COVID-19 Vaccine Safety and Effectiveness: Updated Information

An MSK employee after receiving a COVID-19 vaccine

Large studies have found that the COVID-19 vaccines are highly effective and safe.

On August 23, Memorial Sloan Kettering Cancer Center doctors, nurses, and staff welcomed news that the Pfizer-BioNTech COVID-19 vaccine (Comirnaty®) received full approval from the Food and Drug Administration (FDA). The federal agency issued its decision after a thorough review of Pfizer-BioNTech’s updated clinical trial and manufacturing data. It was previously was administered under an Emergency Use Authorization.

The FDA’s approval is a significant milestone in the long battle against this devastating virus, which has claimed more than 625,000 lives nationwide. The pandemic has intensified again in recent weeks, fueled in part by the highly transmissible Delta variant. The evidence is clear: Vaccination remains our most effective weapon against this tenacious virus and our best opportunity to end this pandemic.

Mini Kamboj, MSK’s Chief Epidemiologist, answers some frequently asked questions about the COVID-19 vaccines and how they work.

How effective are the COVID-19 vaccines?

All three COVID-19 vaccines provide strong protection against severe disease, hospitalization, and death from COVID-19.

The FDA approved the Pfizer-BioNTech COVID-19 vaccine based on updated clinical trial and manufacturing data, which show the vaccine is 91% effective in preventing infection, hospitalization, and death from COVID-19.

The Moderna vaccine has been shown to be 94% effective and the Johnson & Johnson/Janssen vaccine has been shown to be 66% effective.

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How does the effectiveness compare with vaccines for other diseases?

The COVID-19 vaccines are among the most effective vaccines in history. They are as effective — if not more — than vaccines for polio, chicken pox, measles, and the flu.

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How do the COVID-19 vaccines work?

The Johnson & Johnson/Janssen vaccine, the Pfizer-BioNTech vaccine, and the Moderna vaccine all work by teaching cells how to make one part of the COVID-19 virus (the spike protein) in order to trigger an immune response. What those instructions look like and how they make their way inside your body is a little bit different depending on which vaccine you get.

In all cases, the vaccine trains your body to recognize the virus so that if you are infected, your immune system is ready to fight it.

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How can I be assured the COVID-19 vaccines are safe?

Public health authorities are closely watching for any signs of potential safety problems. A few extremely rare instances of severe side effects have emerged and been investigated, but scientists have concluded the risk of getting severely ill from COVID-19 is far greater than the risk of these side effects. Here is proof of this careful and ongoing scrutiny:

  • In mid-July 2021, the CDC said that about 100 out of 13 million Americans who received the J & J vaccination developed Guillain-Barré syndrome. Guillain-Barré syndrome is a rare neurological condition in which the body’s immune system attacks nerve cells. Read more here »
  • In late June 2021, the CDC reported that more than 1,200 Americans experienced heart inflammation potentially linked to the Pfizer-BioNTech and Moderna vaccines. The heart issues were very rare — overall, for every million second vaccine doses administered, there were 12.6 cases of heart inflammation. Read more here »
  • In the spring of 2021, an advisory panel to the CDC launched an investigation after reports of a handful of cases of a highly unusual but severe blood clotting disorder in people who had received the J & J vaccine. This disorder, called cerebral vein sinus thrombosis with thrombocytopenia, is characterized by blood clots in the brain and other organs and low platelet counts. The investigation found, as of April 21, 2021, a total of 15 cases of this disorder, including three deaths, out of 8 million Americans who’d received the J & J vaccine. Read more here »

You should also know there is incorrect information from unreliable sources on social media about how the Pfizer-BioNTech and Moderna vaccines use something called Messenger RNA (mRNA). The facts are that there are thousands of different kinds of mRNA in human cells. Each kind of mRNA does different things.

It’s important to know mRNA is not the same as DNA and cannot be combined with DNA to change your genetic code.

Here’s how the mRNA vaccines work: They use a tiny piece of the coronavirus’ genetic code to teach your immune system how to make a protein that will trigger an immune response if you get infected. The mRNA is fragile, so after it delivers the instructions to your cells, it breaks down and disappears from the body (in about 72 hours). The mRNA never even goes into the nucleus of the cell — the part that contains your DNA.

