10 Facts About the COVID-19 Vaccines

Our experts address common questions about the COVID-19 vaccines and explain why they are safe.

COVID-19 vaccine facts

The COVID-19 vaccines are helping us return to normal — but, understandably, many people still have questions. To help answer these questions, NewYork-Presbyterian experts address common concerns about the Moderna, Pfizer-BioNTech, and Johnson & Johnson COVID-19 vaccines.

Question 1: Can these vaccines give you COVID-19?

“It’s impossible for the vaccines to give you COVID-19,” says Dr. Kristen Marks, an infectious disease specialist at NewYork-Presbyterian/Weill Cornell Medical Center. The vaccines use different strategies to deliver just one harmless protein from the SARS-CoV-2 virus to our immune system, she says. “It’s a common misconception and fear, but there is no possible way to contract COVID from the vaccine.”

Since the vaccine teaches our immune systems how to recognize and fight the virus, it can cause symptoms such as fever and body aches. These symptoms are normal and a sign that the body is building protection against the virus.

Question 2: The vaccine was developed so quickly. Is it safe?

“The data that’s been released and reviewed by the FDA shows that these vaccines are very safe,” says Dr. Marks, who is also an associate professor of medicine in the Division of Infectious Diseases at Weill Cornell Medicine.

While the vaccines were created in less than a year, the technologies that made them possible have been in development for years.

“This achievement was possible because scientists leveraged what they learned from past outbreaks of similar coronaviruses and studies, and production of the vaccine was pursued simultaneously with clinical trials, rather than waiting for their completion,” Dr. Marks says.

She adds that none of the usual steps were skipped during the process; the clinical trials have been thorough and extensive, with thousands of participants, for the FDA to evaluate the vaccine’s safety and effectiveness.

Question 3: Can pregnant women get the vaccine?

Individuals who are pregnant may choose to be vaccinated, according to the CDC. The American College of Obstetricians and Gynecologists recommends that the COVID-19 vaccine not be withheld from those who are pregnant. “Based on how the vaccine works, we don’t think there’s any biologic reason that we should be concerned about its safety in pregnancy,” says Dr. Laura Riley, obstetrician and gynecologist-in-chief at NewYork-Presbyterian/Weill Cornell Medical Center.

“We do have lots of epidemiologic data which suggests that pregnancy plus COVID-19 is not a good mix. Pregnant women have had more admissions to the ICU, more mechanical ventilation, and more deaths, although the absolute number is low,” says Dr. Riley, who is also chair of the Department of Obstetrics and Gynecology at Weill Cornell Medicine.

While a doctor’s permission is not required to get the vaccine, talking to a healthcare professional may help guide women in making the decision. “I would suggest you talk to your OB or your midwife,” Dr. Riley says.

Question 4: Can the vaccine cause infertility?

“There is no evidence that the Pfizer, Moderna, or Johnson & Johnson vaccines cause infertility,” says Dr. Zev Williams, chief of the Division of Reproductive Endocrinology and Infertility at NewYork-Presbyterian/Columbia University Irving Medical Center.

“When it comes to infertility, there are typically no obvious symptoms, so it’s understandable that people are fearful that something they are doing — taking certain medications, living in certain environments, or engaging in certain behaviors — could affect fertility,” explains Dr. Williams. “But in the clinical trials and subsequent follow-up, and now with more than 150 million people in the United States already fully vaccinated, we have seen no evidence of a link between the vaccine and infertility.”

Furthermore, the underlying basis for the fear — that antibodies generated by the vaccine could attack the placenta or impact its development — is unfounded, according to Dr. Williams.

“The preponderance of evidence suggests that potential risks associated with vaccination are low, but the risk of complications from COVID-19 during pregnancy is high. We recommend that women who are planning to undergo fertility treatment get vaccinated,” says Dr. Williams.

Question 5: Can people with allergies get the vaccine?

“The vast majority of people with a history of allergies can receive this vaccine safely,” says Dr. Jordan Scott Orange, an allergist-immunologist who is physician-in-chief at NewYork-Presbyterian Morgan Stanley Children’s Hospital. People who have severe allergies not related to vaccines or injectable medicines — such as nuts and other foods, pets, bee stings, latex, or oral medications — can get the vaccine.

The Pfizer and Moderna COVID-19 vaccines are called mRNA vaccines and require two doses. The  CDC recommends that people who have had a severe allergic reaction, specifically anaphylaxis, or an “immediate allergic reaction” (such as hives, swelling or wheezing within four hours) to an ingredient in one of those two vaccines should not get either one. Check with your allergist if unsure. Also, anyone who has a severe or immediate allergic reaction to the first Pfizer or Moderna shot should not get a second dose of either mRNA vaccine.

Consult with an allergist beforehand if you’ve had an allergic reaction to another vaccine or to injectable medicine, says Dr. Orange, who is also chair of pediatrics at Columbia University Vagelos College of Physicians and Surgeons.

Question 6: I have medical problems and take medications. Can I safely get the vaccine?

