Vaccines take time to work. After getting a COVID-19 vaccine, it takes a while for the immune system to fully respond and provide protection from the virus. For the Moderna and Pfizer COVID-19 vaccines, it takes up to two weeks after the second shot to become appropriately protected.

Continue to mask, practice hand hygiene and physically distance after getting the vaccine. Studies show that the vaccines from Moderna and Pfizer are more than 90% effective. However, a small number of people who get one of the vaccines will not become immune. It is not yet known if people who get a vaccine can carry the coronavirus the causes COVID-19 and pass it along to others. For this reason, everyone should continue to follow precautions such as physical distancing, handwashing and mask wearing.

Vaccines may benefit those who have had COVID-19. Getting vaccinated even if you have had COVID-19 may be beneficial. It is possible to be reinfected with COVID-19 and again be at risk from the severe health impacts associated with the illness.

Most vaccine side effects are mild. Studies have shown that most reported COVID-19 vaccine side effects are mild. They are normal signs that the body is building immune protection. Some side effects may be more intense than others and might affect a person’s ability to continue daily activities normally, but they should go away in one or two days. Side effects are more likely to occur after the second vaccine in the series. They include pain and swelling at the injection site, chills, joint pain, tiredness, headache, muscle pain and fever (a temperature greater than 100.4 degrees Fahrenheit or 38 degrees Celsius).

More information from Johns Hopkins Medicine on what to expect from COVID-19 vaccines is available at https://www.hopkinsmedicine.org/health/conditions-and-diseases/coronavirus/covid-19-vaccine-what-you-need-to-know.

Johns Hopkins Medicine experts are available for interviews.

[Note: this story was updated on Jan. 29, 2021, to correct information about vaccine efficacy.]