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Frequently Asked Questions About COVID-19 Vaccines


What’s in the vaccine and how does it work?

Four vaccines are currently available. Two vaccines, one by Pfizer and one by Moderna, use messenger RNA (mRNA) technology. This technology does not use any live virus particles. You will not be exposed to the virus that causes COVID-19.

Instead, the vaccines contain instructions for your cells. The messenger RNA -- a piece of genetic code -- tells your cells to make the COVID-19 spike protein themselves. Once your cells make the spike protein, your immune system will create the antibodies that fight COVID-19 and protect you from getting sick from this virus, providing a significant level of immunity.

To be effective, both of the vaccines require you to receive two shots, given a few weeks apart.

A third vaccine, by Johnson & Johnson (J & J), is a viral vector vaccine. It is made from an inactivated adenovirus, the virus that causes the common cold, and contains a piece of DNA that instructs the body to make the COVID-19 spike protein. J & J used a modified adenovirus that can enter cells but can’t replicate inside them or cause illness. This in turn triggers an immune system response, giving you protection should you ever be exposed to the real virus in the future. The use of genetic instructions makes the Johnson & Johnson vaccine similar to, but not exactly the same as the Pfizer and Moderna vaccines.

A fourth, Novavax, is a subunit protein vaccine and requires two shots. It uses “a combination of spike proteins and an immune stimulant to provoke an immune response against the virus that causes COVID-19,” according to Johns Hopkins

Can I get COVID-19 from the vaccine?

No. There are no live virus particles. While you might feel minor, temporary side effects from the injection, it is impossible to contract the virus from the vaccine.

Will the vaccine cause side effects? If so, how long might they last?

Some people who get a COVID-19 vaccine will experience side effects. The side effects of the vaccine appear to be minor and temporary. Participants have reported pain at the injection site, fatigue, occasional fever, headache, or aching muscles and joints. These side effects fade within 1-2 days. 

These side effects are actually common with all vaccines: they are a sign that a vaccine is working and triggering an immune response. If someone is going to have a bad reaction to a vaccine, it is likely to occur in the first six weeks after vaccination.

The only serious side effect, a blood clotting disorder, occurred among 15 women out of the nearly 8 million people who received the Johnson & Johnson vaccine.  A review by a committee of scientific experts concluded that the vaccine is safe for use because the risk is extremely small and the vaccine’s benefits far outweighed its risks. The committee’s review also concluded that failing to use it would lead to many more deaths than the clotting disorder might cause.

If I have side effects from COVID-19 vaccination, can I return to my workplace?

You should be able to return to your workplace after receiving the vaccine. Most people who get the vaccine have few or no side effects. Most side effects are mild, such as discomfort or swelling at the injection site. Some side effects that have been reported in the first few days after each dose, like fever, are normal signs that your body is building protection. These side effects may affect your ability to do some daily activities, but they typically go away within a few hours or days. However, if you experience a fever after vaccination, you may need to stay home from work pending further evaluation, including consideration for COVID-19 testing. 

Learn about the difference between expected side effects and when it may be time to call a doctor. The vaccine will not give you COVID-19. However, you could have been exposed to the virus before getting vaccinated, so if you continue to feel sick, you should talk to your doctor. It takes time for your body to build protection after any vaccination. The COVID-19 vaccine may not protect you until a week or two after your second shot (dose).

Are there any long term side effects?

COVID-19 vaccines are still being tested for long-term side effects. At this point, no long-term safety issues have been detected. The Centers for Disease Control and Prevention (CDC) and the Food and Drug Administration (FDA) are monitoring closely.  As more people get vaccinated, more information will be available in the coming weeks and months. CDC scientists and medical professionals will be continuously reviewing vaccine safety. They will keep providing information to the public and will take action on new safety concerns if needed. 

But even though we are still learning about COVID-19 vaccines, here’s what we do know for sure: getting sick with COVID-19 is dangerous. We know that COVID-19 can cause long-term health problems, even in mild cases.  The CDC has already identified fatigue, shortness of breath, chest pain, coughing and joint pain among the most common reported long-term side effects.  Many people who recover from COVID-19 also suffer from difficulty with thinking and concentration (sometimes referred to as “brain fog”), depression, muscle pain, headaches, intermittent fever and fast-beating or pounding heart (also known as heart palpitations).  

It is unlikely that vaccine-related side effects are riskier than actually having COVID-19.   Given the prevalence of serious side effects from COVID-19 infections and the rarity of long-term side effects from the vaccines, it’s clear that getting vaccinated is the safest choice for the overwhelming majority of people.

Has anyone died or become ill after taking the vaccine?

