How the delta variant came to dominate CT COVID cases
If you test positive for COVID-19 in Connecticut right now, chances are you have the delta variant.
The strain, which first emerged in India last fall, is now predominant throughout the United States. All but a small fraction of positive test kits from Connecticut submitted for genome sequencing recently were found to be the highly infectious strain, according to the Yale School of Public Health.
The delta variant, thought to be twice as transmissible as the original strain of the novel strain, beat out other variants of the virus as it rose to prominence. Those included some variants like lambda, mu and gamma that researchers believe may be able to escape the body’s immune response to the virus, potentially blunting vaccines and some treatments.
“Delta is a lot more transmissible than those other variants,”said Rebecca Earnest, a Ph.D student at the Yale School of Public Health who is studying how alpha and delta became dominant in the state.
Those other variants “might be better at, for example, evading antibodies produced by vaccination or prior infection, but delta is just transmitting faster,” she said during a phone interview. “It’s just better able to spread person to person, get into the vulnerable populations— delta’s just really beating them to the punch.”
Researchers at the Yale School of Public Health are tracking variants and are looking, in part, for anything that could sustain itself against delta.
That includes tracking the various sub-lineages of the virus collectively called delta. Right now researchers don’t see any that are more transmissible than others “but it is possible that the next variant to rise to dominance might emerge from within delta itself,” Earnest said.
Connecticut has seen three distinct waves during the pandemic, the state’s hospital data show. The first coincided with the emergence of the original strain of COVID-19 in the spring of 2020, which lasted from March through June. The second wave began that fall and stretched into the spring of 2021. The state also saw a small wave at the tail of the second from late March through May, a period that coincided with the alpha strain becoming dominant in the U.S.
The third wave, which the state is currently still experiencing, began toward the second half of July as the delta variant spread throughout the U.S.
Precisely how much the wave last fall was driven by alpha, thought to be about 60 percent more transmissible than the original strain of the virus, is the matter of some debate.
Alpha and delta certainly contributed to a rise in COVID-19 cases, said Dr. Ulysses Wu, chief epidemiologist for Hartford HealthCare, but he also attributed the waves to social behaviors and even the weather. Last winter and during the start of the first surge 20 months ago, the colder weather kept people indoors where transmission is more likely, he said.
Alpha was the most commonly found variant in Connecticut through much of the spring, the Yale data shows, but other variants were also circulating alongside it.
“The question is ‘well what about delta?’ That’s happening during the summer,” Wu said. “That, I think, is mostly variant related, but we also had a very hot and wet summer as well so I think a lot of people were also staying inside for air conditioning.”
Delta made up all of the cases of COVID-19 genetically sequenced in the last three weeks in Connecticut, according to the latest report from Yale.
The availability of vaccines may have also inadvertently caused infections to spread, as people threw caution to the wind and the state reopened. Connecticut’s indoor mask mandate ended on May 19, the same day bars were reopened.
Those who were vaccinated took their masks off and returned to social behaviors that increased the risk of transmission, Wu said. Meanwhile, those who were unvaccinated – maybe experiencing a kind of fear of missing out – piggybacked on those who got the vaccine “and their ‘freedom’ that they were able to do,” Wu said.