COVID-19: Vaccine Facts

The vaccine protects you from COVID-19. No matter how old you are, COVID-19 can lead to complications and death. Even if you had COVID-19, it is important to get vaccinated because it lowers your risk of getting COVID-19 again and may prevent you from passing it on to others.

Also, getting vaccinated may protect those around you, particularly people who cannot get the vaccine, such as children. Vaccination, along with other prevention measures, can help us end the COVID-19 public health emergency.

Below is information about the vaccines, including how they work, when and where to get vaccinated, and what to expect when you get vaccinated.

Vaccine Development and Authorization

Creation and Testing

The COVID-19 vaccines followed the same development steps as other vaccines: they were developed and tested in a laboratory and then went through clinical trials closely monitored by the U.S. Food and Drug Administration (FDA).

Clinical trials involve testing the vaccine in people to see if it is safe and effective. The COVID-19 vaccines were each tested on tens of thousands of people of different genders, ages, races and ethnicities who volunteered to be part of the clinical trials.

Production Timeline

Development of the COVID-19 vaccines involved an unprecedented amount of resources. Billions of dollars have been spent and hundreds of scientists from around the world have been working nonstop on developing vaccines since the spring of 2020. Scientists built on many years of research from other vaccines, including research on vaccines for other coronaviruses.

The federal government provided special funding to allow development, testing and production of the vaccines to happen at the same time. This allowed companies to start manufacturing vaccines even before they were authorized for use. The federal government, state and local health departments and health care providers have been working for months on plans for storage, distribution, supplies and other logistics. The goal was to deliver and administer the vaccines as soon they were authorized for use.

Emergency Use Authorization

In an emergency, the FDA may allow vaccines (and other treatments) to be used by granting an Emergency Use Authorization (EUA). Both the Pfizer and Moderna vaccines have been granted EUAs.

All vaccines granted an EUA must go through the same clinical trials as all other vaccines. The FDA may grant an EUA only if evidence strongly suggests the benefits of getting the vaccine outweigh any risks to patients.

The FDA also expects manufacturers whose COVID-19 vaccines are authorized under an EUA to continue clinical trials in order to get additional safety and effectiveness information, and to apply for approval (licensure).

Vaccine Safety and Effectiveness

Safety Evidence and Monitoring

The authorized vaccines were shown to be safe through clinical trials. These trials involved testing the vaccine on tens of thousands of volunteers. The process was monitored closely by the FDA and other organizations.

To ensure the safety of the vaccines:

  • The FDA reviewed clinical trial plans and protocols to make sure the procedures met the highest scientific and ethical standards.

  • Clinical trials were closely monitored by data safety monitory boards made up of outside experts (medical personnel, ethicists, statisticians, patient advocates), among other groups.

  • FDA scientists and medical professionals evaluated all available information to determine if the vaccines should be authorized.

  • Several federal agencies and organizations have continued to monitor the safety of the vaccines as they are administered.

Allergic/Adverse Reaction Tracking

Health care providers are required to report certain adverse events following vaccination to a national reporting system, called Vaccine Adverse Event Reporting System (VAERS), managed by the CDC and FDA.

People can also self-report side effects or other reactions to VAERS online or by calling 800-822-7967.

The CDC has also created a smartphone app called V-safe that people can use to report reactions to the vaccine.


Both vaccines are very effective.

In clinical trials, the Pfizer vaccine was shown to be 95% effective and the Moderna vaccine 94% effective at protecting trial participants from COVID-19. This means that at least nine of every 10 people vaccinated during clinical trials were protected from the disease.

Both vaccines were shown to be safe and effective across all gender, age, race and ethnicity groups included in the clinical trials.

Bell's Palsy

Out of the tens of thousands of people who received one of the two vaccines during clinical trials, a few developed Bell’s palsy (facial paralysis). However, the FDA did not determine these cases were caused by the vaccines. The rate of Bell’s palsy seen during the clinical trials was not above the rate expected in the general population.

People who have had Bell’s palsy can be vaccinated. If you have had Bell's palsy and have questions about vaccination, talk to your health care provider.


There have been no reported cases of Guillain-Barré syndrome following vaccination among participants in the Pfizer or Moderna clinical trials. People who have had Guillain-Barré syndrome can be vaccinated.

If you have had Guillain-Barré syndrome and have questions about vaccination, talk to your health care provider.


