Vaccination FAQs

​​​​1. What does Emergency Use Authorization (EUA) mean? 

The FDA ensures medical products are safe and effective for us to use. FDA approval can often be a long process. EUA helps the FDA provide faster access to medical products during a health emergency. It balances known risks and benefits to the public. 

EUA helps when there are no other adequate, approved, and available options. EUAs may change as the FDA completes approvals, clears, or licenses the medicines or treatments. 

You can learn more about EUAs on the FDA’s website. 

2. Are these vaccines safe? 

Safety is a top priority. The U.S. vaccine safety system ensures that all COVID-19 vaccines are as safe as possible. 

COVID-19 vaccines are carefully looked at in clinical trials with thousands of people. In each of these trials, people are closely checked for any health risks. Once the trial results indicate the vaccine is safe and effective, it can be authorized by the FDA. 

Checks on the vaccine will continue in the real-world setting. These can help researchers know if there might be very rare side effects or long-term risks not seen in trials.  

Also, California has formed a Scientific Safety Review Workgroup to look at data to help ensure the COVID-19 vaccine meets safety requirements.  

Read this fact sheet about the vaccines. You can also read this article about safety and efficacy. 

3. How were these vaccines developed so quickly?

The SARS (severe acute respiratory syndrome) outbreak in 2002 was the first coronavirus epidemic to arise out of nowhere. Then in 2012 MERS hit and scientist took notice. SARS, MERS and COVID are all part of the coronavirus family with the same spike proteins. Since 2012, scientists have been researching and developing potential coronavirus vaccines which laid the groundwork for our current COVID-19 vaccines. So, in reality, it’s been about 10-15 years of research and development on the various COVID-19 vaccines. (See link with video) 

The speed to development of these vaccines may seem fast. But there was no cutting corners. The apparent speed comes from worldwide collaboration between: 

      • Scientists, 
      • Pharmaceutical companies, and 
      • New technologies 

The U.S. government was able to help aid faster development, too. It worked closely with pharmaceutical companies and supported swift distribution efforts. 

All vaccines come with side effects or some risk. But the FDA, in authorizing the COVID-19 vaccines, concluded that their benefits outweighed their risks.

4. Are these vaccines effective? 

Each authorized vaccine has been found to be effective in protecting against COVID-19. What we know today is that these vaccines decrease: 

      • Risk of getting COVID-19, 
      • Severe illness or hospitalization as a result of COVID-19, and 
      • Death from COVID-19. 

Compare that to the annual flu vaccine, which is between 40% and 60% effective at reducing the risk of flu illness. 

Bottom line: In the clinical trials, all three COVID-19 vaccinations resulted in: 

Extremely rare deaths from COVID-19, and Dramatically reduced hospitalizations from COVID-19. 





95% after 14 days from the second dose 



94% after 14 days from the second dose 


Johnson & Johnson 

85% at preventing severe illness after 28 days from a single dose 


You can learn more about safety and effectiveness in our article. 

One common misunderstanding is that 95% efficacy means that in the Pfizer clinical trial, 5% of vaccinated people got COVID. But that's not true; the actual percentage of vaccinated people in the Pfizer (and Moderna) trials who got COVID-19 was about a hundred times less than that: 0.04%. What the 95% actually means is that vaccinated people had a 95% lower risk of getting COVID-19 compared with the control group participants, who weren't vaccinated. In other words, vaccinated people in the Pfizer clinical trial were 20 times less likely than the control group to get COVID-19. 

5. How is the Johnson & Johnson vaccine different from the Pfizer and Moderna vaccines? 

Unlike the Pfizer and Moderna vaccines, which are mRNA vaccines, the Johnson and Johnson vaccine: 

      • Is a single-dose vaccine, 
      • Can be stored in a standard refrigerator, 
      • Offers faster protection, 
      • May limit the spread of the virus, and 
      • Uses viral vector technology, a common cold type of virus that has been modified so it cannot cause disease to carry genetic material into cells that then leads to the cell making antibodies to fight infection. 

This means this particular vaccine can be distributed to more people more quickly. In turn, this may help us get to herd immunity faster.

6. What are the ingredients in the COVID-19 vaccines? 

The ingredients in the Pfizer and Moderna vaccines include pieces of mRNA, lipids, salts, sugars, and buffers. These ingredients help make the solution stable and get into cells where they need to be to work.   

The Johnson & Johnson vaccine includes a common cold type of virus that has been modified so it cannot cause disease (the viral vector). This allows the genetic material placed inside the viral vector to create the spike proteins that then lead to making antibodies. As with the other vaccines, there are buffers and other ingredients to help make the solution stable.   

