I frequently get the question from patients and listeners: “Should I take this year’s flu shot?”
I’ve long answered: “When it comes to the influenza vaccine, I’m an agnostic.”
When applied to religion, an agnostic isn’t certain there’s a God, but is not entirely convinced that God doesn’t exist, which would be the more committed stance of an atheist. An agnostic takes a position that neither believes nor disbelieves.
I’ve long felt that for me personally, family members, and for many of my otherwise healthy patients and listeners, the annual flu shot confers little protection, and may in fact have downsides that outweigh its benefits. However, I’m not unequivocally opposed to the flu shot, and if some people believe it can help them, they’re entitled to opt for it. Special circumstances may make it more likely to be a net plus, like if you’re frail, have poorly-controlled diabetes, have a heart or respiratory condition, or are immunosuppressed.
But a new study is encouraging flu vaccine skeptics, and perplexing upholders of public health orthodoxy. It’s entitled “Effectiveness of the Influenza Vaccine During the 2024-2025 Respiratory Viral Season”.
It was a study looking at whether the flu shot, administered to thousands of employees of the Cleveland Clinic, conferred protection against the flu over the ensuing 25 weeks.
Those receiving the flu shot had an incidence rate that was 27% higherthan those who did not. You read that right: the shot had a negative27% effectiveness!
Now, that was unexpected! It’s widely acknowledged that the flu shot doesn’t come close to providing universal protection—unlike other vaccines for, say, measles, which boasts a 95-97% effectiveness rate (but with new concerns arising over waning immunity). Each year’s version of the flu shot is based on a projection of what the rapidly-mutating flu shot will look like when administered months after the vaccines are manufactured. Therefore, by even the rosiest CDC estimates, it ranges in effectiveness from year to year of up to 60% (best case), to as low as 10-20%.
Most of us have experienced the disappointment of getting the flu shot and still coming down with the flu. Some people blame the flu shot for causing the flu. Health authorities keep telling us, no, the vaccine can’t give you a case of the flu, because it uses an inactivated virus. But it sure seems like that sometimes.
But this study suggests that vaccine recipients at Cleveland Clinic would’ve been better off skipping the jab altogether! How is it possible that flu shots not only weren’t that effective at conferring protection, but seemed to make it even more likely people would get the flu?
Vaccine defenders were quick to pounce. Jeremy Faust MD writes on Substack (paywalled) “Why that ‘negative effectiveness’ flu vaccine study on Fox News really, really sucks”. Seems like RFK, Jr. is living rent-free in their heads!
Critics point out, correctly, that this study was a pre-print, meaning it hadn’t yet been subject to exacting peer review like a properly published study. The scrutiny applied by journal editors can sometimes spot methodological errors—or even outright fraud—that invalidate a study’s conclusions before it becomes an accepted manuscript. Since the emergency of Covid, and facilitated by the democratization of the Internet, publication of pre-prints has been accelerated, risking rushes-to-judgement.
Admittedly, pre-prints from MedRxIv.org carry the disclaimer: “Caution: Preprints are preliminary reports of work that have not been certified by peer review. They should not be relied on to guide clinical practice or health-related behavior and should not be reported in news media as established information.”
It’s also been suggested that there were some confounders that may have made it just seem that flu shot recipients were more likely to get the flu. There’s a possibility that non-recipients of the vaccine may have shown less interest in getting tested for the flu, because, well, they’re just less concerned about the flu, or out of regret for not having taken the shot. But it could’ve worked the other way: They might have been less likely to wear masks or avoid crowds.
The study authors acknowledge that the population they studied was of mostly healthy adults of working age. Hence, it doesn’t speak to the potential efficacy of the flu vaccine for children, the elderly, or sick vulnerable individuals.
But it must be pointed out that one of the principal drawbacks of the flu vaccine is that it works least well precisely in those who might need it most—older people or those with impaired defenses. That’s why special triple-strength shots are sometimes administered to seniors. But they still show equivocal benefits because—Catch 22!—it requires a robust immune system for the shot to take.
Also, the authors of the new pre-print readily admit that they weren’t able to draw conclusions about the value of the flu shot in reducing the severity or duration of symptoms, which might be a consideration. Even otherwise healthy people can sometimes die of the flu, but unlike the deadly Spanish Flu pandemic of 1918, which indiscriminately felled young and old alike, most modern flus mostly kill the vulnerable. The CDC estimates 36,000 people die of flu each year; flu-related deaths in healthy adults aged 18-49 are extremely rare, with a mortality rate of around 1.9 per 100,000 population.
One possible explanation for the findings is particularly interesting. It’s been argued that, paradoxically, the reason some people get the flu after dutifully taking the shot year after year is because the shot is somewhat successful at preventing them from getting a natural infection, thus rendering them less able to acquire natural immunity—which, as Covid has amply illustrated, is the best way to establish a bulwark against shape-shifting respiratory viruses.
Along similar lines, some studies have raised the specter of immune system exhaustion after repeated vaccinations. In one it was found that a previous year’s vaccine attenuated the effectiveness of a subsequent flu shot:
“Immunological studies have shown that antibody responses to influenza A(H3N2) can be blunted with each additional vaccination received.”
Add to these considerations the concern that flu vaccines often contain preservatives and adjuvants, which in small amounts might be deemed safe, but with cumulative exposure or in susceptible individuals might pose risks. Multi-dose vials of the flu vaccine include thimerosal, a form of mercury (single-use vials do not require it); they also contain small amounts of aluminum salts and formaldehyde.
Whether or not the new pre-print is to be believed, it’s hardly a ringing endorsement of the flu vaccine for otherwise healthy individuals. HHS under RFK Jr. promises a sweeping reassessment of our vaccine campaigns. Merely raising questions doesn’t imply abandoning immunizations, as critics irrationally fear; we just need to leverage science to make safer and more effective vaccines and recommend them to the right people, for the right reasons, at the right times. Only then can we restore public confidence in health authorities’ recommendations.
That being said, when it comes to the flu shot for healthy adults, I remain a devout agnostic.