Infertility has not been found to be a problem in women who have had COVID-19, so it would not be expected to be an issue for the vaccine. People who are trying to become pregnant now or who plan to try in the future can be vaccinated. Vaccines are monitored and tested before being authorized for use and after. There is no evidence fertility problems are a side effect of COVID-19 vaccines, or of any other vaccines.

Claims of infertility are based on a misunderstanding of the science. The COVID-19 vaccines — similar to many other vaccines — work by teaching our body to create antibodies to fight the virus. Concerns of infertility are based on the idea that the antibodies will attack a protein in the placenta that has a few things in common with a protein found in the COVID-19 virus. However, the two proteins are very different, and our immune systems are smart enough to tell the difference. There is currently no evidence these antibodies will cause any problems in pregnancy, including development of the placenta.

Vaccine Cannot Cause COVID-19

Neither the Pfizer nor Moderna vaccine contain the virus that causes COVID-19. It is not possible to get COVID-19 from the vaccines.

Vaccine Ingredients and How They Work

Messenger RNA (mRNA) Vaccines

Both the Pfizer and Moderna Vaccines are messenger RNA (mRNA) vaccines. mRNA is a molecule that contains the blueprint for making proteins. These are the first mRNA vaccines to be authorized, but the technology has been studied for over 30 years.

Here’s how mRNA vaccines work:

  1. The mRNA molecules enter the body with instructions on how to make a protein that is part of the virus that causes COVID-19.

  2. The proteins produced trigger the body to make antibodies (special proteins that fight against a specific infection) and other defenses.

  3. The mRNA is then broken down and destroyed by the body.

  4. If a person is exposed to COVID-19 after they were vaccinated, the body will be able to recognize the virus and produce antibodies and other defenses to fight it.

In short, mRNA is similar to email that gets sent to your body with instructions on how to identify and destroy the virus. Your body uses those instructions and then deletes the email completely.

mRNA does not interact with or change a person's DNA.


In addition to mRNA, the vaccines contain only the following types of ingredients:

  • Lipids: Lipids are molecules of fat that do not dissolve in water. They surround the mRNA, protecting it so it does not break down before it gets into your cells. One example of a lipid included is polyethylene glycol.

  • Salts, acetic acid and amines: These are all used to protect your cells by keeping the pH (acidity level) of the vaccine similar to the pH in your body. The Pfizer vaccine contains four salts, including table salt. The Moderna vaccine contains acetic acid (the kind of acid in vinegar), one salt and two organic compounds derived from ammonia known as amines.

  • Sugar: Sugar helps keep the lipids from sticking to each other or to the sides of the vaccine vial.

The vaccines do not contain:

  • Antibiotics
  • Blood products
  • DNA
  • Fetal tissue
  • Gelatin
  • Gluten
  • Mercury
  • Microchips
  • Pork or other animal products
  • The virus that causes COVID-19

See a full list of ingredients for the Pfizer vaccine (PDF) and the Moderna vaccine (PDF).

How Long the Vaccines Work

We do not yet know how long the vaccines will protect people from COVID-19. It may be that a vaccine is needed annually, similar to a flu shot, or that an additional shot or booster shot is needed, such as with a tetanus shot. It is also possible that no additional vaccine will be needed after the first two doses.

Continued research and time will tell us how long the vaccines’ protection last and whether people may need additional doses. Participants in the clinical trials will continue to be monitored, and we will learn more over time from the millions of people being vaccinated around the world.

Impact on Disease Transmission

The clinical trials showed both the Pfizer and Moderna vaccines are effective at preventing symptoms of COVID-19 and severe illness due to COVID-19.

More research is needed to see whether the vaccines prevent people from getting and spreading the virus.

Herd Immunity

Herd immunity is when enough people in a population have immunity (protection) against a contagious disease that the disease is unlikely to spread. As a result, even people who are not vaccinated are at lower risk for infection. The percent of the population that needs to have immunity to reach herd immunity is different for different diseases.

For COVID-19, experts do not yet know what percentage of people would need to be vaccinated to reach herd immunity. However, even before we reach herd immunity, having a large number of people vaccinated will lower the number of people who get sick and are hospitalized or die from COVID-19.

New Variants/Strains of the Virus

It is normal for a virus to mutate (change) over time and for new variants to occur. Several variants of the virus that causes COVID-19 have been identified. Some of these variants seem to spread more easily and quickly than others, which may lead to more cases of COVID-19.