According to the CDC, COVID-19 vaccines are safe and effective and severe reactions after vaccination are rare. The benefits of COVID-19 vaccination continue to outweigh any potential risks. . There are three vaccines – one is from Pfizer, one from Moderna and one from Johnson & Johnson. Nearly 73,000 individuals took part in clinical trials for the Pfizer and Moderna vaccines and 44,325 individuals took part in the clinical trials for the J & J vaccine. During the clinical trials, there were no deaths, and no reports of severe illness following the vaccination.

How effective is the vaccine?

All four vaccines have a very high level of effectiveness: Pfizer has a 95 percent rate and Moderna has a 94 percent rate. That means that among people who took the vaccines, there were 94 to 95 percent fewer cases of COVID-19 than among those who did not receive it. The J & J vaccine was 85% effective in preventing severe/critical illness and 66% effective in preventing symptomatic illness 28 days after vaccination. Importantly, it was 100% effective in preventing hospitalization and death from COVID-19.

While it’s difficult to compare vaccines for different diseases, for context, flu vaccines are only 40-60% effective in any given year. The high level of effectiveness of the COVID-19 vaccines means they haves the potential to significantly prevent the spread of the disease.

Does the vaccine protect against the Delta and Omicron variants?

Vaccines can prevent or reduce the severity of nearly every variant of COVID-19, including the Delta and Omicron variant. There is also vaccine development underway to target Omicron.

Is one vaccine better at protecting against COVID-19 than the other?

No. Pfizer and Moderna use the same mRNA technology, and they have similar levels of effectiveness: among people who took the vaccines, there were 94 to 95 percent fewer cases of COVID-19 than among those who did not receive it. To be effective, both of the vaccines require you to receive two shots, given a few weeks apart.

The Johnson & Johnson vaccine was 85% effective in preventing severe/critical illness and 66% effective in preventing symptomatic illness 28 days after vaccination. Importantly, it was 100% effective in preventing hospitalization and death from COVID-19. The J & J vaccine requires only one dose.

For the Norovax vaccine, both phase 2 trials found that the efficacy of the vaccine against mild, moderate, and severe disease was 90%.

Vaccine distribution sites may administer one of the four authorized vaccines, depending on their supply. If you receive the Pfizer or Moderna vaccine for your first shot, both of which require two doses, you cannot get a second shot from a different vaccine.

How many doses do I need to be fully protected? Is one dose good enough?

To be effective, the Pfizer ,Moderna and Norovax vaccines require two shots, given a few weeks apart. It is typical for the second dose of vaccine to give a more significant, longer-term boost. Giving a vaccine in two doses is common for many childhood vaccines. The first shot primes the immune system, helping it recognize the virus, and the second shot strengthens the immune response. Pfizer’s second shot is given 21 days after the first one; Moderna’s is 28 days later.

If you receive the Johnson & Johnson vaccine, you will only need one dose.  

Your vaccine provider should tell you which vaccine you received and whether you need to come back for a second dose – but if you’re not sure, don’t be afraid to ask.

How will I remember to get the second shot?

Each person getting the Pfizer or Moderna COVID-19 vaccine will receive a vaccination record card to make sure they receive the correct vaccine for the second dose. You can also enroll in v-safe, a smartphone-based tool that uses text messaging and web surveys to provide personalized health check-ins after you receive a COVID-19 vaccination. V-safe will remind you to get your second COVID-19 vaccine dose if you need one.

What if I miss my second shot?

Some people who receive the first dose of Pfizer or Moderna COVID-19 vaccine may not be able to receive the second dose when their employer offers it. In those cases, they may complete the vaccine series by bringing their vaccination record card to another location in their area that is administering the vaccine. You should not need to restart your series of shots. It is important that you get the same vaccine for both your first and second dose.

Can I mix and match vaccines?

No. For a two-dose vaccine, your second dose must be from the same vaccine as the first. Since the vaccines differ in composition, storage and time between the two doses, experts say people must take the same vaccine for both doses.

How long does the protection last? Will I need to get a booster shot every year?

It’s possible you may need to continue to get booster shots. Because the disease is new, we still have more to learn about how long immunity might last. The protection may wane over time, and you may be susceptible again. It’s also possible that the virus could mutate. Public health experts and scientists will continue to study the virus and monitor people’s immunity, and issue guidance accordingly in the future. While likely years away, there are also efforts to develop vaccines that might remove the need for a booster.

Can I still get the virus, even if I take the vaccine?

Yes. It typically takes a few weeks for the body to build immunity after vaccination. That means it’s possible a person could be infected with the virus that causes COVID-19 just before or just after vaccination and get sick. This is because the vaccine has not had enough time to provide protection.

