When the early Covid vaccine trial results came out, an important indicator of success couldn’t yet be assessed: durability.
Those initial studies were just three to four months — too short to determine how long protection lasts. But now, that question is gaining renewed attention as public health officials weigh the possibility of fourth doses of Pfizer’s and Moderna’s vaccines.
This week, each company asked the FDA to authorize additional boosters — Pfizer for people over 65, and Moderna for all adults. At the same time, a study published Thursday in the journal JAMA Network Open estimated that a single Johnson & Johnson shot was 76 percent effective at preventing Covid infection and 81 percent for hospitalizations for at least 180 days.
The study aligns with data from the Centers for Disease Control and Prevention showing that from late December through Feb. 19 (the most recent data available), the weekly rate of breakthrough cases was lowest among people who got the J&J shot. The rate of Covid deaths among J&J recipients, however, was a bit higher than among those who got mRNA vaccines through Jan. 29.
Together, this evidence suggests the J&J shot might have an edge in durability over the two mRNA vaccines. None of the more than 422,000 J&J recipients in the recent study got boosters during the research period, which ended in August.
"The durability was not influenced or weakened by the delta variant," said Sebastian Schneeweiss, a co-author of the study and the vice chief of Brigham & Women’s Hospital’s division of pharmacoepidemiology and pharmacoeconomics.
"We also are not saying it’s limited to 180 days," he said, noting that was just the data available, which came from insurance claims.
A spokesperson at Janssen, J&J’s pharmaceutical arm, said in a statement that "the results add to a growing body of evidence, including provisional data from the U.S. Centers for Disease Control and Prevention, indicating the Johnson & Johnson Covid-19 vaccine provides durable protection against breakthrough infection, Covid-19-related hospitalization and death."
Dan Barouch, director of the Center for Virology and Vaccine Research at Boston’s Beth Israel Deaconess Medical Center, thinks a clearer picture is emerging of the Covid vaccines' differing properties.
"The mRNA vaccines raise antibody responses very high very quickly, and then those antibody responses and protection decline quickly, necessitating multiple rounds of boosting," said Barouch, who helped develop and study the J&J vaccine. "The J&J vaccine raises antibody responses that are much lower initially and protection that is slightly lower initially, but both of those appear to be more maintained over time."
Studying durability, of course, is crucial in determining whether booster shots are needed, and when.
“I’m not an infectious disease physician, but in my mind as a consumer, as somebody who’s getting vaccinated … if you have a choice of equally efficacious vaccines, or almost equally efficacious, and one you get boosted in much larger intervals, I would prefer that," Schneeweiss said.
Just 44 percent of vaccinated people in the U.S. have gotten booster shots, according to the CDC.
"I don’t think it’s a viable public health strategy, or a desirable public health strategy, to have multiple rapid boosts every three to six months, because people probably won’t get them," Barouch said. "So a vaccine that has better durability would certainly have a benefit for long-term pandemic control."
Still, any assessment of how long vaccine protection lasts depends on what's being measured.
"If you’re asking, 'Does it lose effectiveness from preventing you from getting sick?' Pretty clear yes, and it’s disappointing," Dr. Larry Corey, an expert in immunology and vaccine development at the Fred Hutchinson Cancer Research Center, said of the mRNA vaccines. But when it comes to hospitalizations and ER visits, he added, "we have some data that at the moment most people would say is a little murky."
Corey said he’s waiting for more information before drawing conclusions.
Dr. Robert Atmar, a professor of infectious diseases at Baylor College of Medicine, said long-term protection against the worst Covid outcomes is the priority, and in that sense, "the mRNA data is still very reassuring."
Atmar pointed to a CDC study published Friday, which found that among people who got two doses of an mRNA vaccine — no booster — effectiveness at preventing mechanical ventilation and death from an omicron infection was 79 percent through Jan. 24. The median number of days after the second dose for those patients was 256.
"That’s eight-plus months, so that’s a long time," Atmar said.
Experts expect conversations about vaccine durability to remain in the spotlight as the coronavirus transitions to an endemic state.
But even as the picture gets clearer, Corey said, risk-benefit analyses will differ from person to person. In December, the CDC recommended that Americans opt for mRNA vaccines over J&J’s, because those shots showed higher effectiveness and fewer rare, serious side effects. So even if J&J’s shot does prove significantly more durable, that advantage would be weighed against other factors.
"We shouldn’t be surprised that a virus that is affecting 7 billion people needs an eclectic approach,” Corey said. “In reality, we can’t even make 7 billion of anything effectively, and we need a little bit of diversity here. So some people will find it confusing, and some will say this kind of optionality is actually needed to solve the problem."