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Once You’ve Been Vaccinated Against COVID-19, How Protected Are You?

May 17, 2021

As COVID-19 vaccinations continue to roll out across the country, you may have questions about how the vaccines work. You may also wonder how protected you’ll be to the virus that causes COVID-19 after you’re vaccinated. We’ll give you the answers based upon recent studies and rigorous research.

Currently, three vaccines are available in the United States, authorized by the U.S. Food and Drug Administration (FDA) for emergency use. Each of the vaccines works a little differently. Two of the vaccines, from Pfizer-BioNTech and Moderna, require two doses spaced apart over the course of several weeks. The most recently authorized vaccine, from Johnson & Johnson/Janssen Pharmaceuticals, requires a single dose.*

How and when do you become immune through vaccination?

Many myths about vaccines abound, but they have consistently proven safe. Vaccinations work with our immune systems by introducing an inactive or weakened form of a virus or bacteria to our bodies. This teaches our bodies to recognize and fight a virus.

With the new COVID-19 vaccines, it takes two weeks for the body to build full protection, or immunity. For vaccines requiring multiple doses, such as the Pfizer and Moderna vaccines, that two weeks starts after the final dose. After the second dose, studies have shown that the vaccine is around 95% effective in protecting you from COVID-19. While you do develop some immunity after the first dose, it is critical to receive both doses of the Pfizer and Moderna vaccines.

It is also very important to continue social distancing and safe practices while your body builds up protection. You can still contract COVID-19 before or just after the vaccination because your body does not have enough time to build immunity, and no vaccine is 100% effective in protecting against infection. You are considered fully protected two weeks after the last dose of the two-dose vaccines, or fully protected two weeks after the Johnson & Johnson/Janssen single-dose vaccine. If it has not been two weeks, you are not fully protected.

While scientists know the COVID-19 vaccines work to keep you safe, they are still learning how well the vaccines prevent the spread of COVID-19 to others. They are also not sure how long the protection lasts. Until they learn more, it is important to continue to take precautions in public places even after you have been fully vaccinated. Frequent handwashing, staying six feet apart, masks that cover your nose and mouth, and continuing to avoid large gatherings are critical in the fight against COVID-19.

According to the CDC, fully vaccinated people can resume activities that you did prior to the pandemic without wearing a mask or physically distancing, except where required by federal, state, local, tribal, or territorial laws, rules, and regulations, including local business and workplace guidance. Click here for the full CDC guidance.

What is herd immunity?

Herd immunity is a term for when a community reaches a certain threshold of people protected from a disease through vaccinations, or because they have already had the virus. This makes it hard for the virus to spread from person to person.

Herd immunity is important for people who cannot be vaccinated — like newborns — because it helps protect them, too. With COVID-19, this is even more crucial since the vaccine is not currently being distributed to those under 16 years old. When more people have developed immunity to a virus, it protects them and others by slowing and eventually stopping the spread.

Herd immunity works differently for every virus. The percentage of the population needed to reach herd immunity for COVID-19 is still unknown.

How can you find out more?

It is normal to have questions about new vaccines. If you have questions or want more information about the COVID-19 vaccines, reach out to your doctor for more information.

Find a vaccine location near you in Massachusetts at

*CDC and the U.S. Food and Drug Administration (FDA) recommend use of Johnson & Johnson’s Janssen (J&J/Janssen) COVID-19 Vaccine resume in the United States, after a temporary pause.