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COVID-19 Vaccine FAQs

How do we know if COVID-19 vaccines are safe?

COVID-19 vaccines were tested in large clinical trials to make sure they meet safety standards. More than 73,000 people (43,000+ for the Pfizer-BioNTech vaccine and 30,000+ for the Moderna vaccine) were recruited to participate in these trials to see how the vaccines offer protection to people of different ages, races, and ethnicities, as well as those with different medical conditions. There were no serious safety concerns in vaccine recipients compared to placebo study subjects.

Do the COVID-19 vaccines have side effects?

Most people do not have serious side effects after being vaccinated. However, your arm may be sore, red, or warm to the touch and some people report getting a headache or fever after getting a vaccine. These are more common following the second dose of the vaccine. The symptoms usually go away on their own within 1-2 days. You may take acetaminophen as needed to relieve these symptoms. These side effects are a sign that your immune system is doing exactly what it is supposed to do. It is working and building up protection to disease.

Is it better to contract COVID-19 and gain immunity or get the vaccine?

Both this disease and the vaccine are new. We don’t know how long protection lasts for those who get infected or those who are vaccinated. What we do know is that COVID-19 has caused very serious illness and death for some people and prolonged illness in others. If you get COVID-19, you also risk giving it to loved ones who may get very sick. Getting a COVID-19 vaccine is a safer choice to avoid the risk of serious illness.

How many doses are needed and why?

The recently approved Emergency Use Authorized Pfizer vaccine, and Moderna vaccine pending formal FDA evaluation, both require two shots. The same vaccine brand must be used for both shots. The first shot starts building protection, but everyone has to come back 21 days later for the second one to get the most protection the vaccine can offer.

How is priority for COVID-19 vaccinations determined?

Initially the vaccine supply will be very limited. California is making sure that these supplies are distributed and administered equitably. At first, vaccines will be provided to healthcare workers and long-term care residents in accordance with the California Department of Public Health’s Guidelines for COVID-19 Vaccine During Phase 1A. This will be followed by essential workers, who are Californians critical to our daily existence and those at highest risk of becoming infected, severely ill, or spreading COVID-19. The phased rollout to priority recipients and the general public is expected to take about six months. Learn more about phasing from the California Department of Public Health here.

Can the COVID-19 vaccine give me COVID-19?

COVID-19 vaccinations can’t cause COVID-19, as they contain no infectious COVID-19 virus. The goal of the vaccines is to teach our immune systems how to fight the virus that causes COVID-19.

Can the COVID-19 vaccines cause me to test positive on COVID-19 viral tests?

Vaccines won’t cause you to test positive on viral tests, which are used to see if you have a current infection. They will produce positive results in antibody tests that detect the COVID-19 spike protein, but not in antibody tests that solely detect COVID-19 nucleocapsid protein.

Will the vaccine prevent me from contracting and spreading COVID-19 to others?

Unfortunately, no vaccine is 100% effective, but the Pfizer and Moderna vaccines are over 90% effective in preventing symptomatic disease. Their efficacy in preventing asymptomatic disease and disease transmission requires further study.

Should I get the vaccine if I have already had and recovered from COVID-19?

Yes, you should still receive the COVID-19 vaccine if you have already recovered from having the virus. There is not enough information currently available to say if or for how long after infection someone is protected from getting COVID-19 again; this is called natural immunity. Early evidence suggests natural immunity from COVID-19 may not last very long, but more studies are needed to better understand this. At present persons who have recovered from COVID-19 may wait up to 90 days from illness to be vaccinated, but may receive the vaccine earlier as well.

Will I still need to wear when I’m in the community or around people outside of my household?

Yes. How much protection the COVID-19 vaccines provide under real-life conditions is still unknown. We need to understand more about the protection that COVID-19 vaccines provide before we change recommendations on mask use. It is important for everyone to continue using all the tools available to us to help stop this pandemic, like:

Who should not get a COVID-19 vaccine?

At this time the following groups should not get the COVID-19 vaccine:

  • Children under the age of 16;
  • People with current COVID-19 infection requiring isolation;
  • People who have received COVID-19 convalescent plasma or COVID-19 monoclonal antibodies within the last 90 days; and
  • People who have had anaphylactic reactions to any vaccines or injection medication should not receive the Pfizer-BioNTech vaccine.

Can the vaccine be given to immunocompromised persons and others with chronic illness?

The COVID-19 vaccine can be given to immunocompromised persons and people with chronic illness, as long as they do not have conditions listed above for persons who should not get the vaccine. People with chronic illnesses were included in COVID-19 vaccine studies and had no evidence of increased toxicity or decreased efficacy of the vaccine. Immunocompromised persons may have less vaccine-induced protection from COVID-19 vaccine and should continue post-vaccination to take precautions to protect themselves from COVID-19 infection.

What about COVID-19 vaccine in pregnant or breastfeeding women?

While pregnant and breastfeeding were not included in the initial large studies of COVID-19 vaccine, studies are underway in these groups. There are no known risks of mRNA vaccines to pregnant or a breastfeeding infant. Pregnancy itself increases the risk for severe COVID-19 infection and COVID-19 infection may increase the risk of some pregnancy complications. Pregnant or breastfeeding women should discuss with their physician their risk of COVID-19 infection and its complications in the context of the uncertain risks and benefits of COVID-19 vaccine for themselves and the fetus/infant.

Does the Pfizer-BioNTech COVID-19 vaccine contain preservatives or latex?

The vaccine does not contain mercury, aluminum, benzoate, other preservatives, or latex. It consists of a mixture of lipids (fat molecules), salts, sugar, water, and the modified messenger RNA of the COVID-19 spike protein. To view the full list of ingredients in the vaccine, visit: (see page 2).

Can I get Bell’s Palsy from the COVID-19 vaccine?

In vaccine studies, 30,000+ study subjects were followed for over nine weeks (post-second vaccine). From this group, three cases of Bell's Palsy were reported in participants who had the vaccine and one case reported in a participant who had the placebo. The difference between the two groups can occur by chance (Pearson or Yates Chi square test) 30-60% of the time. The expected cases of Bell's Palsy in a population of 30,000 in approximately three months is 1-4 cases. As such, the study findings reported are unlikely to be caused by the vaccine, and are consistent with the expected number of cases of Bell's Palsy in 30,000 people over 3 months.

Sources: Centers for Disease Control and Prevention and California Department of Public Health