Pfizer is developing and researching its vaccine in Connecticut.

Pfizer is already producing enough COVID-19 vaccines for up to 20 million people.

The drug maker says its 90% effective in preventing the virus. Pfizer's lab in Groton will research how safe the vaccine is.

Dr. Zane Saul, an immunologist at Bridgeport Hospital, says the numbers are impressive, but there is still a lot we don't know.

MORE: Pfizer says early data signals COVID-19 vaccine is 90% effective at preventing the virus

"The way they defined it was, 90% of the people were COVID-free after two shot[s] of the vaccine -- three weeks apart -- as compared to placebo. So those are huge numbers and great news," says Saul.

A Data Haven survey found that 20% of Connecticut residents don't plan to get a COVID-19 vaccine, and 17% said they're "not sure."

If the vaccine does get federal approval, state officials say medical workers will be the first to receive it.

Connecticut already has a draft plan to distribute a vaccine.