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Your COVID-19 Vaccine Questions, Answered

Wondering which vaccine is the best one to receive, still on the fence about their safety, curious about what happens after vaccination? Here’s what we know.

Editor’s note: This article was updated from an earlier version originally posted on January 27, 2021.

Dr. Jessica Most acknowledges her own bias when she encourages her patients to get the COVID-19 vaccine. “I’ve been a frontline worker taking care of patients with severe COVID-19 infections since March,” Dr. Most, a pulmonologist at the Jane and Leonard Korman Respiratory Institute – National Jewish Health and Jefferson Health, explains. “I feel really strongly that we need to do everything we can to protect our patients from developing severe COVID-19.”

In order for that to happen, Dr. Most says everyone must feel safe and sure to make their own decision regarding vaccination. Here, she breaks down what exactly mRNA vaccines are and answers common questions about what to expect when you get a vaccine and how it changes our lives moving forward.

Dr. Jessica Most after getting her COVID-19 vaccine

Dr. Jessica Most after getting her COVID-19 vaccine.

What exactly is an mRNA vaccine and how does it work?

My definition of a vaccine is anything that’s going to trigger our immune system to make antibodies and other cells so that we are no longer susceptible to that infection. Both Pfizer and Moderna are mRNA vaccines. These vaccines contain a piece of mRNA, which is basically a message. Our cells also make mRNA and they provide messages to our cells to make proteins. This mRNA is delivered via the vaccines to our cells, where it is taken up into the cytoplasm of the cells, where these proteins are made. When our cells receive this message via vaccine, they make the COVID-19 spike protein.

You’ve probably heard about the COVID-19 spike protein because this is the protein that allows COVID-19 to get into our cells. Once the COVID-19 spike protein is made, it is actually displayed on the outside of our cells. When we have this piece of spike protein on our cells, that activates our emergency response system, and we develop COVID-19 antibodies and memory T cells that then remember this is a foreign invader. If we’re exposed to it again after vaccination, our body is going to promptly kill that virus.

What are the differences between the Pfizer and Moderna vaccines?

The Pfizer BioNTech vaccine was issued an Emergency Use Authorization on December 11, 2020, for individuals 16 years and older. The FDA concluded that based on the totality of evidence that they received from the company, this vaccine may be effective at preventing serious or life-threatening disease from infection. They concluded that the known and potential benefits outweighed potential risks of the vaccine. Furthermore, since there is no available approved alternative product for preventing COVID-19 that it was important for vaccine approval to move forward. Now, this vaccine is approved in two doses and they are administered 21 days apart, intramuscularly in your arm. Trial results showed the vaccine efficacy rate was 95%. That is how likely it was to prevent COVID-19 infection.

The Moderna vaccine had Emergency Use Authorization approved on December 18, 2020. The FDA had a similar conclusion that based on the totality of evidence that this vaccine may be effective in preventing serious or life-threatening disease from COVID-19. And that the known benefits outweighed the potential risks, especially given that there was no other available approved or alternative product for preventing COVID-19. This vaccine is only approved for 18 years of age or older and it is two doses that are 28 days apart as opposed to 21 days apart. The trial found vaccine efficacy rate of 94.1% for all individuals enrolled in the trial.

How new is this vaccine technology? Is it safe?

There have been animal studies for over 30 years studying mRNA vaccines. These vaccines are neither a live virus nor a dead virus. It does not have any potential to cause infection with COVID-19. It’s also not integrated at all into our DNA and has no abilities to do so. In that regard, we do not have to worry about changes to our bodies.

One of the reasons that we’ve been able to get these vaccines so quickly is because before COVID-19 was even in the United States, the virus has already been sequenced. Because of this, researchers were able to develop vaccines before COVID-19 had really even taken hold in the U.S.

What are some common side effects from the vaccines?

The common reactions were very similar in both vaccines. Injection site pain was the most common reaction with fatigue being the second most common reaction. Other reactions include headache, muscle pain, joint pains, and chills. Somewhat unique to these vaccines was some lymph node swelling, especially in the armpits, and that all seemed to resolve on their own. There was a low incidence of allergic reactions in both of these vaccine trials.

Can taking ibuprofen or acetaminophen compromise the vaccine? When is it safe to take either if you develop any headaches or flu-like symptoms after getting vaccinated?