There’s a reason that the CDC had recommended that people with certain underlying medical conditions be among the first priority groups to get vaccinated. People with a number of health conditions — including Type 2 diabetes, obesity, chronic kidney disease, and sickle cell disease — are at an increased risk of severe illness from COVID-19, according to the CDC.

Dr. Susana Morales, a primary care physician at NewYork-Presbyterian/Weill Cornell Medical Center, notes that the trials testing the vaccines have intentionally included large numbers of people with diabetes, hypertension, obesity, and other health conditions. “A lot of the problems that many of my patients have are problems that the volunteers for the vaccine trials also had, and that was done on purpose,” says Dr. Morales, who is also an associate professor of clinical medicine at Weill Cornell Medicine. “They wanted to have a big cross section of the population.”

People with weakened immune systems and HIV may get the vaccine but should be aware of limited safety and efficacy data, the CDC says.

Question 7: Can the vaccine change my DNA?

“The vaccines do not change or interact with your DNA in any way,” says Dr. Yoko Furuya, chief epidemiologist and medical director of Infection Prevention & Control at NewYork-Presbyterian Hospital and associate professor of medicine in the Division of Infectious Diseases at Columbia University Vagelos College of Physicians and Surgeons.

The Johnson & Johnson vaccine is called a viral vector vaccine, which uses an inactivated (harmless) version of a different virus to deliver important instructions to cells. The Pfizer and Moderna vaccines are called messenger RNA, or mRNA, vaccines. They teach cells how to make a piece of protein that triggers an immune response inside your body. The mRNA from a COVID-19 vaccine never enters the nucleus of our cells, where our DNA is kept. This means the mRNA cannot affect or interact with our DNA. Also, adds Dr. Furuya, “The mRNA degrades quickly and is gone from your body within a few days.”

Question 8: Should I get the vaccine if I have had COVID-19?

“Even if you have already had COVID-19, you should get the vaccine,” says Dr. Furuya.

Experts do not know how long someone is protected from getting sick again after recovering from COVID-19. The immunity someone gets from having an infection, called natural immunity, varies from person to person, and some early evidence suggests that natural immunity after getting COVID-19 may not last very long.  Natural immunity also may not be as protective as a vaccine against some of the circulating variants of concern.

“Because of the severe health effects people with COVID-19 can experience, and because reinfection with COVID-19 is possible, those who had it should get vaccinated,” says Dr. Furuya.

Question 9: Once I’m fully vaccinated, do I need to keep wearing a mask and social distancing?

“For fully vaccinated people, the CDC is saying that you can resume most activities that you enjoyed prior to the pandemic without wearing a mask or social distancing,” explains Dr. Ashwin Vasan, an assistant attending physician in the Department of Medicine at NewYork-Presbyterian/Columbia University Irving Medical Center. “Exercising outdoors or going to the gym, picnicking with your friends, attending small indoor gatherings, eating indoors at a restaurant, or going to see a movie, if you are fully vaccinated, you should be able to do these activities safely without a mask.”

Fully vaccinated people (meaning two weeks have passed since their second dose of the Moderna or Pfizer vaccine or the one dose of the Johnson & Johnson vaccine) can now enjoy a majority of indoor and outdoor activities without a mask, except where required by local, state, or federal law. Masks are still required on public transportation, in nursing homes, correctional facilities, homeless shelters, and schools. And people still need to follow the guidance of workplaces or local businesses if they require masks.

“I think this was the CDC’s way of also giving another incentive to people to get vaccinated, that if you get vaccinated you can start safely doing things without a mask,” says Dr, Vasan. “If we can keep pushing through with vaccinations, we can actually get to where we want to be as a city and as a country.”

Question 10: If a large segment of the population has already been vaccinated, why do I need to get the vaccine?

Herd immunity is the concept that if enough of the population is vaccinated against an infectious disease that it will stop the transmission of that disease. However, “We don’t know how many people need to be vaccinated to achieve herd immunity for COVID-19,” says Dr. Roy M. Gulick, chief of the Division of Infectious Diseases at NewYork-Presbyterian/Weill Cornell Medical Center and professor of medicine at Weill Cornell Medicine. “Some have suggested 70%, 80%, or even 90% or higher.”

Vaccines have proven to be effective against the more transmissible variants that are still circulating. Plus, while the vaccine works very well for most people, some members of the community, such as those whose immune systems are compromised by medication or disease, may not have a strong response to the vaccine, and others cannot take it due to allergies or other medical reasons. So it’s important that “everyone who can get vaccinated get vaccinated so that we can protect ourselves, our families and friends, and all of our community members,” says Dr. Gulick.

Note: Following CDC, FDA and New York State guidance, NewYork-Presbyterian has resumed the use of the Johnson & Johnson COVID-19 vaccine, in addition to continuing to offer the Pfizer and Moderna vaccines. 

If you received the J&J vaccine and develop severe headache, abdominal pain, leg pain, or shortness of breath, please contact your health care provider.

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