The vaccines are expected to protect against emerging variants detected to date, though the data are very preliminary. Scientists are working to learn more about these variants and how they affect vaccines.

Vaccination Eligibility

Currently Eligible

COVID-19 vaccines will likely be available for most New Yorkers by mid-2021. Until there is enough supply available, people with an increased risk of getting COVID-19 or of having severe COVID-19 illness are being prioritized for vaccination.

New York State determines what groups are prioritized, and the timeline for distribution for the entire state. Prioritization is based on guidance issued by the CDC Advisory Committee on Immunization Practices.

For a complete list of who is eligible to get a vaccine now, visit COVID-19: Vaccine Eligibility.

Immigration Status Does Not Matter

COVID-19 vaccines are available to people of all immigration statuses. Your immigration status does not matter to us and you will not be asked about it at the vaccination site.

COVID-19 vaccination is not considered a public benefit under the public charge rule. Getting vaccinated will not negatively impact you or your family’s immigration application.

Age Restrictions and Availability for Children

People ages 16 and older can be vaccinated.

People ages 16 and 17 can only get the Pfizer vaccine, as the Moderna vaccine has only been authorized for people ages 18 and older. Vaccination for people ages 16 and 17 requires child assent and parental consent.

Pfizer and Moderna have recently begun studies to see if their vaccines are safe for children. If a vaccine is shown to be safe and effective for children, the FDA can authorize its use for children. The earliest this is likely to occur is mid-to-late 2021.

Medical History and Clinical Considerations


Most allergies are not a concern for COVID-19 vaccination. You can get vaccinated if you have a history of allergic reactions not related to vaccines or injectable medications — such as allergies to food, antibiotics or other medicine that you take by mouth, pet dander, venom, dust mites, pollen, mold, cigarette smoke, or latex — or if you have a family history of allergic reactions.

If you have a history of severe allergic reactions (such as anaphylaxis) to anything, let the vaccinating provider know so that they can monitor you more closely.

The following history of allergic reactions should be considered in vaccination decisions:

  • If a health care provider diagnoses you as having an immediate allergic reaction of any severity to any ingredient in an mRNA vaccine (including polyethylene glycol or polysorbate), you should not get that vaccine.

  • If a health care provider diagnoses you as having had an immediate allergic reaction of any severity after getting the first COVID-19 shot, you should not get the second shot. Your health care provider may refer you to a specialist in allergies and immunology to provide more care or advice.

  • If you have ever had a previous allergic reaction to a different vaccine or injectable medicine, talk to your health care provider before getting vaccinated. If you decide to get vaccinated, tell the provider giving you the shot so they can monitor you more closely afterward.

Currently Sick with COVID-19

If you know you currently have COVID-19 or symptoms of COVID-19, you should wait until you have recovered and completed isolation to avoid exposing other people at the vaccination site while you are contagious.

This means you should not be vaccinated until all the following are true:

  • At least 10 days have passed since symptoms started (or, if you never had symptoms, 10 days from the date you were tested).
  • You have not had fever for the prior 24 hours without use of fever-reducing medicine.
  • If you had symptoms, your overall symptoms have improved.

Previously Sick with COVID-19

It is possible to get COVID-19 more than once. So even if you previously had COVID-19, you should get vaccinated. Also, the vaccine may boost the protection your body has already built up.

There is no evidence that having had COVID-19 will cause a person to have bad reaction to the vaccine.

Recent Exposure to COVID-19

If you were recently in close contact with someone who has COVID-19 (within 6 feet for at least 10 minutes over a 24-hour period), you should wait to get vaccinated until after you have quarantined for 10 days since you were last exposed.

Other Vaccinations

You should get your COVID-19 vaccine at least 14 days before or after receiving any other vaccines.

Everybody should get both a flu vaccine and a COVID-19 vaccine.

Pregnant or Breastfeeding

People who are pregnant or breastfeeding may choose to be vaccinated.

There is little data on the safety of COVID-19 vaccines in people who are pregnant, as pregnant people were not part of the clinical trials, except for a few who were pregnant and did not know it or later became pregnant.

Similarly, people who were breastfeeding were not included in the clinical trials. However, data suggest COVID-19 is not transmitted through breast milk, and mRNA vaccines are not thought to be a risk to the breastfeeding infant.

If you are trying to become pregnant, you may get vaccinated and you do not need to avoid pregnancy after getting vaccinated.