The vaccines do not cause cancer. They do not expose you to the virus that causes COVID-19. You cannot get COVID-19 or any other infection from the vaccine. Read more about how mRNA vaccines work here »

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Do the COVID-19 vaccines contain animal products?

No, the Pfizer-BioNTech, Moderna, and Johnson & Johnson vaccines do not contain animal products or animal-derived ingredients such as pork, shark squalene, gelatin, cholesterol, egg, or milk. In addition, none of them contain preservatives, gelatin or latex. All COVID-19 vaccines also are free from metals such as iron, nickel, cobalt, lithium, rare earth alloys or any manufactured products such as microelectronics, electrodes, carbon nanotubes, or nanowire semiconductors.

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The COVID-19 vaccines were developed so quickly. How can I be sure researchers did not skip important steps?

The COVID-19 vaccines were developed fast because scientists had a head start. The technology already existed and using it to develop a vaccine for a new virus became an international priority, unlocking billions of dollars to ensure safety while moving urgently to save lives. Regulators streamlined some steps in the authorization process, but the vaccines still had to meet the FDA’s rigorous safety and effectiveness standards.

The CDC is carefully tracking all adverse reactions, and they have been rare.

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What are the side effects of each vaccine?

The vaccines reported similar side effects, which don’t last long — about one to three days. People receiving the vaccines reported pain at the injection site, fatigue, headache, and muscle pain. Severe adverse reactions are rare. For the Pfizer-BioNTech and Moderna vaccines, side effects were more common after the second dose.

People with common allergies to medications, foods, inhalants, insects, and latex are no more likely than the general public to have an allergic reaction to the mRNA vaccines, according to guidance from the American College of Allergy, Asthma, and Immunology.

The Second Dose of a COVID-19 Vaccine: Side Effects, Why They Happen, and How to Treat Them
Learn about the Pfizer-BioNTech and Moderna vaccines, which both require two shots.
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Can I do anything ahead of time to reduce any side effects from the vaccine?

It’s important that you do not take over-the-counter drugs before getting your vaccine because there are concerns that some pain-relieving drugs may interfere with the immune response to the vaccine. It is also unclear if taking medication ahead of time actually works to reduce post-vaccine symptoms. You should wait until after being vaccinated to see how you feel. If you do experience side effects, it is OK to take an over-the-counter drug like Advil or Tylenol to lower a fever, reduce chills, or relieve a headache or body aches.

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What if I experience swelling or tenderness away from where I was injected?

Some people may experience some swelling or tenderness in their lymph nodes. It is also possible that this swelling will show up on imaging tests and could be mistaken for progression of certain cancers — primarily breast, head and neck, melanoma, and lymphoma.

This vaccine side effect usually occurs within two to four days after the vaccination and can last for an average of ten days.

On imaging tests, the lymph node enlargement may be detected for a longer period. For these reasons, we recommend:

  • If you develop this symptom after you’re vaccinated, you should speak to your doctor. Most of the time, they will recommend that you wait at least four weeks before getting further tests to give time for the swelling to disappear.
  • You should schedule your COVID-19 vaccination after any routine imaging. If you’ve already had the vaccine, we recommend you wait six weeks for any routine breast screenings, including mammography and breast MRI.
  • If you’ve had cancer, you should ask for your COVID-19 vaccine to be administered on the opposite side of your cancer diagnosis if possible.
  • If you have any discomfort from the swelling, you can use a warm compress. Acetaminophen or nonsteroidal anti-inflammatory drugs may be taken to ease the discomfort.

It’s important to know that all kinds of vaccines can cause temporary swelling of the lymph nodes, which may be a sign that the body is making antibodies in response as intended.

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How do we know the vaccines will work well in all groups?

All three drug makers conducted rigorous studies that included people across a range of ages, gender, racial, and ethnic groups.

In the Pfizer-BioNTech study, 42% of people were over the age of 55, and 20% had other medical conditions. Minority and ethnic groups represented 17% of vaccine volunteers.

