Delta variant is the dominant COVID-19 strain. Here’s what you need to know.

Experts believe the delta variant of the coronavirus is now the dominant strain of the virus circulating in Connecticut and the rest of the United States.

The variant, first detected in India, is believed to be about 60 percent more transmissible than the alpha variant that was first found in the U.K.,which was the previously dominant variant in Connecticut and the U.S.

After an early summer lull, cases of COVID-19 have risen in every state, a trend likely fueled by delta.

The Centers for Disease Control and Prevention now predicts the variant makes up 83 percent of new cases nationwide, Dr. Rochelle Walensky, the agency's director said during a senate health committee meeting on July 20.

She called that a dramatic increase from about half of U.S. cases from earlier in July.

“In some parts of the country the percentage is even higher, particularly in areas with low vaccination rates,” Walensky said.

All three makers of the vaccines approved for use in the United States say their vaccines are effective against the variant.

Some areas of the country have seen full-blown outbreaks of infections as the variant has taken hold. In Connecticut, one of the most-vaccinated regions of the country, COVID-19 metrics have begun to tick upwards after remaining at some of their lowest points since the early summer.

Below is everything we know about the delta variant’s impact on Connecticut. This story will be periodically updated as we learn more about the variant and its potential impact on the state and region, so check back often.

How common is delta in Connecticut?

Experts believe delta is most likely the dominant strain in the state, meaning the variant makes up the majority of new cases reported in Connecticut.

In the most recent report from the Yale School of Public Health and Jackson Laboratory, both of which track variants in the state through a process known as genetic sequencing, delta made up 63.6 percent of cases sequenced in the past week.

Cases of alpha, which was previously the dominant strain in the U.S. and Connecticut, made up 27.3 percent of infections that were sequenced.

But finding the exact percentage of delta cases in the state has proven difficult in recent weeks, because overall cases of COVID-19 have been low, experts said.

Why all the concern about delta? What makes it different?

Researchers believe delta is about 60 percent more transmissible than the alpha strain that was previously the dominant strain circulating in Connecticut. That strain, which caused a second lockdown in the U.K. last fall and winter, is itself thought to be about 40 percent more infectious than the original or wild type of coronavirus that first spread around the world in early 2020.

Research has also focused on the delta strain’s ability to dodge antibodies, potentially blunting the effectiveness of vaccines, monoclonal antibody treatments or natural immunity in people who have recovered from the virus.

Do the vaccines work against it?

The makers of the three vaccines currently in use in the United States have all said their shots work against the variant.

Pfizer has said it intends to ask federal regulators to approve a third-dose booster shot, though the CDC and Food and Drug Administration have said those who have received both of their original shots currently do not need a booster. Pfizer has also said it is developing a vaccine targeting the delta variant.

A new study by New York University researchers also appeared to show the Johnson & Johnson vaccine may be less effective at combating delta. The researchers looked at how blood samples from vaccinated people responded to delta and other variants of concern, along with the lambda strain, which was first detected in Peru.

The study found the Pfizer-BioNTech and Moderna vaccines had a “high level” of neutralization against the variants, while the single-dose Johnson & Johnson vaccine had “significantly decreased neutralization.”

The study’s authors suggested those who have received the Johnson & Johnson vaccine may need a second dose “to increase protection against the variants.”

Will we have to wear masks again?

With delta now widespread in the U.S. and causing outbreaks in other nations, some areas have returned to requiring masks— including for people who are fully-vaccinated.

In May, the CDC came out with guidance saying people who are fully vaccinated no longer needed to wear masks indoors. Connecticut followed suit shortly after, dropping its outdoor mask mandate for everyone on May 1 and its indoor mask mandate for vaccinated people on May 19. The state still requires unvaccinated people to wear a mask indoors, but most businesses have left it up to the honor system.

Some locations in Connecticut, like hospitals, prisons and public transit systems, do still require people to wear a mask even if they’re fully-vaccinated. Businesses can also opt to require everyone to wear a mask.

Los Angeles County became the first area of the country to reinstate its universal mask mandate last week. That followed a similar recommendation from the World Health Organization last month.

But so far, Gov. Ned Lamont has shown reluctance to renew COVID-19 restrictions on the state.

“I don’t think we need a lot of new mandates right now ... I feel like we are in a different situation. But I will watch it, if I see a steep curve, especially with hospitalizations. That’s the metric I follow,” the governor said July 20.

He urged those still holding out to get vaccinated, saying it was now time to “stand up.”

Some experts have said people should voluntarily mask up anywhere there’s a crowd.

“My mantra’s always: do what seems right to you,” said Robert Hecht, a professor of clinical epidemiology at the Yale School of Public Health. Hecht co-authored an op-ed in the Boston Globe saying those who are not yet vaccinated should run, not walk to get their shot.

“What does it really cost to keep wearing a mask in a very public place or with people you don’t know?” he said in a July 16 interview. “To me it’s a very small gesture to make that could really be beneficial to the people who wear the masks and to everybody else they’re with.”