If you are pregnant or breastfeeding, discuss vaccination with your health care provider.

Autoimmune Disease/Immunocompromised and Underlying Conditions

People who have an autoimmune disease or are otherwise immunocompromised (such as from cancer treatment or other medicine) may choose to be vaccinated. However, people who are immunocompromised were not part of the clinical trials, so there is no data on vaccine safety or effectiveness for this group.

In general, people with underlying chronic and other medical conditions can get vaccinated. Many people who were part of the clinical trials had underlying health conditions and no issues were identified.

If you have concerns about an underlying medical condition, or if you are immunocompromised, discuss getting vaccinated with your health care provider.

Getting Vaccinated


Some people, such as many health care workers and first responders, can get vaccinated by their employer. People who live or work in a group living facility, such as a nursing home, can likely get vaccinated on site.

Vaccines are also available at some hospitals, community clinics and pharmacies, and at City-run vaccination sites around the city. Many sites, including all City-run sites, require an appointment. Appointments are limited based on vaccine supply, so check back often if you do not see one open.

To find a vaccination site:

  • Visit the NYC Vaccine Finder. You can search by address, ZIP code or your current location.

  • If you need assistance making an appointment at a City-run vaccination site, call 877-VAX-4NYC (877-829-4692) and press 1 when asked.

Do not make an appointment unless you are currently eligible to be vaccinated.

Diagnostic/Antibody Testing Not Required Before Vaccination

You do not need to be tested for COVID-19 infection before being vaccinated.

You also do not need to take an antibody test, which checks whether you may have had COVID-19 in the past. Vaccination is recommended for people who previously had COVID-19 even if they test positive for antibodies. It is possible to get COVID-19 again and vaccination may boost your natural immunity.

No Payment or Social Security Number Required for Vaccination

The vaccine is provided at no cost for everyone. You will not need to provide your social security number to get vaccinated.

You will not be charged, even if you do not have health insurance. If you have insurance, bring your insurance card. Your insurance may be billed by the vaccination provider; however, you will not be charged a copay or any other fee.

If someone tries to charge you a fee or asks for your credit card information, or if they ask for your social security number, then it is likely a scam or fraud and you should go elsewhere for vaccination.

Report vaccine fraud or abuse online to the NYS Attorney General (select "File a Complaint"). You can also call 833-VAX-SCAM (833-829-7226) or email

Proof of Eligibility

You will need to show proof of eligibility when you get vaccinated.

Prior to being vaccinated, you will be required to complete the online NYS COVID-19 Vaccine Form, which includes a self-attestation regarding eligibility for vaccination.

Learn more about what you must do to prove you are eligible for a vaccine.

Prepare for Your Vaccine Appointment

There is nothing special you need to do prior to getting vaccinated. Reschedule your appointment if you have any symptoms of COVID-19 or are not feeling well.

Remember to wear a face covering to your appointment and bring:

  • An insurance card if you have one
  • Documents showing you are eligible to be vaccinated (described above)
  • Your vaccination card (second dose appointment only)

How Vaccine Is Given

COVID-19 vaccines are intramuscular vaccines. They are given through a shot in the arm, similar to flu, measles, tetanus and many other vaccines. Both the Pfizer and Moderna vaccines require two doses several weeks apart.

Choosing a Vaccine

The Pfizer and Moderna vaccines are similar and both have been shown to be safe and effective. Both are mRNA vaccines, have similar types of ingredients, require two doses and can cause mild to moderate side effects.

A key difference between the vaccines is the Pfizer vaccine is authorized for people ages 16 and older, while the Moderna vaccine is authorized for people ages 18 and older. Other than that, the main differences between the vaccines have to do with how they are stored and distributed. Vaccination sites will generally only have one of the two vaccines available.

Getting the Second Dose

Both doses should be of the same vaccine. If you receive the Pfizer vaccine, you should get a second dose of the Pfizer vaccine 21 to 42 days after your first dose. If you receive the Moderna vaccine, you should get a second dose of the Moderna vaccine 28 to 42 days after your first dose. You should not get the second dose earlier than recommended.

If you cannot get your second shot during the recommended interval, get it as soon as possible after. No matter how much time has passed, you should still get the second shot. If you get your second shot after the recommended interval, you will still only need two shots in total.

New York State requires people to get their first dose and second dose at the same location.

