Your questions about the new COVID-19 vaccines, answered

Who gets it first? What are the side effects? What should I do if I’m pregnant?

The first patient enrolled in Pfizer's COVID-19 coronavirus vaccine clinical trial at the University of Maryland School of Medicine in Baltimore on May 4, 2020.Associated Press

Sometime this month, the first Massachusetts residents could begin to get vaccinated against COVID-19, hopefully signaling the start of the end of the grueling pandemic. But the record-time arrival of these vaccines raises a host of questions from a wary and beleaguered public: How bad are the side effects? How long will immunity last? Will I have to keep wearing a mask after my shots?

The Globe reached out to public health authorities in Boston and across the country to tell readers what the experts do — and don’t — know about the vaccines that hundreds of thousands of us will be receiving in the coming months.

Who will get the vaccine first?

Health care personnel — including doctors, nurses, cleaning staff, clerical workers, and food service employees — will have access to the vaccines first, along with residents and staff of long-term-care facilities. Governor Charlie Baker made his priorities clear in a press conference Thursday at the Worcester field hospital, saying, “Health care workers and long-term-care folks are absolutely going to be up near the top of the list.” The state has until Friday to submit its vaccine distribution plan to federal authorities. Baker said more details about the plan would come Monday.

How many people will get the vaccine in the first phase?

If Pfizer’s application for emergency use is approved next week, Massachusetts expects to receive an initial shipment of 60,000 doses, and up to 300,000 doses by the end of the year or first week of January, once Moderna’s emergency-use authorization is granted, said Dr. Paul Biddinger, director of emergency preparedness at Massachusetts General Hospital and chairman of Baker’s vaccine advisory group. (The numbers represent the first doses of the two-dose regimen. The government’s federal allocation system will automatically deliver the second dose, according to Biddinger.)

Even Baker predicts the rollout “will probably be a little lumpy” as distribution gets up and running. “Because there are definitely more than 60,000 health care workers and residents of long-term-care facilities in Massachusetts, I think there’s going to have to be a degree of subprioritization,” Biddinger said, “both potentially at the state level and potentially at the hospital level, just because there won’t be enough vaccine for everyone on day 1.”

I’ve heard the Moderna and Pfizer vaccines require two doses. Do I really need both shots?

Indeed, both Moderna’s and Pfizer’s vaccines require two shots, administered 21 and 28 days apart, respectively. Dr. Daniel Kuritzkes, chief of the division of infectious diseases at Brigham and Women’s Hospital, noted this two-dose regimen is not uncommon for vaccines. The hepatitis A vaccine, for example, is given in two shots, spaced at least six months apart. Some young children need two doses of the seasonal flu shot.

And yes, you need both doses to develop enough antibodies to fight off infection.

“We know from the early phase studies of these [COVID-19] vaccines that you get some antibodies made after the first vaccine, but you don’t really get the high titers of antibodies that we think are necessary to be protective until after the second shot,” Kuritzkes explained.

The downside to the two-dose regimen, of course, is that some people may not get both shots. Crucially, doctors and pharmacists will have to educate people on the need to return for their second dose, said Dr. William Schaffner, a preventive medicine and infectious diseases professor at Vanderbilt University School of Medicine. Otherwise, he said, “they won’t be optimally protected.”

I already had COVID-19. Do I still need to get vaccinated?

“Probably yes,” said Dr. David Hamer, an infectious disease specialist at Boston Medical Center. We still don’t know how long immunity to the coronavirus lasts, either from natural infection or vaccination. “There have been a few cases of reinfection,” Hamer noted, “but it seems to be a rare event.”

Dr. Philip J. Landrigan, director of Boston College’s global public health program, said “there’s no downside” to getting vaccinated even if you’ve recovered from COVID-19. But the vaccines initially will be in limited supply, he said, so there’s no need to rush to the front of the line. Dr. Karen Tashima, director of clinical trials in the Immunology Center at Miriam Hospital in Providence, agreed.

“Maybe people had COVID in the last six months and don’t need [the vaccine],” she said. “But they might need it if their antibodies [eventually] go away.”

After I get vaccinated, do I still need to wear a mask and social distance?