There has been a suggestion that taking NSAIDs (non-steroidal anti-inflammatory drugs) like ibuprofen or acetaminophen may diminish your body’s ability to make antibodies. This evidence is taken from vaccine trials in children. However, while this effect was found in some trials, it was not found in others. The short answer is, “we don’t know.” I would err on the side of only taking these medications if you need them. I personally had a really bad headache with my second vaccine and took some ibuprofen.

Are any of the side effects from vaccination contagious?

None of the side effects from the vaccine are contagious. However, there is an effect called the “nocebo” effect. This means that people are more likely to experience side effects if they are told about side effects beforehand. This was seen in the groups of patients who received the placebo vaccine (salt-water). Some of them still had side effects.

Are there long-term side effects to the vaccine?

We really don’t know. There are no anticipated long-term side effects based on animal data, but we have not followed people post-vaccination long enough to know for absolute certain at this point.

Are there any medications that should be postponed when getting the vaccine?

Interestingly, in the vaccine trials, there were some people who had facial swelling, and the common theme was that those patients had had dermal filling agents before they had gotten the vaccination. You should consider postponing those treatments if you’re going to get the vaccine. If you are taking a medication that may affect your immune system like chemotherapy, you should talk with your doctor about the timing of your vaccine.

How strong is the vaccine?

When developing a vaccine, multiple doses are tested. What they do is they use the lowest effective dose, meaning if you had two doses that gave you the same amount of antibodies, they’ll use the lower dose. The short answer is strong enough. The goals of those trials was to make sure that you had significant antibodies to COVID-19 at 28 days.

How long will the immunity to COVID-19 last?

We do not know how long the vaccine will last. The hope is that these vaccines will last quite some time. Physicians are continuing to observe the patients who have already participated in the trials so this information and data collection is ongoing. The answer to this question is a moving target especially with the development of new virus mutations.

How effective are the vaccines to the new strains of the COVID-19 virus?

Both companies have issued statements that the vaccines are effective against the UK mutation. However, there are growing concerns about other mutations being identified, especially in South Africa and Brazil. Moderna is currently developing a booster vaccine to combat these variants.

Those patients who have conditions, or what we’ve referred to as comorbidities, such as lung disease or diabetes, I would say run, don’t walk, to get a vaccine.
—Dr. Jessica Most

Who should get the COVID-19 vaccine?

Everyone. That is currently the recommendation of the CDC and the FDA. Jefferson Health has already vaccinated thousands of healthcare workers, and I am one of them. To date, we do not know of any specific contraindications to getting the COVID vaccines, but let’s talk a little bit about who should have strong consideration. Those patients who have conditions, or what we’ve referred to as comorbidities, such as lung disease or diabetes, I would say run, don’t walk, to get a vaccine.

What about people with allergies?

Currently, the recommendation is that people with allergies can get the vaccine. Since the vaccines have been available in the U.S. there have been some cases of severe allergic reactions. Most of these individuals had a history of anaphylaxis or other allergies. If you have an allergy to PEG or polysorbate (ingredients in the vaccine), you should speak to your allergist before getting vaccinated.

What about immunocompromised individuals?

I’m going to speak specifically here about people getting chemotherapy, people who no longer have a spleen, people on high doses of oral corticosteroids, or people receiving certain immune-suppressing medication for either an autoimmune disease, or other type of problem. Based on other vaccine trials, we have seen that people with these conditions do not mount a robust enough immune response to vaccines. It’s not they’re going to have a side effect to the COVID-19 vaccine, it’s just a question of how well it’s going to work.

My recommendation is that you should speak to your provider about timing. There may be some things that we can do with your medications to make sure that when you get the vaccine, you get the best antibody response possible. Dr. Fauci said, some immunity is better than no immunity. I agree with him. Even if you don’t get as robust an antibody response as someone who is not immunocompromised, it’s certainly worth getting the vaccine because we do know that some immunocompromised individuals are going to have a higher risk of developing severe COVID-19.

What about autoimmune diseases?

I’ll refer back to my answer on immunocompromised patients because many people with autoimmune diseases are on medications that can compromise their immune system. It’s important to talk with your provider about your timing. There has been some concern that the vaccines in general may flare your autoimmune disease. This is a theoretical risk. They did not include anybody that was immunocompromised or with autoimmune disease in any of the vaccine trials so there is still information that we don’t know. I would say the more that people get vaccinated, the more we’re going to learn. I would also say that there are many healthcare workers out there who are either immunocompromised or have autoimmune diseases, and we’re going to be learning from every person who gets vaccinated.