Vaccination Card

After receiving your first dose, you will receive a card with your name, date of birth, the vaccine you received, and the place and date you received it. Your vaccination card is an important medical record. Keep it in a safe place and make a photocopy or take a picture just in case you lose it.

Bring the card with you when you go for your second shot. If you forget to bring the card or lose it, you will still be able to be vaccinated. The vaccination provider can look up your name in a computer to verify your first vaccination.

If you lose your card, you can get proof of vaccination from the Citywide Immunization Registry. The registry contains records of people vaccinated in NYC, and some records of NYC residents vaccinated outside of the city.

If you have an IDNYC card, you can access your own vaccine record (and your minor children’s records) on the My Vaccine Record website. If you do not have an IDNYC card, your health care provider should be able to access your records and print documentation for you.

Possible Side Effects

Most people report some side effects from the vaccines, which are usually signs that the body is building protection. Common side effects include soreness or swelling on the arm where you got the shot, headache, body aches, tiredness and fever. Get the second shot even if you have side effects after the first shot, unless your health care provider tells you not to get the second dose.

Side effects:

  • Usually are mild to moderate
  • Usually start within the first three days after vaccination (the day after vaccination is the most common) and last for about one to two days after they begin
  • Are more common after the second dose
  • Are less common in older adults

Some symptoms, such as cough, shortness of breath, sore throat and loss of taste or smell, are not reactions to the vaccine. These symptoms could mean you got COVID-19 or another infection prior to being vaccinated or shortly afterwards. If you have one of these symptoms, you should get tested for COVID-19, stay home for work and school, monitor your health and contact your health care provider if needed.

You cannot get COVID-19 from the vaccine.

Managing Side Effects

To reduce pain or swelling at the injection site, put a clean, cool, wet cloth over the area and use or exercise your arm. Call your health care provider if you have any side effects that concern you or do not go away after a few days, or if the redness or soreness where you got the shot increases after 24 hours.

You can also talk to your provider about taking an over-the-counter medicine such as acetaminophen (Tylenol) or ibuprofen (Advil) to relieve pain or discomfort.

Reporting Side Effects

It is helpful to report side effects so public health experts can monitor the effects of the vaccine. This is especially important with a new vaccine. You can report side effects through the CDC’s V-safe smartphone app. You can also report side effects online to the CDC and FDA’s Vaccine Adverse Event Reporting System (VAERS) or by calling 800-822-7967.

Allergic Reactions Are Uncommon

Based on what we currently know, allergic reactions to the vaccine are uncommon.

Allergic reactions generally start within a few minutes to an hour of getting the shot. Signs of a severe allergic reaction can include difficulty breathing, swelling of the face and throat, fast heartbeat, a severe rash all over the body, dizziness and weakness.

If you think you are having a severe allergic reaction, call 911 or go to the nearest hospital.

After Vaccination

When Vaccine Protection Starts

While you may get some protection after the first dose, the vaccines are more effective after two doses. You will not have the vaccine’s full protection until one to two weeks after your second dose.

COVID-19 Test Results

The vaccines do not cause people to have a positive COVID-19 diagnostic (viral) test result. However, it is possible the vaccine can cause you to have a positive antibody test result, since part of the way the vaccines work is to teach your body to produce antibodies to the virus that causes COVID-19.

Keep Taking Precautions

We need to be cautious until more people are vaccinated and until there has been more time for us to better understand the impact of the vaccines on the spread of COVID-19. As such, you must still practice prevention measures even after being vaccinated:

  • Stay home if you are sick or recently tested positive for COVID-19.
  • Stay at least 6 feet away from others.
  • Wear a face covering.
  • Wash your hands often.

Medical and Personal Information Protected

Your personal information is strictly protected. Basic information about you (such as your name, address, phone number, date of birth, vaccination date and vaccine received) will be shared with the NYC Health Department as required by law, but there are strict laws in place to make sure your information remains confidential. Your social security number is not collected or shared, nor is immigration status.

The NYC Health Department is required to send vaccination data to the CDC. Only people’s date of birth, ZIP code, race, ethnicity and gender are shared with the CDC. We will not share any other personal-identifying information, including your name.

Vaccination Requirements

Government and Employers

There are no government requirements for you to get vaccinated against COVID-19.

We do not know what employers may require regarding vaccination.


The vaccines are currently not authorized for use in children (except the Pfizer vaccine may be given to children ages 16 and older), so they cannot be required for school. We do not know yet what will be required for school attendance should the vaccines be approved for children.

Additional Resources