While the vaccine provides significant protection, it is not 100% effective. There is a slight chance you may still get infected, but it will most likely be a mild case of the virus as opposed to a severe case which is possible without the vaccine. Contracting the virus without protection can have potentially deadly consequences – taking the vaccine does not.

Can I still spread the virus, even after getting vaccinated?

We don’t yet know whether vaccinated individuals can spread the virus to others who may not have received the vaccine. That’s why it will be critical that everyone continues to wear masks, socially distance and follow all the necessary public health protocols both at work and elsewhere.

Does the vaccine work better depending on a person’s age, weight or race?

Based on the available data, we know that all four vaccines work regardless of age, weight or race. Trials for the Pfizer and Moderna vaccines included over 25,000 people from the communities most impacted by COVID-19, including Black, Latinx, and older people. The Johnson & Johnson vaccine was tested on 44,325 participants including Black, Latinx, AAPI and older people.

I have pre-existing conditions. Will taking the vaccine have harmful effects?

We don’t yet know for certain how individuals with different pre-existing conditions will react to the vaccine.  It is clear, however, that those with other health complications are at a higher risk for contracting severe cases of COVID-19. If you have a pre-existing condition, you should consult your doctor on what’s best for you.

I have allergies. Can I still take the vaccine?

Some people may be at risk for an adverse reaction because of an allergy to one of the vaccine components or a medical condition. CDC provides recommendations for people who have had allergic reactions to other vaccines and for those with other types of allergies.

Is it safe to get the vaccine if I’m pregnant or breastfeeding?

There is limited information about the safety of COVID-19 vaccines during pregnancy and breastfeeding. However, based on knowledge about how these vaccines work, experts believe the vaccines are unlikely to pose a risk for pregnant women or breastfeeding infants. Pregnant and breastfeeding women may choose to be vaccinated if they are part of a group that is recommended to receive COVID-19 vaccine. Your doctor can help you make this decision.

Is it safe for me to get the COVID-19 vaccine if I would like to have a baby one day?

Women who are trying to become pregnant do not need to avoid pregnancy after receiving a COVID-19 vaccine. Scientists study every vaccine carefully for side effects immediately after vaccination and for years afterward. There is no evidence that fertility problems are a side effect of any vaccine.  In fact, some vaccine trial participants became pregnant during the vaccine trials.

Will the COVID-19 vaccine change my DNA?

No. Some of the COVID-19 vaccines are a new type of vaccine called “messenger RNA” vaccines or “mRNA” vaccines. Messenger RNA vaccines teach our cells how to make a protein—or even just a piece of a protein—that triggers protection inside our bodies. The mRNA in the vaccine cannot affect your DNA in any way.

Our DNA is in the nucleus of our cells. Both of these new vaccines are made of small bits of genetic material called M, or messenger, RNA. M-RNA is a normal part of the cell’s machinery that’s made in the nucleus and travels out to the rest of the cell to do its work – making proteins. But that’s a one-way street from the nucleus, out. The M-RNA in the vaccines also does its work in the part of the cell outside the nucleus. It never gets near the DNA in your cells.

I already had COVID-19 – do I still need a vaccine?

There is not enough information currently available to say if or for how long after infection someone is protected from getting COVID-19 again. Early evidence suggests that natural immunity from COVID-19 may not last very long, but more studies are needed to better understand this. The CDC has not issued a recommendation on whether people who had COVID-19 should get a COVID-19 vaccine and you should talk to your doctor to find out more about what’s best for you.

I haven’t gotten a flu shot yet. Should I?

Yes. Getting a flu vaccine is an essential part of protecting your health and your family’s health this season. Flu vaccines are useful any time during the flu season and you can often get them in January or later. 

A flu vaccine will not protect you from getting COVID-19, but it can prevent you from getting influenza (flu) at the same time as COVID-19. This can keep you from having a more severe illness and needing medical care. Flu is another serious respiratory illness that can cause missed work, hospitalization, and, in some cases, even death. 

You should wait at least 14 days after getting the COVID-19 vaccine to get a flu shot.

Will I still need to wear PPE and follow public health protocols even after getting the vaccine?

Yes. We will still need to wear masks and practice physical distancing until a large proportion of the population is vaccinated and we are sure the vaccine provides long-term protection – and your employer should ensure you have this equipment readily available at work. Initially, there will not be enough vials to vaccinate everyone who wants the vaccine and the virus will still be transmitted.