These vaccines do not contain: 

      • Eggs, 
      • Preservatives, or 
      • Latex. 
You can find a full list of the ingredients for all the authorized COVID-19 vaccines at the CDC’s website: 

In a single year, COVID-19 became a leading cause of death in the United States. The vaccines are 100% effective at preventing death from COVID-19. The risks are far less than getting sick from COVID-19 Getting the vaccine will help protect you and your loved ones from the risk of getting COVID-19. The more people who get vaccinated, the more we can reduce restrictions and return to “normal” daily life. The pandemic has also had major impacts on local and national economies. Getting vaccinated is the first step to ending the pandemic. It puts us on the road to faster economic recovery. 

Learn more about the benefits of vaccination from the Centers for Disease Control and Prevention (CDC). 

8. How many COVID-19 vaccine doses do I need? When do I need them? 

This varies by vaccine. 






21 days apart 



28 days apart 

Johnson & Johnson 




If you skip the second shot of the two-dose vaccines, you will not have the full protection that the vaccine offers. It is important to get both shots for Pfizer and Moderna to be fully protected. 

9. Are there side effects to the COVID-19 vaccines? 

Yes. Side effects are normal with most vaccines and are usually mild. Reported side effects include: 

  • Fatigue 
  • Fever 
  • Chills 
  • Headache 
  • Muscle aches 
  • Joint pain 
  • Pain at the injection site 
  • Nausea 

These symptoms are signs that the body is building immunity. They may be uncomfortable. The good news is these side effects don’t last long.  

Severe allergic reactions to the COVID-19 vaccines are extremely rare and have not resulted in any deaths. 

If you received a Johnson & Johnson vaccine in the past three weeks, please also watch for these rare blood clot symptoms. These include: 

  • severe or constant headache or blurred vision, 
  • persistent abdominal pain, 
  • leg pain or swelling, 
  • chest pain, 
  • shortness of breath, and 
  • easy bruising or tiny blood spots under the skin beyond the site of the injection. 


If you develop any of the above symptoms after receiving the Johnson & Johnson vaccine, contact your healthcare provider right away. 

10. How long does it take to be protected after vaccination? 

Protection from the vaccines is not immediate and varies by type. In most cases, it will take one to two weeks following the full dose to get the most protection the vaccine can offer. 

As the Johnson & Johnson vaccine is a single shot, it provides the quickest protection. 

For the two-dose Pfizer and Moderna vaccines, some protection begins building after the first shot (about 50% effectiveness two weeks after the first dose). But you’ll get the most protection one to two weeks following the second dose. 





5 weeks after first dose 

3 weeks 


6 weeks after first dose 

4 weeks 

Johnson & Johnson 

5 weeks after first and only dose 

No waiting period 

11. I heard there are new COVID-19 strains. Are the vaccines effective against them? 

All viruses change (mutate) over time. COVID-19 is no exception. Most mutations have little to no impact on how a virus behaves. They disappear over time.  

Of the COVID-19 strains that have mutated, three have become the primary focus of health experts: "UK," "Brazil," and "South Africa."  The CDC and California Department of Public Health (CDPH) are tracking these new strains. A new variant found in California is also being tracked. Read more in our article about the new strains. 

Early results suggest the vaccines offer strong protection against the UK strain but somewhat less protection against the South Africa strain. Even if vaccines are less effective against some strains, they are still worth getting. This is because they make infections less serious. 

In other words, if you are vaccinated your symptoms may be milder if you get the virus. 

Continue to follow the preventive measures recommended. These are also effective against the new variants: 

  • Staying home except for essential activities 
  • Wearing a mask when leaving home 
  • Limiting interactions with people outside your immediate household 
  • Keeping a physical distance of at least six feet apart 
  • Washing hands for 20 seconds 
  • Getting the COVID-19 vaccine when it’s available to you 

12. Vaccinated - now what?  

A growing body of evidence suggests that fully vaccinated people are less likely to have an asymptomatic infection and potentially less likely to transmit SARS-CoV-2 to others. However, further investigation is ongoing. For more details, you can check this link:  

If you’ve been fully vaccinated: 

  • You can resume activities that you did prior to the pandemic. 
  • You can resume activities without wearing a mask or staying 6 feet apart, except where required by federal, state, local, tribal, or territorial laws, rules, and regulations, including local business and workplace guidance. 
  • If you travel in the United States, you do not need to get tested before or after travel or self-quarantine after travel. 
  • You need to pay close attention to the situation at your international destination before traveling outside the United States. 
  • You do NOT need to get tested before leaving the United States unless your destination requires it. 
  • You still need to show a negative test result or documentation of recovery from COVID-19 before boarding an international flight to the United States. 
  • You should still get tested 3-5 days after international travel. 
  • You do NOT need to self-quarantine after arriving in the United States. 

If you’ve been around someone who has COVID-19, you do not need to stay away from others or get tested unless you have symptoms.  

However, if you live or work in a correctional or detention facility or a homeless shelter and are around someone who has COVID-19, you should still get tested, even if you don’t have symptoms.​ ​