COVID-19 Vaccinations: Frequently Asked Questions (FAQ)

Updated: December 30, 2020

How will we know if a vaccine is safe and effective?

The safety and efficacy of a vaccine is determined through clinical trials. Phase 1 clinical trials assess the safety and dosage of a vaccine in a small number of people, typically a dozen to several dozen healthy volunteers. Vaccine safety is also assessed in Phase 2 studies, in which adverse events not detected in Phase 1 trials may be identified because a larger and more diverse group of people receive the vaccine. However, only in the much larger Phase 3 clinical trials can it be demonstrated whether a vaccine is actually protective against disease and safety more fully assessed. Assessing safety is also a major goal of Phase 3 trials, both short-term safety (e.g., fever, tenderness, muscle aches) and long-term safety (e.g., autoimmune conditions or enhanced disease following infection). After a vaccine is approved and in more widespread use, it is critically important to continue to monitor for both safety and effectiveness. Some very rare side effects may only be detectable when large numbers of people have been vaccinated. (Source: Johns Hopkins University Coronavirus Resource Center)

How long will protection last following vaccination?

We do not know how long protection will last following vaccination. It will be critically important to measure long-term protection in Phase 3 trials and in other groups prioritized for early vaccination (at least two years). We are still learning about the duration of protection following infection with SARS-CoV-2, and it is too early to tell how long protection will last.

There are ways to potentially make protection after vaccination more durable than the protection that follows a natural infection, such as with an adjuvant, which is an ingredient used in some vaccines that helps create a stronger immune response, or with booster doses of vaccine. These strategies to enhance vaccines may be particularly important for vulnerable populations, such as the elderly and those with underlying diseases, who are at particular risk of severe COVID-19 but are also less likely to develop a protective immune response to a vaccine. (Source: Johns Hopkins University Coronavirus Resource Center)

How many shots of the COVID-19 vaccine will be needed?

All but one of the COVID-19 vaccines currently in Phase 3 clinical trials in the United States need two shots to be effective. The other COVID-19 vaccine uses one shot. (Source:

If I already had COVID-19, do I still need to get the 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 — this is called natural immunity. Early evidence suggests natural immunity from COVID-19 may not last very long, and more studies are needed to better understand this. Until we have a vaccine available and the Advisory

Committee on Immunization Practices makes recommendations on how to best use COVID-19 vaccines, we cannot comment on whether people who had COVID-19 should get a COVID-19 vaccine. (Source:

Do I still need to wear a mask and avoid close contact with others if I have had two doses of the vaccine?

Yes. While experts learn more about the protection that COVID-19 vaccines provide under real-life conditions, it will be important for everyone to continue using every available tool to help stop this pandemic: cover your mouth and nose with a mask, wash your hands often, and stay at least 6 feet away from others. Together, the COVID-19 vaccination and following the CDC’s recommendations for how to protect yourself and others will offer the best protection from getting and spreading COVID-19. Experts need to understand more about the protection that COVID-19 vaccines provide before changing their recommendations on the steps everyone

should take to slow the spread of the virus that causes COVID-19. Other factors, including how many people get vaccinated and how the virus is spreading in communities, will also affect this decision. (Source:

What is the difference between a EUA and FDA Approval?

During a public health emergency, the FDA can use its Emergency Use Authorization (EUA) authority to allow the use of unapproved medical products, or unapproved uses of approved medical products, to diagnose, treat, or prevent serious or life-threatening diseases when certain criteria are met, including that there are no adequate, approved, and available alternatives.

The issuance of an EUA allows manufacturers to temporarily circumvent the typical approval process in one of two ways: a manufacturer may distribute an approved product for an unapproved use or temporarily distribute an unapproved product.

To issue an EUA, the FDA along with representatives from a task force of other HHS agency members must find that the following conditions are met:

• The public health emergency identifies a serious or life-threatening disease or condition.

• Based on available quality evidence, it is reasonable to believe that an unapproved product

may be effective in responding to the disease or condition.

• Known potential benefits of the product outweigh known potential risks.

• No adequate FDA-approved substitute exists.

These requirements closely mirror other statutory and regulatory exceptions to the FDA approvals process. Under such conditions, the FDA generally disclaims that unapproved products have not undergone sufficient safety or efficacy testing. The type of review that FDA conducts for an EUA is considerably less rigorous than how the agency would normally review a product for approval. However, under the emergent conditions, they may offer some benefit given the absence of any alternative. (Source:

If I get vaccinated, what will happen with my personal information?

California negotiated a deal with the CDC to limit the personal data shared with the federal government to birth year, sex and the county where the vaccine was administered. State officials say the federal government will not be able to identify the person through that limited data.

But vaccine recipients will still be required to provide more extensive personal information to the California vaccine registry. According to the state’s written vaccine plan, recipients must provide their name, address, sex, date of birth, ethnicity and race. Doctors must also record whether the patient refused the vaccine. The patient information will be collected in California’s Immunization Registry, known as CAIR. (Source: LA Times)

Will the vaccine be effective against the new UK variant?

Viruses constantly change through mutation, and new variants of a virus are expected to occur over time. Sometimes new variants emerge and disappear. Other times, new variants emerge and start infecting people. Multiple variants of the virus that causes COVID-19 have been documented in the United States and globally during this pandemic. Public health officials are studying whether the variants change the effectiveness of COVID-19 vaccines. There is no evidence that this is occurring, and most experts believe this is unlikely to occur because of the nature of the immune response to the virus. (Source:

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