Expert: Herd immunity a tough goal
Conn. residents have different reasons for not getting a COVID-19 vaccine
When asked if reaching herd immunity is important, Dr. Tom Balcezak, of Yale New Haven Health, has a simple answer.
“If you don’t want people to die of this disease, absolutely,” he said.
But the question is whether it’s feasible, despite continued progress with the state’s vaccine program.
Bridget Lesizza, for example, cannot be vaccinated against COVID, according to her doctor’s advice.
“My cardiologist advised me not to get vaccinated because there wasn't enough research on patients like myself to understand how it would affect my heart,” she said.
Four years ago, Lesizza went into
cardiac arrest four times in rapid succession. It was later determined that she had brugada syndrome, a disruption of the heart’s rhythm and a dangerous fluid buildup around her heart.
“They discovered that I had gotten the flu vaccine,” said Lesizza, who owns the Reef Shack in Fairfield. “With some people when you get vaccinated, you can get a buildup of fluid around the organs.”
She’s not against vaccinations. Far from it: She has encouraged her social circle to get vaccinated. “We were joking, ‘Get vaccinated for me! Do it for Bridge!’”
In fact, Lesizza is hoping enough people in Connecticut and the United States get vaccinated against COVID-19 so she does not face the prospect of the rest of her life behind a mask.
“I’m banking on people getting vaccinated and building up the herd immunity to go on living life without a mask,” she said. “Emotionally, that would just take too much of a toll on me.”
Defining immunity
Herd immunity, or population immunity, which UConn Health’s David Banach described as a high enough level of immunity to prevent the ongoing transmission of infection, is a somewhat moving target.
“I think what we know is that immunity, at least based on neutralizing antibodies, lasts at least six months,” said Banach, an infectious disease physician and hospital epidemiologist at UConn Health. “We don't know if it's going to be six months, 12 months, 18 months, but it's at least six months.”
There are some complicating factors. Some people in and outside Connecticut will refuse to be vaccinated, and children younger than 16 are not yet eligible. Even when you add those who are naturally immune from contracting the virus with those who have been vaccinated, it might not be enough to prevent transmission of the virus.
“I think it's going to be difficult for the entire state and the entire country to achieve population-level immunity. And then, you know, we live in a global world,” Banach said. “I think getting there will be really difficult on the current trajectory.”
The number to shoot for is 85 percent. That, according to UConn computational biology professor Pedro Mendes, is how many people must be immune in a given population to prevent transmission of the virus “given the new variants that are more infective.”
“It is now much harder to estimate given that the variants are all mixing up,” he said. “So it may be prudent to say 80 to 85 percent.”
He estimates 46 percent of the state is immune, including those who have been vaccinated and those who have recovered from COVID.
“The critical vaccination level to achieve herd immunity is not exactly known, but must be in the range of 75 to 85 percent,” Mendes said. “Therefore, this is hard to achieve without vaccinating children younger than 16 (which comprise close to 20 percent of the population). Obviously, adults that refuse to take the vaccine will also make it difficult.”
Global and local
Stopping or just decreasing viral transmission is important, Balcezak said, to prevent the emergence of new, potentially more infectious and deadly variants. The more opportunity the virus has to replicate the more likely a variant will emerge that evades immunity.
“It will eventually make its way to the United States,” he said. “There is no way you can close your border to these things.”
So whether we reach global population immunity “depends on what we decide as a country and as a world,” Balcezak said.
Banach believes reaching herd immunity on a global scale, or even statewide, is unlikely anytime soon.
“Herd immunity, which is typically, classically defined as population-level immunity within a state or country, that is going to be very difficult to achieve,” he said.
But on a smaller scale, on a town-wide level, it is theoretically possible that enough people will be vaccinated to limit transmission of the virus.
“Within communities, maybe given towns for instance, they may be able to achieve a high enough proportion of immunity, that the risk of spread within that town would be quelled sufficiently,” Banach said. “There's a huge disparity in vaccine coverage between towns in Connecticut. It's pretty striking that some towns have very high levels of vaccination, over 70 percent, and other towns are much lower.”
Community-level immunity would suit Lesizza just fine.
“I live my life at the community level,” she said. “The community level is more important, because that’s how we all live.”
If not immunity then lower transmission
Success, Banach said, is not an all-or-nothing proposition. Every individual vaccination reduces the virus’ ability to transmit and replicate.
“Being able to decrease transmission doesn't necessarily require that a certain percentage of the population be immune,” he said. “I think we'll still see benefits in terms of reducing transmission as we increase vaccination. Even if we can’t achieve total population immunity, we can still impact transmission by increasing our level of immunity, particularly in certain communities.”
Balcezak is a bit more hopeful. “We are not finished in terms of our ability to vaccinate,” he said.
There are barriers to vaccination, including both hesitancy and access issues, Balcezak said, but there may be encouraging factors as well.
“Population immunity will be achievable only if we can get children to be vaccinated,” Mendes said, and there has been some progress on that front.
Some colleges are asking students to be vaccinated in order to return to campus in the fall. The U.S. Food and Drug Administration is considering proposals to vaccinate children as young as 12. There is ongoing research to examine the possibility of vaccinating children as young as 6 years old against COVID-19.
There are vaccine mandates, but also incentives. Some companies and states are offering incentives to get vaccinated against COVID. In Connecticut, some restaurants are offering free drinks. In West Virginia, the state is offering a $100 savings bond.
“It may be a combination of all of those things that gets us over that hump,” Balcezak said. “I would not be surprised if a year from now we were having a completely different conversation.”