Why health experts say COVID boosters will be the future

While only about half of Connecticut’s population has received a single dose of the COVID vaccine, there is already discussion about booster shots.

Pfizer’s Angela Hwang said this month that immunity granted by her company’s vaccine lasts at least six months, and so far it’s effective against emerging, more infectious variants. But, she said, booster shots will likely be necessary.

“What we know today is that we have a highly effective vaccine that is safe, that the duration of protection as we know it is six months,” she said. “This next study will help us to understand what are the time intervals by which you need to boost — at six months or at 12 months?”

Ohm Deshpande, who runs Yale New Haven’s vaccine program, described it as a race. Can we vaccinate everyone and achieve population immunity — a state in which the virus cannot transmit from person to person — before immunity runs out?

“If large portions of society don’t get vaccinated, it creates a pool for viral replication and mutation, which could be very dangerous,” Deshpande said. “The quicker we vaccinate as many adults as we can, and then the 20 to 25 percent of society under the age of 16 when the vaccines are approved, the less likely we will need vaccine boosters.”

Vaccine boosters are not uncommon, according to David Banach, an infectious disease physician and hospital epidemiologist at UConn Health.

“In terms of existing vaccines, like pneumonia vaccines, after five years or so, we get repeated pneumonia vaccines,” he said. “Even the childhood vaccines are multiple doses to be given over time. Very few of them are single-dose vaccines. The single dose for a lot of those vaccines can get short-term immunity. But if you really want to get longer lasting immunity, there's boosting involved.”

But it remains unknown what those COVID-19 vaccine boosters will do.

“That's something that we also have to be aware of, if boosters are either going to be directed toward addressing changes associated with variants, or if the boosters would be directed toward bolstering existing immunity, because immunity wanes over time,” Banach said.

It does not appear to be a situation similar to the flu vaccine, which patients are encouraged to get annually.

“With flu, we use the term ‘genetic drift,’ significant changes to the flu that you need to base our adaptation of the vaccine on in order to provide protection,” Banach said. “Right now, it doesn't seem like that sort of virus-vaccine relationship is there for SARS-CoV-2.”

There may, however, be variants that evade the immune response granted by vaccines. Deshpande said reaching herd immunity is the key to stopping the generation of those variants.

“The quicker we reach herd or population immunity, the less likely we will have variants that necessitate a booster,” he said. “Viral variants arise through viral replication. Vaccination prevents viral replication.”

However, Banach argued the world may never be truly free of COVID-19.

“In the scientific community, there's a strong consensus that we won't be able to eradicate the virus entirely,” he said. “With our current measures and vaccines in terms of global eradication, we think about that with other kinds of infections, things like polio and smallpox. But the general feeling is that we won't be able to achieve that with this virus, at least in the near future.”

There may be periods of time with no cases of the coronavirus in Connecticut and in the United States, but Banach said reaching global population immunity with highly infectious respiratory diseases is difficult.

“Here in the U.S., especially in Connecticut, our vaccine coverage is very high,” he said. “But for us to achieve that across the entire world, I think it's a difficult or unrealistic expectation.”