Herd immunity by summer within reach
But experts warn inequities in vaccine distribution could leave some Connecticut towns vulnerable
After a year of restrictions and isolation, Connecticut may be able to reach herd immunity against COVID-19 as soon as late summer or early fall — but experts warn inequities in vaccination rates may leave some towns vulnerable to outbreaks while others are protected from them.
To achieve herd immunity — the level at which outbreaks are prevented because a large proportion of residents is immune to the virus — Connecticut will likely need to vaccinate between 70% and 85% of its population against COVID-19, said Dr. Pedro Mendes, a computational biologist at UConn Health. At current vaccination levels, that could happen sometime around August, he projects.
Connecticut has so far fully vaccinated at least 8.07% of the population and has administered the first of two doses of the COVID19 vaccine to at least 15.5% of the population, according to state data available last week.
Mendes believes that Connecticut could reach herd immunity by late summer if it administers at least 10,000 second doses a day. In his calculations, Mendes only considers second doses, given that they are the standard for full COVID-19 vaccination.
“If we were vaccinating at 10,000 per day, we’d be reaching herd immunity by August,” Mendes said.
According to Josh Geballe, Gov. Ned Lamont’s chief operating officer, Connecticut regularly administers more than 10,000 second doses per day — and on one day recently, as many as 15,000 second doses.
Mendes’ timeline aligns with forecasts from Bloomberg’s
“It is a local phenomenon. You can achieve herd immunity in a rich, white neighborhood, and a neighboring community could have no effect of herd immunity.”
COVID-19 vaccine tracker, which projects that based on Connecticut’s current vaccination rate of 21,218 first and second doses administered per day, it will take about six months to cover 75% of the population with a two-dose vaccine. That means that a level of herd immunity could be reached by September.
In his initial calculations, Mendes determined that Connecticut would only need to immunize 69% of the population to reach herd immunity. But he came to that figure before the emergence of the B117 variant of COVID19, first discovered in the United Kingdom, which is more transmissible than other common strains and has appeared in at least 42 cases in Connecticut. Mendes now estimates that the threshold for herd immunity in Connecticut is higher, somewhere between 70% and 85%.
That’s also the range that Dr. Anthony Fauci, President Joe Biden’s top infectious disease expert, has estimated that the United States population must reach in order for some semblance of normalcy to return to day-to-day life.
Even as vaccinations ramp up in Connecticut, Mendes cautioned that the rate of vaccine distribution is not necessarily constant.
“It all depends upon supply and demand,” he said. “At some point, everyone who wanted one will have it, and we’ll have to convince the other people who might be skeptical or haven’t gotten it.”
— Howard P. Forman, professor of radiology, economics, public health and management at Yale University
Possibility of inequity
The state’s accelerated vaccination plan is, in many ways, an effort to reach herd immunity as soon as possible.
In revising the state’s vaccination strategy to be age-based, Lamont has prioritized an accelerated, simplified rollout of vaccines: as he said last week, “My goal is to get as many people vaccinated as quickly as possible.” According to the state’s timeline, by early May, all residents at least 16 years old should be able to schedule a COVID19 shot.
But already, vaccination rates have significantly differed between communities across the state, often fractured along racial and socioeconomic lines. So far, white residents have been vaccinated at a significantly higher rate than residents of other racial and ethnic groups.
As of last week, at least 39% of white Connecticut residents 65 or older had received at least one vaccine dose, compared with 27% of Hispanic residents, 26% of Asian residents and 21% of Black residents in that age group.
These disparities are location-specific, with many of the state’s leastwhite and poorest municipalities — Hartford, Bridgeport, New Britain and Waterbury — reporting the smallest share of their residents with at least one dose of the vaccine, compared to all of Connecticut’s municipalities.
Those inequities could be felt acutely as the state emerges from the crippling effects of the pandemic.
Herd immunity does not only occur on a statewide, national or global level, experts say; it can be attained on the level of an individual town, so long as a community has relatively low migration into and out of it.
Howard P. Forman, a professor of radiology, economics, public health and management at Yale University, noted that if East Hartford were, theoretically, to reach a herd immunity threshold of 80%, there would still be some risk of COVID-19 infections for residents, but large outbreaks would be prevented.
However, given the uneven distribution of vaccines across the state, it’s possible that some towns could reach herd immunity well before others, giving rise to a system in which some towns are vulnerable to outbreaks while others are protected from them.
Forman said that the potential for further inequity is concerning and requires increased efforts to make vaccine distribution equitable across the state.
“It is a local phenomenon,” he said. “You can achieve herd immunity in a rich, white neighborhood, and a neighboring community could have no effect of herd immunity.”
Complicating factors
Forecasts about herd immunity are complicated by the fact that it’s still not clear how long COVID-19 immunization lasts and to what extent new, more dangerous strains of the virus will fuel the spread of the pandemic.
Forman cautioned that it may not be possible to achieve full herd immunity from COVID-19 if the transmissibility of the virus significantly increases due to new variants.
It also remains to be seen how well vaccines halt transmission of the virus from one person to another — and how long immunization actually lasts. The clinical testing for the vaccines focused primarily on their ability to prevent serious disease and death — and research on longterm COVID-19 immunity is still underway. The Centers for Disease Control and Prevention recommends that people who have been infected with COVID-19 should still get vaccinated because the length of immunity remains unknown.
“If the vaccines themselves don’t reduce asymptomatic spread nearly as much as we wanted them to, then we don’t get herd immunity,” Forman said. “It’s very possible you don’t get official herd immunity.”
Mendes noted that scientists are still researching how long immunization lasts, whether it be from a shot of the COVID-19 vaccine or a COVID-19 infection that leaves protective antibodies. Long-term protection from COVID19 could require regular vaccines or booster shots, for instance.
Despite these uncertainties, he emphasized, rising rates of immunization across the state will correlate with reductions in COVID-19 hospitalizations and deaths.
“Even when you don’t get to herd immunity — let’s say herd immunity was 80% — by the time you get to 65%, the level of infection in the community is already much lower,” Mendes said. “And we’ve started to see that already in the nursing homes.”