Vaccine Effectiveness FAQ


I am nervous about getting the vaccine. Why should I get it?

It is normal to feel uneasy or unsure about getting a new vaccine. But the benefits of getting the COVID-19 vaccine and helping to end the pandemic far outweigh the risks.

  • Worry less. Getting vaccinated against COVID-19 can lower your risk of getting and spreading the virus that causes COVID-19. Vaccines can also help prevent you from becoming seriously ill, hospitalized, or dying due to the COVID-19 virus.
  • All steps have been taken to ensure that vaccines are safe and effective for people ages 6 months and older.
  • If you already had COVID-19, you should still get a COVID-19 vaccine for added protection.
  • When you are up to date on COVID-19 vaccination, you can resume many activities with proper precautions.

We are all in this together, and for every person that gets the vaccine, we are one step closer to ending the pandemic.

What is the difference between "up to date" and "fully vaccinated"?

  • Up to date means a person has received all recommended COVID-19 vaccines, including any booster doses, when eligible.
  • Fully vaccinated means a person has received their primary series of COVID-19 vaccines. Everyone is considered fully vaccinated 2 weeks after their second dose in a 2-dose series, such as the Novavax, Pfizer-BioNTech, and Moderna vaccines, or 2 weeks after the single-dose Johnson & Johnson Janssen vaccine, except for immunocompromised patients.

For more information, please refer to the Stay Up to Date with Your Vaccines Including Boosters page on the CDC website.

Do I need to continue wearing my mask if I am up to date on my COVID-19 vaccinations?

According to the Centers for Disease Control & Prevention (CDC), when you are up to date on COVID-19 vaccination, you can resume many activities with proper precautions.

When you are up to date on COVID-19 vaccination, you may not always need to wear a mask in public.

  • In general, you do not need to wear a mask in outdoor settings.
  • If you are in an area with a high COVID-19 Community Level, wear a mask indoors in public.
  • If you are immunocompromised or otherwise at risk for severe disease, talk with your healthcare provider about wearing a mask indoors at medium COVID-19 Community Levels.
  • You may choose to wear a mask at any time.

Dartmouth Hitchcock Medical Center and Dartmouth Hitchcock Clinics continue to require mask use at all times in all facilities, without regard to vaccination status. Our policy will continue to apply to all of our staff, patients, visitors, and any others entering our facilities.

Please refer to these CDC links for up-to-date mask recommendations based on COVID-19 Community Levels:

Businesses and organizations may continue to require masks in order to keep their customers and employees safe. You should follow the rules established by those entities. In addition, many people have become used to wearing masks and will choose to continue to "mask up" to keep themselves, and others, safe. Remember that none of the vaccines are 100% protective and there are still large segments of our populations that have not achieved immunity. It is reasonable to choose to continue to wear a mask, even if you are vaccinated.

How effective is the vaccine, and when does the vaccine protection begin?

All 4 vaccines have been shown to be safe and effective against COVID-19, even with new variants emerging.

Based on manufacturer data:

  • The Janssen vaccine was found to be 66.3% effective against symptomatic COVID-19 and 93.1% effective in preventing hospitalizations at 14 days after vaccination.
  • The Novavax vaccine is reported to be 90% effective at creating an immune response against the Omicron variant 2 weeks after the final dose in the primary series.
  • The Moderna vaccine was found to be 94.1% effective against COVID-19 after receiving 2 doses and 100% effective against severe COVID-19 disease.
  • The Pfizer-BioNTech vaccine was found to be 94.6% effective against COVID-19 beginning 7 days after the second dose.

While reports have suggested lower rates of protection against symptomatic disease from emerging variants, all available vaccines remain highly protective against severe disease and hospitalization. 

You can find additional information about effectiveness on the vaccine fact sheets.

Are COVID-19 booster shots necessary?

Yes. Studies continue to demonstrate the importance of vaccination and booster doses to protect individuals from infection and severe outcomes of COVID-19.

  • Although COVID-19 vaccines remain effective at preventing severe disease, recent studies suggest their effectiveness at preventing infection or severe illness decreases over time, especially in people ages 65 years and older.
  • During the recent Omicron surge, those who were boosted were 21 times less likely to die from COVID-19 compared to those who were unvaccinated, and 7 times less likely to be hospitalized.
  • The CDC continues to recommend that all eligible adults, adolescents, and children ages 6 months and older be up to date on their COVID-19 vaccines.

Read more information about booster shots from the Centers for Disease Control & Prevention (CDC).

Could I test positive for COVID-19 after receiving the vaccine?

No, not as a result of the vaccine alone. The vaccines won't cause you to test positive on viral tests. If your body develops an immune response, which is the goal of vaccination, there is a possibility you may test positive on some antibody tests.

Will there be a test for immunity as a result of the vaccine?

No, testing for immunity is not recommended. There are 2 antibody tests currently in use nationally. One test will generally only detect the type of antibody that is produced by natural infection, not antibodies produced by a response to vaccination. The other test is unable to distinguish between antibodies produced by the vaccine or by natural infection. Given the experience with the COVID-19 vaccine so far, experts are confident in the protection provided even if you experience little to no side effects from the vaccine.

Is it better to get natural immunity to COVID-19 rather than immunity from a vaccine?

No. While having the COVID-19 infection does give some immunity, it is a dangerous option, causing serious illness in many, with debilitating symptoms that can last for months. And it kills at least 1-2% of those who get it. Also, experts think immunity from the disease itself may not be long-lasting. Vaccination is the best protection; it is very safe and provides the best immunity.

Getting vaccinated against COVID-19 is a safe way for your body to build immunity by creating antibodies to the virus than having you get sick with COVID-19 and develop a severe infection.

Where can I learn more about the vaccines?

You can find additional information about effectiveness on the vaccine fact sheets: