The Middletown Press (Middletown, CT)
Third dose or booster?
Expert: The difference comes down to immunity
The difference between a third dose of a COVID vaccine and booster may be academic, but it could have an impact on future vaccination efforts, health experts said.
“It’s all value judgment, it’s not data,” said Ridgefield resident Art Caplan, founding head of the Division of Medical Ethics at the New York University Grossman School of Medicine.
Caplan said the real question is: “How much immunity do you want to get for how long a time?”
What differentiates a booster and a third dose comes down to immunity, according to Caplan. A first responder who was vacci
nated in January may see their immunity against COVID-19 waning. In that case, they might receive a third shot, considered a booster.
For some, a third dose is needed to initially get the full immunity offered by the vaccine.
But whether it’s called a third dose or a booster does matter, at least to perception. What that third dose is called may convince some patients to roll up their sleeves.
The Centers for Disease Control and Prevention said last week that anyone 65 and older is eligible to receive a “booster,” as are people 18 and older who live or work in high-risk settings, or those who are at risk of serious infection due to a medical condition.
However, many vaccines require several doses to be fully effective. HPV vaccines, for example, are three shots spaced over six months and are good for almost 10 years.
Hepatitis B is a three-dose course. Polio is a four-shot course. Tetanus shots, you get once, and they last for a decade. And flu shots are administered yearly.
“A great example is the MMR vaccine, which we give to infants, at 2 months, 4 months, 6 months of age, and then between 5 and 6 years, and then when they're around college age, they get another shot,” said Rick Martinello, director of infection prevention at Yale New Haven Health.
“We consider the first five doses to be part of their primary series,” Martinello said. “So we don't talk about that as being a booster.”
But Caplan said we don’t yet know how far to space out COVID-19 vaccines to get the best, longest-lasting immunity.
“We don’t really know the answer as to what would ideally be the best number of shots or the timing,” he said.
It may be “to really get a kick, we have to go to three shots spaced out in a certain way.”
Martinello said some researchers have postulated that the Moderna vaccine is offering longer lasting immunity simply because of its spacing.
“The speculation now is that the reason we're seeing better durability to the immunity produced by the Moderna two shots, is that Moderna is spaced apart by four weeks, whereas Pfizer is only spaced apart three weeks,” he said.
“We are still learning about how the timing of those exposures impacts the durability and the effectiveness of immunity,” Martinello said.
“With the COVID vaccine, all of them, we're not yet confident what the needs of that primary series are going to be,” Martinello said. “It may be that we really do need three shots to achieve durable immunity. In the future, once that was kind of settled, we wouldn't refer to that third shot as a ‘booster,’ we’d just say, ‘your third shot of your primary series.’”
The latest efforts to roll out additional shots to those eligible comes on the heels of a recent wave of cases brought on by the delta variant. On Tuesday, the state said the positivity rate for new COVID tests was 2.83 percent. Hospitalizations dropped by a net of five patients for a total of 259 statewide.
Experts said finishing a vaccine course is often a problem. With the HPV vaccine, for example, Caplan said “many young women don't come back for their third shots.”
“Compliance with the first dose markedly exceeds that of the additional doses in the primary series,” Martinello said of the HPV vaccine.
Some people, Caplan said, might be more likely to get a third dose than a booster.
“It’s psychologically different,” he said.
Martinello speculated the opposite. “‘Booster,’” he said, “has kind of a positive connotation, that it is boosting how well overall things are working. Whereas the ‘third dose’ may seem burdensome.”
Some, including the World Health Organization, have argued that wealthy countries should not be administering “boosters” when poorer countries haven’t yet had access to any vaccine at all.
“If you call a vaccine a ‘booster,’ that’s a little different ethically because it sounds like you had a meal and now you're having dessert,” Caplan said.
Those ethical questions are alleviated, at least somewhat, if it’s a third dose, he said.
As to why the vaccines were distributed before the correct number of doses and spacing was precisely known, Caplan said it was “because of the pandemic killing people back when we didn't have any vaccines.”
“The plague was going to kill us all,” he said. “I agree with the way they did it completely, ethically, but it left us sadly with a lot of unknowns.”