What about pregnant and breastfeeding women?

There were six patients in the vaccine trial that got pregnant during the study and they’re being observed. We do know that animal data suggests that vaccination is not associated with any birth defects. We do not know if there are any long-term risks, and there will continue to be a pregnancy vaccination registry to continue collecting data. Pregnancy is a risk factor for developing more severe COVID-19 infections, and some of the more severe COVID-19 infections that I personally observed early in the pandemic were in pregnant women. Another really important thing to know is that there was no evidence that these vaccines cause infertility. This seems to be a common myth that’s going around social media.

On January 27, the World Health Organization (WHO) advised pregnant women not to take the Moderna vaccine unless they are a health care worker, have preexisting conditions, or in a life or death situation. Is the Moderna vaccine unsafe for pregnant women?

Scientifically, both Pfizer and Moderna are safe for pregnant women to take—at any point in their pregnancy and while breastfeeding. Thousands of women in the U.S. have been vaccinated safely with these vaccines. What WHO stated is that we now have data to support that Pfizer is safe for pregnancy. There is less or limited data on the Moderna vaccine. However, these are very similar mRNA vaccines that are safe. In fact, shortly after WHO made their statement, the American College of Obstetricians and Gynecologists (ACOG) and the Society of Maternal-Fetal Medicine (SMFM) released their own statement, clarifying that no pregnant person should be withheld vaccination.

It would be much worse for pregnant women to get COVID-19 for a number of reasons, including that they are at a higher risk to develop severe COVID-19, for requiring ICU treatment and an increased risk of death.

A pregnant woman’s main priority is the health of their baby. The best way to keep both mom and baby healthy is to be vaccinated. I will also add that both the Pfizer and Moderna vaccines are safe for people trying to conceive. They are also safe for women undergoing fertility treatments. [Editor’s Note: This answer is contributed by Dr. Vincenzo Berghella, director of the division of Maternal-Fetal Medicine at Thomas Jefferson University Hospital.]

Is there anyone who should not get the vaccine?

If you have a severe allergy to any of the components in the vaccine, you should not get vaccinated without discussing it with your allergist. Some people who have severely compromised immune systems have been told by their providers that there are certain vaccines they should not get—those are usually live-virus vaccines. This is not a live virus so it would not fall into that category. It is not recommended to get any vaccine if you have moderate to severe acute illness. If you are acutely ill, like a fever or a cough, it is recommended that you wait a couple of days until you are feeling better before getting vaccinated. The reasoning here is that your body is already fighting an infection and you may not get as robust of an immune response. Your immune response is the key to your ongoing immunity from COVID-19. Plus, we don’t usually like to vaccinate people when they’re ill because it’s very difficult to determine if they have side effects later from the vaccine.

Which vaccine should I get?

The one that is available. You should not wait to get this company’s vaccine or that company’s vaccine. There is no guarantee that there’s going to be a vaccine available if you wait. Currently the two vaccines that are approved have almost identical data. I would anticipate that, even as other vaccines come out, the recommendation will remain that you get the one that’s available.

What happens when I get a vaccinated? What if I have a reaction?

You will remain at your vaccination site for observation right after you’re vaccinated. After that, any reactions should be reported to the provider. Every vaccine reaction is required to be reported through a nationwide reporting system. That has always been the case with every vaccine that has ever been administered. This data is available publicly through the Vaccine Event Reporting System.

Will I have to wear a mask once I get a vaccine?

Absolutely. We see that these vaccines are effective, but they’re effective in environments where we’re still doing things such as masking and social distancing, and we anticipate that mask wearing is going to continue for some time. Until a level of herd immunity is reached and the case rate goes down, it will be important to continue to mask up and socially distance yourself.

If I am vaccinated, can I spread COVID-19 to others?

There is a possibility that even though you don’t get sick from COVID-19, you could potentially spread it to others. It is possible up to 40% of spread is via asymptomatic people. We do know that most other vaccines prevent community transmission. However, we do not know if this is the case with these particular vaccines. We’re hopeful that it is.

What if I only get one dose?

We know that one dose was partially effective, but the recommendation is that really in order to get maximum efficacy, one must get two doses. Remember, don’t wait, vaccinate.

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COVID-19, From the Experts