed that the vaccine’s protection against flu that is severe enough to trigger hospitalization decreases by between 8% and 9% per month after vaccination.

In older adults, who are more likely to get seriously ill from flu, the decline happened at a rate of about 10% to 11% per month.

If you ask someone who researches flu and flu vaccines, they will likely quietly — or in some cases, not so quietly — advise you to wait at least until the end of October to get a flu shot, though they’ll attach the caveat that if you start to hear about flu activity picking up where you live, you should fast-forward your plans.

The CDC’s official advice states that “September and October are generally good times to be vaccinated against flu,” though the agency’s website adds that “ideally, everyone should be vaccinated by the end of October.”

Noel Brewer, a professor of health behavior at the University of North Carolina, said he thinks moving to this joint-administration approach is the right idea. Covid vaccine delivery has been overly complicated, he said, requiring people to keep track of too many things. How many shots they’ve had. When they last had a shot. When they are next eligible for a shot.

People have been tuning out, he said — an assertion bolstered by the booster uptake rate.

The percentage of eligible people who got a second Covid booster is lower than the percentage of people who got a first booster, which is lower than the percentage of people who got a primary series of two shots.

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