US officials are weighing whether to offer people who are at high risk of severe Covid-19 the chance to get another bivalent booster, according to a source familiar with the deliberations, who asked not to be named because they were not authorized to share the details of ongoing discussions.
While most Americans have gladly put pandemic precautions -- including vaccines -- in the rear view, some who are trying to protect themselves or their loved ones from severe illness have been anxiously wondering how soon they can get another shot.
One of them is Michael Osterholm, who directs the University of Minnesota's Center for Infectious Disease Research and Prevention.
The 70-year-old was quick to get an updated bivalent booster when they were rolled out in the US last fall. The bivalent booster is now recommended for all Americans 5 and older at least two months after their last dose of a vaccine or three months after a Covid-19 infection.
In February, roughly six months after his previous booster, Osterholm asked about topping off his protection with a second bivalent shot, but "I was turned down," he said.
Studies of the effectiveness of the Covid-19 vaccines show that their protection against infection, emergency room visits and hospitalizations fades after six months as levels of neutralizing antibodies in the blood fall. Some protection is left in B-cells and T-cells, components of the immune system that retain a memory of past invaders, though the duration of that protection isn't fully understood.
Last week, Osterholm caught Covid-19 for the first time.
"I have no idea how I caught it," he said. "I was wearing N95s [masks], the whole nine yards."
Osterholm knows that even if he had been able to get a second bivalent booster, he still might have gotten sick -- the Covid-19 vaccines don't provide the kind of sterilizing immunity required to block infections completely -- but he can't help but wonder whether he might have bounced back a little faster.
"I wonder what this would have been like if had gotten it," he said.
As the virus that causes Covid-19 has evolved, it has outsmarted every available kind of passive immunity, the antibodies doctors once gave vulnerable people to augment their own immune defenses. This makes vaccines one of a shrinking number of safeguards left for people at highest risk of severe Covid-19 infections.
Protection from bivalent boosters may be waning
The bivalent vaccines include two kinds of instructions to help the body fight off Covid-19. The first shows it how to recognize the ancestral strain of Covid-19, which is no longer circulating. The second set helps it better recognize and attack the Omicron virus and its descendants.
Data collected by the US Centers for Disease Control and Prevention shows that the vaccine update has boosted protection.
People who get the shots are 14 times less likely to die than unvaccinated people and three times less less likely to die than vaccinated people who didn't get the bivalent booster.
A group of experts that advises the US FDA on its vaccine decisions recommended in January that the agency phase out the monovalent vaccines, which protect only against the ancestral strain, and give bivalent doses for first shots to Americans who haven't had their first Covid-19 vaccines, a group that would primarily include babies and toddlers.
Although the bivalent vaccines have been helpful, new data suggests that just like the boosters that came before them, their protection may be starting to drop off.
In the first two months after adults get the updated booster, the shot appears to be about 50% more effective at preventing hospital or emergency room visits because of Covid-19, on top of the little protection remaining from previous shots.
By four months, however, the added protection from bivalent vaccines for those same measures falls to a little more than 30%, according to data presented at the February meeting of the CDC's Advisory Committee on Immunization Practices.
Citing this trend, the United Kingdom and Canada have begun allowing certain people to get another bivalent booster.
In February, the UK's Joint Committee on Vaccination and Immunizationrecommended that additional bivalent boosters be offered at least six months after a prior dose to adults 75 and older, seniors who live in residential care homes and anyone over the age of 12 who has suppressed immune function.
The Public Health Agency of Canada said adults may be offered an additional bivalent shot if they are older, live in residential care, or are over the age of 12 with a condition or treatment that impairs their immune function.
In fact, US officials are still trying to persuade the majority of Americans to consider getting even a first bivalent shot. Only about 54 million Americans -- less than 1 in 5 of those who are eligible -- have received a bivalent booster since the government rolled them out in September.
The US Food and Drug Administration's emergency use authorization for the bivalent vaccines doesn't allow doctors to prescribe another booster for vulnerable people or for the CDC to recommend one.
"We continue to closely monitor the emerging data in the United States and globally, and we will base any decision on additional updated boosters upon those data. Importantly, individuals who have not yet received an updated (bivalent) booster are encouraged to speak with their health care provider and consider receiving one," an FDA spokesperson said in an email to CNN.
There are several ways the agency could loosen restrictions on the use of the bivalent vaccines.
The first is to fully approve these dual-strain shots. On February 24, vaccine maker Pfizer asked the FDA to do that by submitting a supplemental biologics licensing application. Moderna has not announced a similar move and did not respond to a request for comment.
If the FDA grants that application, it will give the CDC flexibility to change its recommendations for the use of the boosters, offering doctors permission to give another dose to vulnerable patients.
Vaccine manufacturers could also ask the FDA to tweak its emergency use authorizations to include so-called permissive language that would allow for a second bivalent dose.
Osterholm said whatever mechanism the FDA uses, he strongly support giving people the flexibility to get another booster dose if their doctors feel like they need it.
Waiting on spring boosters
Some people are eagerly awaiting the chance to get another dose.
"This is absolutely currently the most frequently asked question I get," said Dr. William Schaffner, an infectious disease expert at Vanderbilt University. "It's on the mind of that segment of the population that's thinking about this very, very carefully."
He doesn't see spring boosters on the horizon in the US, however.
"Neither the FDA or CDC's Advisory Committee on Immunization Practices will make recommendations without data," Schaffner said. "And no one is collecting data now on yet another bivalent booster, as regards either the effectiveness or safety of that."
Other experts think the FDA should make it easier for people who want another bivalent Covid-19 booster to get one.
"One of the disappointments about the mRNA vaccines is that they're not holding up as well as we'd like for reasons that I think we don't entirely understand," said Dr. Peter Hotez, dean of the National School of Tropical Medicine at the Baylor College of Medicine in Houston.
"But that is the reality, and as long as that's the reality and as long as Covid is still around, I think we should be advocating for it," Hotez said, adding that he'd like to see the shots available to adults age 50 and older, not the 65 and older group that the FDA is reportedly considering.
"The doses are there, and if we don't use them soon, they're going to have to be thrown out. So better to give them to people who are all in and willing to take it than just the tossing, right?" Hotez said. "So I think the FDA and CDC will say something pretty soon. That's my guess, that there's been enough are out there in the public domain that I think we'll hear from them pretty soon on this."
Others worry that the offering more boosters to the elderly and immunocompromised might wind up giving them a false sense of security but little extra protection.
Because age diminishes the body's ability to respond to vaccines and people with weakened immune function also don't tend to see big increases in protection after vaccination, Dr. Yvonne Maldonado, a professor of Global health and infectious disease at Stanford University, wonders how much good a change in policy would actually do.
"In that situation, I just don't know if additional boosters are going to make a difference, because we know for a lot of those people, their immune responses are not going to be great," she said.
On the other hand, she says, Covid-19 still hasn't settled into any predictable pattern that would help health officials know whether they're giving another round of shots at the best time.
"If this were a seasonal virus, I would say we're all good because it would only show up once a year, but we just haven't developed a real pattern of circulation for this virus. So it is a little risky to go through the next few months waiting for a fall booster," Maldonado said.
