The COVID-19 vaccine rollout in Massachusetts has lagged far behind other states. The commonwealth received over 1.4 million doses, according to the the Massachusetts Department of Public Health, but just 748,544 residents had received their first dose as of Feb. 11.

While some of the delays in Massachusetts have been due to logistical hurdles and limited supplies, many people are also hesitant about getting the vaccine because they worry about side effects. But the Centers for Disease Control and Prevention says that the vaccines' side effects — like pain or swelling at the injection sight, fever, tiredness, chills or headache — are normal, generally mild and should clear up in a few days. The CDC has information on its website about what to expect after getting a COVID-19 vaccine that outlines in greater detail the possible side effects and when to consult a doctor.

Experts emphasize that these side effects mean the vaccine is working and that they're much less severe than the potentially life threatening symptoms caused by COVID-19.

Four Boston-area doctors spoke with GBH News about what to expect when getting either the Moderna or Pfizer vaccines. Dr. Erica Shenoy works in the Infection Control Unit at Mass General Hospital and teaches at Harvard Medical School. Dr. Roger Shapiro is an infectious disease specialist at Beth Israel Deaconess Medical Center and an associate professor of immunology and infectious diseases at the Harvard T.H. Chan School of Public Health. Dr. Shira Doron is hospital epidemiologist at Tufts Medical Center. Dr. Neil Maniar teaches public health practice at Northeastern University.

Their responses have been edited for length and clarity.

What are the side effects people may experience after receiving the Moderna and Pfizer vaccine?

Shenoy: At the location where the shot is administered, it is very common to have some pain, some swelling, some redness. That is very common. Other common side effects that people might feel would be to be a little bit more tired than usual. They might have a headache; they might have some chills. So, the best thing to do is review the CDC website.

Shapiro: All the vaccines will have some side effects, and those are natural and expected parts of the vaccination process. It's an indication that the vaccine is doing what it should be doing and it's working to stimulate the immune system. The immune system is what gives the side effects. It's your own immune system recognizing the proteins in the vaccine and basically saying, I don't like this and I'm going to react to this. And that's what causes things like a sore arm and fevers, headaches and muscle aches.

Is it OK to take over-the-counter medicines, like ibuprofen, to reduce the sife effects before or after getting vaccinated?

Doron: While we don't recommend taking anything [over-the-counter] before, we certainly don't want people to shy away from taking what they need to take to control symptoms after vaccination. If you have fevers and chills and joint pains and muscle pains, it's totally fine to take Tylenol or ibuprofen over the counter to control those side effects.

Shapiro: Most people are fine riding it out and doing nothing. But if people are feeling that they would like to take ibuprofen or Tylenol, I think it's entirely fine to do that after you receive the vaccine. CDC and others do not recommend taking anything before you get the vaccine, because we really want to have the immune system respond to the vaccine, and we don't want to dampen anything in the immune system. Ibuprofen can potentially do that. Tylenol, much less likely. And so, it's recommended not to do it before you get the vaccine, but [wait until] after you get the vaccine.

Is age a determining factor as to the severity of side effects?

Doran: It has been shown that people who are younger tend to have more prominent side effects. But I've talked to plenty of young people who did just fine. And certainly, I've talked to older people that had significant symptoms. So, it's not a hard and fast rule. Every person is different in terms of how they react, and it's very difficult, if not impossible, to predict how someone is going to react to the vaccine.

Shapiro: There is a little bit of a breakdown in an age when you look at the different vaccines. The Pfizer vaccine was broken down — in the New England Journal of Medicine, they broke it down by greater than [age] 55 and less than [age] 55. And those who are younger than 55 experienced slightly higher rates of fever, fatigue, headache, chills, occasionally, and muscle pains and joint pain. It's just a little bit higher in each category. That's understandable when we think about the more vigorous immune systems of younger people responding to the vaccine challenge. So it's a little bit worse in younger people, but [it] probably shows gradation by age.

Can side effects from the second vaccine be worse than the first?

Doron: In many cases, the second shot is associated with more prominent symptoms. The first one sort of primes the immune system, and then the second one really drives it home. You are now ready to withstand an onslaught of COVID-19 virus. That's the way these vaccines are designed to work, as a two-dose regimen.

Shapiro: In terms of the second shot, it's completely understandable why the second shot may increase the symptoms that people feel after getting vaccinated. Your body's already seen the vaccine one time, and it recognizes that this is a foreign protein that it has already started to respond to. It's been primed, and it's ready to kick into gear the second time to do even more to boost up the immune response. And that's the whole purpose of the second shot.

What if a person has an allergy — can they get vaccinated?

Doran: We are vaccinating people who have allergies. Really, the only people that we don't vaccinate are people who have a known allergy to a component of the vaccine itself, which would be extremely rare. The components of the vaccine are not things that people would have experienced before.

Shapiro: Rarely we might see — very occasionally — more allergic reactions, but those should be distinguished from the more typical side effects. And I should highlight that allergic reactions are really very rare to these vaccines, certainly to the mRNA vaccines, the Pfizer and the Moderna. It only occurred in a handful of patients out of the millions that have received the doses.

If a person develops a rash at the site of the injection, is that cause for concern?

Shenoy: It causes a lot of distress to patients who have had it, but it's not something that should prevent you from getting the second shot. I would definitely take a look at what's been posted in terms of the pictures of this so that, if it happens to you, you can understand it and know what to expect.

What is the best way to mentally prepare if someone is apprehensive about getting the vaccine injection? Should they consult a physician first?

Maniar: The fear of needles is very common. My recommendation is to find some calming techniques. If you tense up, you're going to feel it more than if you're relaxed. It's a relatively, if not totally painless, procedure. It is it is absolutely worth the minor little pinch that you feel getting that shot is absolutely worth the protective effects of this vaccine to keep individuals safe and importantly, to keep people around them safe.

Shapiro: Most people should generally stay on their drugs. And the general recommendation would be to go ahead and get vaccinated and take whatever drugs you need to be on for your own health and then get vaccinated on top of that. But people should check with their physicians if they have concerns about whether they need to and whether it's OK to be on their drugs when they get vaccinated.

What else is there to know about getting the vaccine and benefits to our health?

Maniar: This is the ticket back to normalcy. It's a big step towards having us get back to our pre-COVID way of life. But it's still really important, after individuals get their vaccine, after they get their first dose and even after they get their second dose, that individuals continue to wear masks when they go outside, when they're around others. What we know right now is that the vaccines are highly protective for individuals against severe illness, against people getting sick from coronavirus infection. What we don't know with certainty yet is the extent to which the vaccines limit the transmission of the virus from one person to another.

Doran: You are well protected against hospitalization and death, for sure. But none of the vaccines are 100% effective. There are what we call breakthrough infections. We are still in a period where there is a lot of coronavirus circulating in the community. There is a potential that even with vaccination, you could have asymptomatic infection and transmit it to somebody else. We're certainly not wearing a special hat that says, "I'm vaccinated, therefore I don't have to follow any rules anymore." So, for so many reasons, we should get vaccinated, but it does not quite yet give us the privilege of changing a lot of what we do.