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Questions and answers on the COVID-19 vaccine

If you haven’t been vaccinated against COVID-19 yet, why now is the time.

David Da Silva receives a COVID-19 vaccination at the Hynes Convention Center in Boston on June 22.Craig F. Walker/Globe Staff

Over the last months, we in Massachusetts have been fortunate to begin to return to many experiences of normalcy. People fully vaccinated against COVID-19 no longer need to wear masks outside, many beloved local restaurants and businesses have reopened, and we are gathering together more and more to reconnect with friends and family. These experiences have been made possible by the protective power of vaccination and our continued public health measures.

We write now because it is important to recognize that COVID-19 hasn’t disappeared and there continue to be lives lost due to this virus. The more transmissible Delta variant has become the most common cause of new infections in the United States, and infections continue to occur across the country, with recent increases being seen in areas with a lower vaccination rate. It is important to know that those who have not yet been vaccinated remain susceptible. Dr. Rochelle Walensky, director of the Centers for Disease Control and Prevention, recently estimated that 99.5 percent of COVID-19-related deaths in the United States in the past six months occurred in unvaccinated people.


As infectious diseases physicians, we have received questions from patients who are hesitant to get the vaccine. Here, we outline the most common questions and our answers. Our responses are derived from scientific evidence, public health data, and our collective expertise. Our goal is to inform you, to promote fact-based decision making, and, yes, to help you join the 600 million people in the world who have opted to receive the COVID-19 vaccine.

How do I know it’s safe?

The safety of the three vaccines currently authorized by the Food and Drug Administration for use in the United States was initially established through rigorous clinical trials involving tens of thousands of participants, FDA review, and external scientific review. There is now real-world data on safety from over 100 million people who have received at least one dose of vaccine in this country.


First, it is important to emphasize that it is not possible for the vaccine to give you a COVID-19 infection, because it does not contain the virus. Likewise, people do not shed any COVID-19 virus after getting the vaccine and they pose no risk to others.

In terms of overall safety, the results are reassuring, and initial studies anticipated almost all of the vaccine reactions. Common side effects include soreness at the site of the injection as well as flu-like symptoms, including fatigue, headache, body aches, chills, or fever. Side effects are mild to moderate in most people who experience them and last only a day or two. Severe allergic reactions are extremely rare, but talk with your physician if you have a history of severe allergy to any component of the vaccine — they can recommend which vaccine(s) you can safely receive based on your health history.

The identification of serious medical events in patients receiving the Moderna and Pfizer vaccines (myocarditis) and the Johnson & Johnson (J&J) vaccine (blood clots and Guillain-Barré syndrome) underscore the level of scrutiny and vigilance devoted to the vaccination program. These events are exceedingly rare, estimated at three to four per million for blood clots and 16 per million for myocarditis, less than the odds of getting struck by lightning in a person’s lifetime and far less than the risk of COVID infection or the lingering side effects of COVID-19 after being infected. The possible rare association of Guillain-Barré syndrome with the J&J vaccine will continue to undergo review. These events each warrant attention and possibly a discussion with your doctor, but the vast majority of people can be vaccinated safely.


Some of our patients raise concern over the novel platform used for the COVID-19 vaccines (mRNA and recombinant adenovirus vaccines) and the speed with which they were developed. It is important to know that mRNA vaccines have been studied in people for more than 15 years, beginning in 2006. The J&J vaccine uses the same recombinant adenovirus technology used in a vaccine approved by the FDA in 2019 to prevent Ebola virus infection.

How do I know the mRNA vaccine will not enter my brain or my DNA?

The mRNA vaccines do not get into the brain and do not change or alter your DNA. The mRNA in the vaccine prompts your cells to make a viral protein (the spike protein) that generates an immune response against the virus. The mRNA is then degraded by your cells within a day or two without ever entering the cell nucleus, where your genes reside. This response to the spike protein allows your immune system to recognize the COVD-19 virus if you come in contact with it in the future and prevents you from getting sick.

Infection with COVID-19, on the other hand, can result in neurological symptoms. A recent study of over 200,000 patients found that one-third of COVID-19 survivors had a new neurological or psychiatric diagnoses six months after infection. The best way to prevent these complications is to avoid getting COVID-19 infection. Get vaccinated instead.


Will the vaccine cause infertility or miscarriages?

There is no evidence to suggest that COVID-19 vaccines cause infertility or miscarriages. Mounting data from tens of thousands of pregnancies support the safety of these vaccines in pregnancy.

The vaccines do not cause infertility. Internet postings raising concern over infertility related to the spike protein are false. Neither COVID-19 infection, the spike protein, nor antibodies to the spike protein induced by vaccination have been linked to infertility. Thus, there is no scientific evidence to support a concern for infertility related to the COVID-19 vaccine.

Pregnant women who contracted COVID-19 infection while pregnant have not had an increase in miscarriage rates. The antibodies to spike protein generated during natural infection are the same as those developed in response to vaccine — and these have not had the result of affecting fertility. It is important to remember that compared with nonpregnant women, pregnant women infected with COVID-19 are more likely to be hospitalized and have severe illness.

I already had COVID and recovered. Why should I get vaccinated?

Although COVID-19 infection does result in natural immunity to the specific strain for up to 90 days, the immunity will decrease over time and leave you susceptible to another COVID infection. It also will not protect you against all variants. Vaccine will provide longer durations of immunity in most people and also be effective against currently circulating variants.


Does the vaccine work against the new Delta variant, and will I need another dose?

The currently available data suggest that all three emergency-use authorized vaccines are expected to have strong protection against the currently circulating variants in the United States, such as the Delta variant, in particular against severe infection causing hospitalization or death. While there are rigorous ongoing studies reviewing when or if a booster dose might be required, this is not currently recommended by the FDA or CDC.

If you have not yet been vaccinated, you have valid questions and concerns, and we recognize that vaccination can be a very personal and emotional decision for many people. We want to do our part to help keep you healthy and safe and share with you that the overwhelming evidence favors vaccination as a means to protect you from COVID-19 infection and put an end to this pandemic. The best thing you can do is to take care of your medical and mental health conditions, and also get vaccinated against COVID-19 infection. COVID-19 vaccination can protect you, and it can protect the people you love. Vaccination is supported by scientists, public health experts, politicians on both sides of the aisle, religious leaders, and us, your infectious diseases doctors.

More questions? Click here Key Things to Know About COVID-19 Vaccines (

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Dr. Tamar Foster Barlam is chief of the Section of Infectious Diseases at Boston Medical Center. Dr. Helen W. Boucher is dean and interim chief academic officer chief at Wellforce Health System/Tufts Medical Center. Dr. Kalpana Gupta is associate chief of staff and chair of the Infectious Diseases COVID-19 Response Team of Veterans Affairs at Boston Healthcare System. Dr. Daniel R. Kuritzkes is chief of the Division of Infectious Diseases at Brigham and Women’s Hospital. Dr. Mary LaSalvia is interim chief of the Division of Infectious Diseases at Beth Israel Deaconess Medical Center. Dr. Matthew R. Leibowitz is chief of Infectious Diseases at Newton-Wellesley Hospital. Dr. Katherine McGowan is chief of Infectious Diseases at Brigham and Women’s Faulkner Hospital. Dr. Louise Ivers is interim chief of the Division of Infectious Diseases at Massachusetts General Hospital. Dr. Kenneth M. Wener is chair of the Division of Infectious Diseases at Lahey Hospital and Medical Center.