The need to wear masks and practice social distancing will continue long after the first delivery of a COVID-19 vaccine arrives in Maine as soon as next week, the state’s top infectious disease expert said Wednesday.

Vaccinations will have a more limited effect if Maine cannot contain the dramatic surge in cases around the state, said Dr. Nirav Shah, director of the Maine Center for Disease Control and Prevention. And, he said, even people who receive the vaccines may still harbor enough of the virus to spread it to others.

“I think we all have this hope that the arrival of the vaccine will quickly bring an end to the pandemic. I’m sorry to say that won’t happen. The end of a pandemic is not like a switch being turned off,” Shah said Wednesday. “Measures that we have all grown accustomed to – face masks and physically distancing – may not go away for some time.”

Some health experts have said mask wearing will remain a part of life through 2021, even after vaccinations are gradually rolled out to the general population.

The warnings come as Maine and other states are preparing to receive the first vaccine doses. The U.S. Food and Drug Administration is expected to grant emergency use authorization on Thursday to a vaccine developed by Pfizer. If approved, millions of doses could then be distributed around the country within days.

Maine expects to receive 12,675 doses in its first delivery, with equivalent deliveries in each of the following two weeks. The first doses will be given to front-line health care workers and residents of long-term care facilities most at risk, the state has said.

A second vaccine developed by Moderna is expected to be authorized later this month, and Maine expects to receive 34,900 doses  in the initial rounds of distribution.

Great Britain began vaccinating citizens with the Pfizer vaccine this week, the first small step in what will be a global effort to vaccinate enough people to slow, and then stop, the spread of the disease.

The Pfizer vaccine is considered to be 95 percent effective in preventing recipients from getting sick from COVID-19. The vaccine is administrated in two doses 21 days apart, although the first dose alone significantly reduces the risk of becoming ill within about 10 days of the injection, researchers say.

However, it is not yet clear if either the Pfizer vaccine or the Moderna vaccine will prevent recipients from becoming asymptomatic carriers, or silent spreaders.

That’s because the vaccines are injected in the body and act to create an immune response that will fight off the kind of lung infection that can lead to serious and life-threatening illness. Unlike vaccines that are administrated as a nasal spray, the injected vaccines may not produce enough antibodies to prevent the virus from surviving in a person’s nose. That means someone who has been vaccinated may still become an asymptomatic carrier.

More research is underway, but public health experts have said people who get vaccinated should continue to wear masks.

“Many vaccines don’t necessarily prevent you from harboring the virus. They just prevent you from getting sick from it,” Shah said Wednesday. “That is one of the reasons why the arrival of a vaccine may not spell the end of the pandemic.”

While the first vaccines could arrive next week, Maine likely won’t receive enough doses to reach the general public for many more months.

Healthy Mainers without underlying health conditions that put them at elevated risk, such as diabetes, high blood pressure and obesity, might not be vaccinated until the summer of 2021 or later, Shah has said.

Dr. James Jarvis, senior physician executive for Northern Light Maine Health, has said that even after vaccination programs are well underway, Mainers should plan on wearing masks and social distancing through 2021 and possibly into 2022. That time frame depends on large portions of the population being vaccinated and the virus showing signs that it’s under control, he said.

On Wednesday, Shah said the vaccine will slow the rate of transmission over time, like applying a break to a speeding freight train. How quickly that happens will depend on whether the virus continues to spread as rapidly as it is now, with hundreds of cases now being reported each day in Maine – 10 times as many as the state reported during the summer.

“A vaccine for COVID-19  is maximally effective if it is introduced into a community in which the virus is controlled,” Shah said. “The better we get control of the virus today, the more success we will have with the vaccine tomorrow, the next week and the next month.”