Connecticut's positive test rate for COVID-19 was at around 2% over the past week, down from 7% last month.

Doctors at Yale Medicine say the coronavirus data in Connecticut has been trending the right way for a few weeks now, and they say vaccines are only part of the puzzle.

Yale Medicine Epidemiologist Dr. Manisha Juthani says the vaccine won't start having a widespread "herd immunity" effect until somewhere between 60% and 85% of residents are immune.

She says it's hard to tell how many people already have natural immunity from a previous infection.

"There is a theory that we may have about 100 million people in the United States that have been infected, knowingly or unknowingly, some of them asymptomatic," she said.

Dr. Juthani says good habits like masks and distancing are still the best tools for fighting the pandemic.

"We've seen what happened around the country when restrictions were loosened too early, and too quickly," she said.

Dr. Juthani says more humid spring weather may make it harder for the virus to spread and adds the winter weather we've had over the past few weeks might be having an impact too.

"I wonder if all these snowstorms are keeping people at home, and not socializing with too many others, and could that be contributing as well to the decline that we have," Dr. Juthani said, "because it's harder to meet other people, and people are less likely to be out and about when we've got storm after storm."

Gov. Ned Lamont is optimistic about the trend. He said this week that indoor and outdoor events could see their capacities raised in March.