Yes, and for many reasons, according to public health experts. For one, we don’t know whether the vaccines will prevent infection and transmission of the virus. All we know is that they should keep you from getting sick.

“It takes two weeks after your second shot to get good immunity. But there’ll still be a lot of infection going around. After you get the vaccine, you’ll still have a 5 percent chance of getting the virus,” Tashima said. “And the studies haven’t shown yet that you can’t spread the virus asymptomatically after you’ve been vaccinated.”

Masking and social distancing will continue, said Kuritzkes, “at least until we see substantial reduction in community prevalence and incidence of COVID-19.” Plus, following public health guidelines is good manners.

“What you really want is to have sufficient solidarity,” said Bill Hanage, an associate professor of epidemiology at the Harvard T. H. Chan School of Public Health, “so even once you’ve received the vaccine, you’re gonna be wearing a mask, so that other people can feel comfortable wearing a mask around you.”

What are possible side effects to these vaccines?

Don’t be surprised if you experience unpleasant side effects. Fatigue, soreness at the injection site, muscle aches, and low-grade fever are the most common reported side effects in the Moderna and Pfizer vaccines. Those are signs of the body’s immune response and should resolve after one or two days, experts said.

Clinical trials showed the reactions are usually stronger after the second dose, and worse for younger people, according to Schaffner, due to their robust immune systems.

“It’s short-lived, but you might feel crummy the next day,” Tashima said. “After the second shot, you might consider not going to work the next day.”

OK, so I got vaccinated. Will I have to get vaccinated again next year?

We just don’t know yet because we don’t have any long-term studies. “People might need a booster shot in six months, a year, three years. We do not yet have any data on how long the efficacy of the vaccine will last,” said Dr. Dan Barouch, director of the Center for Virology and Vaccine Research at Beth Israel Deaconess Medical Center.

I’m pregnant and/or breastfeeding. Can I get the vaccine?

There’s no easy answer here. The clinical trials so far have excluded pregnant and breastfeeding individuals, so we don’t have any relevant safety data yet. Kuritzkes said pregnant and nursing women should consult with their obstetricians.

Can my kids get the vaccine?

Yes, but not anytime soon, according to Kuritzkes. “I don’t think the vaccine will be made available to children until there are other data about safety and immunogenicity,” he said.

Pfizer began testing the vaccine it developed with the German biotech BioNTech in children as young as 12 in October. Cambridge-based Moderna confirmed Wednesday that it plans to start doing the same with its experimental vaccine. Moderna’s study, which will involve an estimated 3,000 adolescents, was posted Wednesday on clinicaltrials.gov but has not begun recruiting volunteers.

“The hope is that children will be able to be vaccinated in 2021 before the next school year starts,” Barouch said.

We’re about to start vaccinating hundreds of thousands. Are people worried things could go wrong?

Managing the logistics will be formidable, and many details of the state’s plan have not yet been made public. But Biddinger, of Baker’s advisory group, hinted at some of the complexities officials are wrestling with.

Health care systems will have to stagger how they immunize their employees because some may experience the vaccines’ side effects. Then there are the vaccines themselves: Pfizer’s have specific storage directives only larger hospitals may be able to handle. The vaccines, which must be kept at minus-70 degrees Celsius, are packed in dry ice and shipped in 1,000-dose trays known colloquially as “pizza boxes.” Pfizer’s specialized shipping containers can temporarily store the vaccine trays for up to 15 days when replenished with dry ice.

”Small community health centers or individual practices or even smaller hospitals might not necessarily be able to use 1,000 doses right away as effectively,” Biddinger said, “so there probably will be different products sent to different entities based on their size and their capabilities.”

How many people need to be vaccinated to achieve herd immunity?

To quash the pandemic, infectious disease experts believe between 60 and 70 percent of the population must become immune, either through vaccination or natural infection. Even then, according to Hamer, the virus won’t vanish. “It will probably never completely disappear,” he said. “It will just be under better control.”

Barouch said there’s no “specific magic number” to achieve herd, or population, immunity. “But the more of the population is vaccinated, the faster we’ll see the pandemic resolve,” he said. “I personally would like to see at least three-quarters of the population with immunity.”

That’s a lofty goal, but achievable, according to Barouch, through vaccine education campaigns, starting now and continuing through 2021.