Certain vaccines, such as the tetanus shot, require boosters every decade to rev up the immune system again. Some, like the flu vaccine, must be given every year because the virus changes so much.
Will something similar happen with the COVID-19 vaccines?
“Certainly, immunity will fade,” Dr. Paul Offit, an infectious disease physician and director of the Vaccine Education Center at Children's Hospital of Philadelphia, told TODAY.
“The question is does it fade to the extent that you're not protected against severe disease?”
Researchers may know in about six months whether booster shots might be needed, he added.
“Unfortunately, like so much else in COVID, it's one of those things where we won't really know when we are going to know until we have evidence that things are no longer working,” said Dr. Daniel Kuritzkes, chief of the division of infectious diseases at Brigham and Women's Hospital in Boston and professor of medicine at Harvard Medical School.
“We need the accumulated experience over time to know what it all means.”
For now, the shots are working well, with Offit calling them “powerful immunogens.” Both he and Kuritzkes predicted immunity given by the COVID-19 vaccines would last two to three years.
What’s known now:
This month, Pfizer and BioNTech said trial data showed their vaccine still offered high levels of protection against COVID-19 six months after the second dose.
Moderna also touted a study showing “antibody persistence” six months after the second dose of its vaccine.
Both vaccines are extremely effective in the real world, reducing infections by 90% in fully vaccinated people, the Centers for Disease Control and Prevention reported in March.
Studies are now underway to measure immune responses beyond six months.
How will we know boosters are needed?
A rise in breakthrough COVID-19 infections — those happening in people who are vaccinated, but who still get infected when exposed to the virus — would be a warning sign, Kuritzkes said.
People in vaccine trials are being monitored long-term by the CDC and other groups. Currently, a tiny minority of them still gets infected, 4-5%, but if that number grows, that would be a reason to recommend booster immunizations for COVID-19, he noted.
What about COVID-19 variants?
It’s possible a separate new vaccine may be needed if a COVID-19 variant that’s resistant to the current shots emerges, both Offit and Kuritzkes said.
That hasn’t happened yet, but in a recent survey of 77 epidemiologists from 28 countries, two-thirds believed it would take a year or less for the new coronavirus to mutate to the extent that most first-generation vaccines would become ineffective, requiring new or modified shots. The survey was conducted in February and March 2021 by the People’s Vaccine Alliance, a coalition of organizations and activists.
"We may have cycles where we have to keep boosting people — either boosting them with the original vaccine, which gives you enough antibodies to spill over to the variants, or develop a vaccine that's specific for one or more of the variants," Dr. Anthony Fauci said last month on MSNBC.
"The only trouble with the latter is that otherwise you may find yourself playing whack-a-mole with the variants because we have lot of different variants... what you really need to do is to get a vaccine that's potent enough and broad enough that it will overlap all of the other variants."
That's what researchers are working towards to avoid repetitive vaccination, Fauci added.
Pfizer and BioNTech said trials suggest their vaccine is effective against a coronavirus variant that first emerged in South Africa.
In March, the National Institutes of Health said that "out of an abundance of caution" it began testing a new coronavirus vaccine from Moderna designed to protect against that variant "should there be a need for an updated vaccine," Fauci explained.
“If it turns out that we have to do a better job of matching the vaccine to these emerging variants, then another round of vaccination might be needed with a vaccine that is a closer match,” Kuritzkes said.
“It would be a bit of a hybrid because it will boost antibody levels… and enhance the specificity of the immune response.”
Would new clinical trials be needed?
Not like before. In February, the U.S. Food and Drug Administration said modified COVID-19 vaccines against variants may be authorized without the need for lengthy clinical trials.
The flu shot is needed every year — would it be the same for the COVID-19 vaccine?
Not likely since the new coronavirus doesn't mutate as fast as the influenza virus does.
“Flu is in its own league,” Offit noted. “This virus is actually fairly slow in mutating.”
Still, lifetime protection from the COVID-19 vaccine won’t happen, he predicted.
Other coronaviruses cause common colds and it's pretty clear having a cold doesn’t protect you from catching another one a couple years later. That's the main reason to think a booster shot may indeed be necessary, Kuritzkes said. But at the present time, it’s unlikely that boosters will be needed in the next couple of years, he added.
How would a booster be rolled out?
Offit believed it would happen similar to the vaccine rollout, with the oldest and most vulnerable patients as well as health care workers given priority for the shot.
Kuritzkes said it would depend on vaccine supply.
“People will retain some level of immunity, so there won't be the same urgency and mad dash to get everybody boosted within some very, very narrow window of time,” he noted. “But I think we would want to see everybody get re-immunized.”