While the vaccine provides significant protection, it is not 100% effective. We also don’t know whether vaccinated individuals can still carry and spread the virus to people who haven’t been vaccinated. Everyone should continue to wear PPE and follow public health protocols both at work and elsewhere.

In fact, when you get the vaccine, you and the person administering the vaccine will both need to wear masks.  The CDC recommends that during the pandemic, people wear a mask that covers their nose and mouth when in contact with others outside their household, when in healthcare facilities, and when receiving any vaccine, including a COVID-19 vaccine.

Should I get a booster?

Below are the CDC's recommendations:

One booster:

  • Everyone ages 5 years and older should get 1 booster after completing their COVID-19 vaccine primary series, if eligible.

Two boosters:

  • Adults ages 50 years and older

  • Some people ages 12 years and older who are moderately or severely immunocompromised


The vaccines were made so quickly. How do I know it is safe and not rushed?

The mRNA vaccines produced by Pfizer and Moderna are faster to develop because they are not using live virus particles. Instead, the mRNA is easy to make in the laboratory – saving several years for development. 

These vaccines are carefully studied, tested, and regulated before they can be used. The companies that created the vaccines submit extensive applications to multiple government agencies and independent bodies of scientific experts, which will only permit the vaccine to be used if the evidence shows it is safe.

Healthcare workers will be among the first who can take the vaccines. How robust were the trials? How many people were involved and how thorough was the study?

In clinical trials for the vaccine candidates from Pfizer and Moderna, over 73,000 people from the U.S. and around the world received injections of the vaccine. Both vaccines have a very high level of effectiveness.

Did the clinical trials for the vaccines from Pfizer and Moderna include people from the groups most affected by COVID-19, especially Black, Latinx, and older people?

Yes. While vaccines work the same in people of different races or ethnicities, it is important to make sure vaccines are tested in diverse population groups before they are released. The clinical trials conducted by Pfizer and Moderna included over 25,000 people from the communities most impacted by COVID-19, including Black, Latinx, and older people.

How does the vaccine approval process work?

In the United States, vaccines must be approved by the Food and Drug Administration (FDA) before they can be used. The FDA bases its decision to approve or not approve a vaccine on data from clinical trials. The data is reviewed by independent experts who are not part of the government or the pharmaceutical companies, and by career scientists and physicians at the FDA who are not politically appointed and who are experts in vaccine safety and effectiveness.

The scientists look out for unexpected side effects that the vaccine might have caused. This helps determine the vaccine’s “safety.” In general, the fewer and less severe the side effects are, the more the vaccine is considered safe. If the clinical trial data shows enough evidence of efficacy and safety, the FDA will approve the vaccine and license it for use in the United States.


Can my employer require that I get the vaccine?

In general, employers may require employees to receive a vaccination (i.e. the flu vaccine) under certain circumstances.  Employer authority to implement and enforce a mandatory vaccination program has several limitations. Under federal anti-discrimination laws, employees may refuse a mandatory vaccine on the basis of a disability or a sincerely held religious belief.  Further, employers may commit an unfair labor practice if they fail to bargain with the union before implementing a mandatory vaccination program.

However, SEIU members are encouraged to take it given their efficacy in reducing serious illness, long -term complications from the virus--and to protect loved ones and neighbors.  When the virus is allowed to spread and replicate, it mutates.  These changes potentially make it more resistant to vaccines.  By taking the vaccine, SEIU members can help prevent this.  Mass vaccination is the best way to stop the spread of COVID-19, save lives and begin to resume normalcy once again.

Will those who are vaccinated be assigned to work with patients with COVID-19 more frequently?

No, the immunization status of a healthcare worker will not affect his/her work assignment.

Is the vaccine free? Will my insurance cover it?

You will not have to pay for the vaccine. The vaccine itself is free, and Medicare, Medicaid, and Private Insurance have agreed to offer it for free. Individuals who are uninsured may incur a cost for vaccine administration. 

Can I get vaccinated even if I don’t have a Social Security number?

Everyone in the United States is eligible for vaccination against COVID-19.  The Biden Administration has announced that no immigration enforcement efforts will be conducted in relation to the vaccine and all personal information will remain private.  Some state and local registration forms ask for a Social Security number, however people may enter 0s in lieu of a Social Security number if they do not have or know the registrant’s number.

Will I have a chance to take the vaccine later if I decline the first opportunity?

We don’t have all the details yet on how many doses will be available in the initial distribution. Due to limited doses of the vaccine, choosing not to take it when it is first available may mean you will have to wait many more months to have an opportunity to do so again.

*Thanks to SEIU 1199UHE for developing this fact sheet, in close
consultation with doctors and other medical professionals.

Updated Sep 23, 2022