In the Moderna study, about 25% of the people in the study were over age 65. The study group was 63% white, 20% Hispanic/Latinx, 10% Black/African American, 4% Asian, 1% Native American, and less than 2% other.

In the Johnson & Johnson study, 59% of people were white; 45% were Hispanic/Latinx; 19% were Black/African American; and 9% were Native American. Overall, 34% of participants were over age 60.

All three vaccines offered strong protection against COVID-19 in all these groups.

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Will the COVID-19 vaccines protect against variants?

Preliminary research indicates that the vaccines are effective against emerging COVID-19 variants.

Because the vaccines are extremely effective, they could still offer substantial protection, even if they don’t work as well against a new variant.

The emerging variants are another reason why you should get vaccinated against COVID-19 as soon as you are eligible. The faster people are vaccinated, the less chance the virus will have to develop a new mutation. Read more here »

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Should people with cancer get the COVID-19 vaccines?

We recommend our patients with cancer get the COVID-19 vaccine. Some cancer treatments like chemotherapy or radiation can reduce how well a person’s immune system responds. It’s possible that the COVID-19 vaccines may not be as effective in those patients. Even so, some protection is better than none.

Why Cancer Patients Should Be Vaccinated against COVID-19 and What Is Safe Afterwards
Learn what every person with cancer should know about the COVID-19 vaccines.
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What about cancer patients with severely weakened immune systems?

We believe the COVID-19 vaccines will be safe for patients with severely weakened immune systems, for example, as the result of a stem cell transplant. But these vaccines may not work as well during certain phases of cancer treatment. You should discuss the timing of getting a COVID-19 vaccine, as well as the risks and benefits, with your MSK care team.

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Are COVID-19 vaccines safe for women who are trying to get pregnant, are pregnant, or breastfeeding?

We recommend the COVID-19 vaccine to people who are pregnant, breastfeeding, or trying to get pregnant.

Currently, there is no evidence that COVID-19 vaccines cause any problems with pregnancy, including development of the placenta. More than 60,000 pregnant women who have been vaccinated are registered with the CDC. A group of them are being closely monitored to see how the vaccine affects pregnant people. No safety concerns have emerged.

New research shows pregnant women who are vaccinated not only protect themselves but also their babies. Pregnant women who received the Pfizer-BioNTech and Moderna vaccines had COVID-19 antibodies in their umbilical cord blood and breast milk, according to the Journal of Obstetrics and Gynecology. While these studies are preliminary, they offer encouraging evidence that some of a mother’s immunity can be passed along to the baby before and after they are born.

There is no evidence that the COVID-19 vaccines cause infertility in women or men.

Pregnant People Should Be Vaccinated: Latest Information on COVID-19 Vaccine Safety
Deborah Goldfrank, Head of General Gynecology at MSK, explains what we know about the safety of COVID-19 vaccines for pregnant and breastfeeding mothers and their babies.
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Are the vaccines safe for me if I have already had COVID-19?

The CDC encourages people who have had COVID-19 to get vaccinated. Some of the people in the vaccine studies had evidence of a prior COVID-19 infection. They had side effects from the vaccine that were similar to those who had not been previously infected.

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Should I get an antibody test after the COVID-19 vaccine to make sure it’s working?

Antibody testing is not currently recommended to check someone’s immunity to COVID-19 following vaccination. The COVID-19 antibody test used at MSK detects the immune response after being infected by COVID-19; it does not measure the immune response as a result of the vaccine. That’s why it should not be routinely ordered to assess vaccine response.

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How long does the vaccine protection last? Will people need to get it annually, like the flu shot?

It is too early to tell how long the vaccines will provide protection against COVID-19 or whether follow-up shots will be needed on a regular basis. No vaccine provides 100% protection against getting the virus or spreading it to others, which is why it’s very important to continue following safety guidelines, such as social distancing, wearing masks, and regularly washing hands. Read about how some people with cancer may need to receive a third dose of the COVID-19 vaccine »

 

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Are MSK employees required to be vaccinated?

Yes. All MSK employees must be vaccinated against COVID-19 as a condition of their employment. MSK is following the New York State and New Jersey COVID-19 vaccine mandates for healthcare workers.


August 25, 2021


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