We may not reach herd immunity, but public health experts say the vaccine can still contain the COVID-19 virus

Eliza Fawcett, Hartford Courant
·4 min read

As Connecticut and the nation race to vaccinate as many residents as possible, a new reality is emerging in the fight against COVID-19: reaching herd immunity — much less completely eradicating COVID-19 — may be impossible, but the virus can be contained.

“Overall, getting to a level that will completely halt transmission with regard to SARS-CoV-2 seems maybe unrealistic,” said Dr. David Banach an epidemiologist at UConn Health. But between immunity from natural infections and vaccines, it is possible to “achieve a high level of immunity.”

“At least in the near future, COVID will be in existence and my hope is that vaccination will sort of change it from being a pandemic to something that we see in much smaller numbers and much less severity and I think the vaccines to provide that protection to prevent severe illness,” he said.

Over the course of the pandemic, public health experts have pointed to herd immunity—the level of immunity in a population, due to both infections and vaccinations, at which large viral outbreaks are prevented—as a key goal of vaccination efforts. National and state experts have said that to achieve herd immunity, at least 70% to 85% of a given population will need to be need to be immune to the virus.

But despite becoming the first state in the country Monday to reach partial vaccination for 50% of adults, Connecticut may not be able to hit that vaccination threshold, experts now say.

Still, Connecticut has seen the clear benefits of its own vaccination campaign: falling rates of COVID-19 hospitalization and mortality. Among the state’s oldest residents, deaths due to COVID-19 have rapidly declined. The number of hospitalizations has also fallen in recent weeks; the overwhelming majority of state residents hospitalized with COVID-19 are those who are unvaccinated. On Monday, the state’s weekly average for COVID-19 cases dropped to 1.9%, the lowest it has been since mid-October.

State officials have said they expect the virus to continue to exist in parts of the state where vaccination rates remain low. Gov. Ned Lamont said Monday that there will likely be periodic flare-ups of the virus, meaning that the state will have to be “very careful and also very agile” in its public health response.

“There will be pockets of people that choose not to get vaccinated, and those pockets of people will provide opportunity for COVID to continue to lurk,” Lamont’s chief operating officer Josh Geballe said. “That’s likely the mode we’re going to be in for some time. And therefore this is why we’re so focused on getting everyone vaccinated that we can, despite the fact that the cases and the test positivity and the hospitalizations are all declining so rapidly.”

Overall in Connecticut, 40% of the total state population have been fully vaccinated and 56% have received at least one shot of the vaccine. Reaching that next section of the unvaccinated population may prove challenging, officials have said, as it hinges on harder-to-reach populations and those more skeptical of the vaccine.

“It’s not an on-off. It’s not like, ‘Ah, we’re finally at herd immunity and we’ve stopped COVID dead in its tracks,” Lamont said. “50% fully vaccinated makes an enormous difference. 80% makes an even bigger difference going forward.”

Keith Grant, Hartford HealthCare’s senior system director for infection prevention, said he thought Connecticut had a “greater opportunity than most other states” of reaching a level of herd immunity, but cautioned that it remains a “very challenging” task.

Still, he said there is reason to be “cautiously optimistic.” He noted that among residents ages 65 and over — an age group which saw a high degree of mortality throughout the pandemic — deaths have largely dropped off, due to vaccinations.

Experts caution that given the global scope of COVID-19 spread, as well as the emergence of new variants and uneven vaccination rates, it’s highly unlikely that COVID-19 will be eradicated in the near-term.

Dr. Thomas Balcezak, chief clinical officer for Yale New Haven Health, said that across human history, only one infectious disease has been successfully eradicated: smallpox. It’s likely that COVID-19 will not be eradicated, instead “joining all the other diseases that plague mankind.”

“If we do not reach that 80% number, as most experts would say is the threshold for herd immunity, then what that means is that we will be living with this disease for some time to come, just like we live with many of the other diseases — influenza, for example, tuberculosis, polio,” he said.

Eliza Fawcett can be reached at elfawcett@courant.com.