Healthy people should get annual COVID-19 boosters to prevent widespread outbreaks, a new study from Yale University suggests.
Yearly shots provide just enough frequency to prevent huge outbreaks, while not putting an undo burden on people.
“There seems to be an inflection point” at about a year, said senior author Jeffrey Townsend, a biostatistician and evolutionary biologist at the Yale School of Public Health. “Delaying boosting beyond that point rapidly increases the risk of an infection.”
While federal officials have suggested annual shots, this study is the first to examine the long-term outcomes from a booster schedule and the first to show that boosters will be especially effective at intervals of no more than a year.
The study, published earlier this month, focused on people with healthy immune systems. Townsend and his colleagues are starting work on a similar study looking at the optimal vaccine interval for people with weakened immunity from cancer treatment and other health problems.
What the study found: Annual shots prevent 75% of infections
The researchers modeled antibody levels against the virus that causes COVID-19 if someone was boosted with a Pfizer-BioNTech or Moderna vaccine every six months, one year, 18 months, two years or three years over a six-year timespan.
Boosting twice a year reduced infections by more than 93%, the team found, but Townsend said it’s just not realistic to ask people to get vaccinated that often.
Annual shots prevented 75% of infections, while waiting six more months reduced the rate of protection to just 55%. Shots every three years prevented just 24% of infections, the study found.
“Delaying the administration of updated boosters has bleak repercussions,” it concluded.
Boosters won’t prevent all infections
For healthy people, “annual boosting really makes a difference,” said Alex Dornburg, an expert in bioinformatics at the University of North Carolina Charlotte and study co-author.
Roughly 3 in 10 people will get infected with COVID-19 even with an annual shot, Dornburg said. But 9 in 10 will be infected without such updates.
Not getting boosted triples the risk for infection over six years, co-author Hayley Hassley of Yale added.
The Centers for Disease Control and Prevention and most infectious disease experts encourage people of all ages to get boosters.
The booster has to keep evolving, too
The virus continues to evolve, “so we need to continually evolve the booster and keep it updated to the most prevalent variant,” Hassley said.
Over time, people will lose the ability to respond effectively to the virus without boosters or re-infections, Townsend said.
The latest booster is directed at both the original virus and the BA.4 and BA.5. Although these are not the most common variants anymore, the researchers said the new booster is close enough to provide a benefit.
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Getting vaccinated vs. being infected
The COVID-19 vaccines have side effects, making people feel miserable for a day or two. But an infection can be much worse, Dornburg said.
In his own case, he felt terrible for two days after his first round of shots. When he caught COVID-19, though, his lungs hurt for weeks and he was winded climbing a single flight of stairs.
“It was awful,” he said. “That calibrated me a little bit differently.”
Catching COVID-19 does provide protection against future infections, but like the vaccine, this fades over time, at roughly the same pace, Townsend said.
And it’s better not to get infected at all.
“You can’t end up in the hospital for an infection you didn’t get,” Townsend said.
In another study published Wednesday, researchers from the World Health Organization examined 26 earlier papers and concluded that people who are vaccinated or infected remain better protected against severe disease a year later, compared to those who are unvaccinated and never infected.
A year after someone is both vaccinated and infected, they have a 95% reduced risk of getting severe COVID-19 or needing to be hospitalized, the study showed. Someone infected a year ago but not vaccinated had a 75% reduced risk.
Getting infected and vaccined reduces the chance of reinfection a year later by 42%, with someone who was infected but not vaccinated had a 25% lower chance of reinfection.
When will we have better vaccines?
Unfortunately, said Dr. Eric Topol, founder and director of the Scripps Research Translational Institute, the federal government has lost its previous momentum on vaccine development.
“We need durable vaccines that would last multiple years against all variants,” said Topol, who was not involved in the new research. “We’re not getting the traction we need on these science projects. There’s not the will, the resources, the priority.”
That means if a worse variant arises at some point, the U.S. “will have to be reactive instead of having all this ahead of time – and that would be really sad because we know the path to getting ahead of the virus and we’re not doing it,” he said.
Topol thinks nasal vaccines are needed to prevent more infections. Even if a nasal vaccine has to be given more often than shots, people won’t mind as much.
“I’m excited about it. I haven’t seen anything to negate it,” he said. “I’d be happy to take a spray every few months to prevent infection.”
Contact Karen Weintraub at kweintraub@usatoday.com.
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