First, it was a shot or two of the COVID-19 vaccine. Then it was a booster shot after eight months, until they changed it to six, then five months. Now, federal health officials have approved another shot four months from the last if you’re at least 50 years old or in poor health.
But is it possible to overdo it with COVID-19 vaccine reminders? Could it end up like the overuse of antibiotics that medical experts are now warning breeds superbugs that resist them?
There is no evidence for this yet, say most experts. But questions of too much stimulation are fueling growing debate among scientists as a panel of experts meet April 6 to advise the Food and Drug Administration on vaccine booster doses and updates tailored to emerging variants. .
Earlier this year, the head of vaccine strategy at the European Medicines Agency, Marco Cavaleri, raised concerns that an excessive booster could weaken rather than boost our immunity.
âIf we have a strategy where we give boosters every four months, we end up potentially having immune response issues,â Cavaleri said at a Jan. 11 press conference.
Dr Sarah Fortune, a professor in the department of immunology and infectious diseases at Harvard TH Chan School of Public Health, told German news agency Deutsche Welle a week later that Cavaleri was likely referring to a possible depletion of T cells that help protect the body. of infection.
“T cells become dysfunctional when they repeatedly see the antigen in certain contexts,” Fortune told Deutsche Welle. Vaccines introduce antigens to generate an immune response. But Fortune added that studies of T-cell depletion are based on HIV or cancer patients “where the antigen is there all the time, not just repeated vaccination.”
So far, there is no evidence that repeated vaccination weakens immunity or produces resistant viral strains.
“I haven’t seen any evidence to suggest that additional reinforcement would weaken protection or breed variants,” said Holden T. Maecker, director of the Human Immune Monitoring Center at Stanford University School of Medicine. “Our knowledge of immunology generally does not suggest such weakening or overloading, as long as the vaccinations are sufficiently separated in time.”
But others have noted that much remains unclear.
“Honestly, we really don’t know,” said Dr. Michael Daignault, an emergency physician at Providence Saint Joseph Medical Center in Burbank, who noted that the US is relying on data from the second booster program that Israel just launched in January. . “I know there’s a lot of speculation, but there’s no overeating data.”
The COVID-19 vaccine booster intervals requested by U.S. health officials have little public health precedent. Many childhood vaccines are given in two to four shots from birth to age six. But other than tetanus boosters every 10 years, it’s over after that. Influenza vaccines are given annually, tailored to the strain prevalent around the world.
But it’s unclear if a number of COVID-19 vaccines will provide long-lasting protection, or if repeated booster shots will be needed, and if so, how often? Cavaleri and other health officials have argued that it is not practical to boost several times a year and that vaccination efforts should focus on preventing serious illnesses rather than reducing mild cases of “breakthrough” among the immune.
Others, like Dr. Bob Wachter, who chairs the medical department at UC San Francisco, countered that “there is a small but real risk” that a breakthrough case will lead to “long COVID” chronic illness and increases the long-term risk of mental illness, cognitive decline and diabetes. He called the risk of being overboosted “theoretical” and urged those eligible for the second booster to “get vaccinated”.
Is there a danger that overuse can weaken the effectiveness of vaccines as with antibiotics?
There is no comparison to the overuse of antibiotics, said Dr Robert Quigley, an immunologist and cardiac surgeon in Pennsylvania who is the global medical director of International SOS, a company that advises companies whose employees face medical problems traveling abroad.
“We’re talking about apples and oranges,” Quigley said. âYou cannot extrapolate from antibiotics to vaccines. The mechanisms of action are therefore unrelated and involve different fundamental scientific principles.
Antibiotics kill or suppress the growth of infectious bacteria, while vaccines use neutralized elements of disease-causing bacteria or viruses to trigger an immune response from your body.
Is there a benefit to waiting longer between reminders? The Centers for Disease Control and Prevention recently revised their guidelines for the interval between the first two Pfizer and Moderna vaccines, based on experiences in Canada and the United Kingdom that a longer interval between vaccines improved their effectiveness. in preventing disease and reducing side effects.
But the CDC said the benefits peaked at eight weeks between injections â which Daignault said is significantly less than the recommended four-month booster interval.
Maecker said the booster intervals were based on evidence of waning immunity.
“I would say there’s no reason to boost earlier than four to six months, just because there’s no real benefit to a fully vaccinated person – immunity doesn’t wane that quickly,” Maecker said. âSo for me, less than four months would be too soon. I think as long as people don’t try to boost too early, the benefit/risk ratio is very favorable. I get my boost on Sunday!