Scientists have found indications that the world’s leading COVID-19 vaccines offer lasting protection that could decrease the need for frequent booster shots, but have warned that more research is needed and that virus mutations are still a wild card.
Critical studies are underway, and evidence is growing that immunity from mRNA vaccines made by Pfizer and Moderna does not depend solely on antibodies that decrease over time. The body has overlapping layers of protection that offer a backup.
Pfizer and Moderna have been feeding reinforcement demands estimating that people may need annual strikes, as with flu vaccinations, and companies are working to get some candidates ready this fall. But companies won’t decide when boosters are used. This will be up to the health authorities of each country.
Other experts say boosters may be needed only every few years.
“I would have been surprised if we needed an annual booster shot,” said Dr. Paul Offit, a vaccine specialist at the Philadelphia Children’s Hospital who advises the Food and Medical Administration.
They have indicated ways that the immune system remembers the coronavirus so that once the original antibodies are gone, the body’s defenses can be put back into action if a person is exposed again.
“I’m pretty optimistic. I wouldn’t rule out the need for boosters, but the immune response now looks really pretty impressive,” said John Wherry, an immunologist at the University of Pennsylvania.
Antibodies that form after vaccination or natural infection decrease naturally, but there is evidence that those levels remain strong for at least six to nine months after mRNA vaccination and perhaps more. They also seem effective against disturbing virus mutants, at least for now.
Scientists do not even know what is called the protective correlate, the level below which antibodies cannot defend the coronavirus without additional help.
Dr. Anthony Fauci, the U.S. government’s first expert on infectious diseases, told a Senate subcommittee last week that vaccine protection would not be endless.
“I imagined we would need, at some point, a reinforcer,” Fauci said. “What we understand now is what interval it will be.”
To date, 62.8% of the adult population of the United States has received at least one dose of a COVID-19 vaccine and 133.6 million, or more than 40 percent, are completely vaccinated. The rate of new vaccinations is slowing to an average below 600,000 per day, according to the Centers for Disease Control and Prevention. It closes at 70% of President Joe Biden’s goal with at least one inoculation by July 4th.
Infections and deaths continue to decline. The nation’s seven-day average for new daily homes fell to less than 17,300 Tuesday, up from more than 31,000 two weeks ago. Daytime deaths decreased to 588, from 605, according to data from Johns Hopkins University. In all, the virus has killed more than 595,000 people in the United States
The so-called long-lived plasma cells are one of the body’s backups. Immunologist Ali Ellebedy at the University of Washington in St. Louis found that almost a year after people recovered from mild COVID-19, those plasma cells had migrated to the bone marrow where they continued to secrete antibodies. That is why even if the antibodies decrease over time, they do not disappear.
Now Ellebedy hunts the same cells at the vaccine’s recipients, and while the search isn’t over, she finds traces that are forming.
An even more important backup system comes in the form of memory B cells. If existing antibodies aren’t enough to stop the coronavirus, memory B cells are ready to scan a large number of new antibodies, Ellebedy explains. Numerous studies have found those memory cells after COVID-19 vaccination.
And if the virus causes it to pass those defenses, yet another immune branch – memory T cells – jumps out to eliminate infected cells and prevent serious disease.
With several coronaviruses causing common colds, people tend to get infected again every two to five years, Wherry said.
Based on natural immunity against those related viruses, “we’re kind of waiting for our immunity to drop,” he said. “But we don’t know. For these mRNA vaccines, we can be better off by nature, better off by a natural infection.”
To date, health authorities agree that the most common COVID-19 vaccines in the United States and Europe protect against virus mutations that are currently in circulation, though not as strong as they are protected from the original virus. .
Why? Vaccines mimic the protein that covers the outer surface of the coronavirus, and only certain points of this protein mutate, said Dr. Peter Marks, head of FDA vaccines. In particular mRNA vaccines increase antibody levels after the second dose. Those levels are so high that they offer some protection even when the vaccine and the variant are not a perfect match.
With so many people not even being vaccinated, the opportunity abounds to happen more mutations. The biggest sign that a booster might be needed would be a jump in COVID-19 cases in fully vaccinated people, particularly serious diseases and especially if infections are caused by a new variant.
To prepare, people vaccinated a year ago as part of the first Pfizer and Modern vaccination trials are now enrolled in additional vaccine studies – both a third dose of the original and versions that have been updated to suit an emerging variant for the first time in South Africa. Modern says the preliminary results are promising. More results are due this summer.
The National Institutes of Health has also begun testing a system in which patients are given a different brand of booster than their original vaccine, to see if it is effective.
Most of the world’s population has not yet received a first dose. With different countries using different types of vaccines, decisions on booster shots can vary greatly. Already, the United Arab Emirates has offered a third dose to recipients of a Chinese-made coup, the first formal introduction of any kind of booster.
If eventually boosters are called for, they won’t be needed all at once because the antibodies will gradually disappear instead of disappearing suddenly.
“Even if we need boosters or we get to the point where we see that immunity decreases a bit, we will still be much better than we were a year ago,” Wherry said.