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Two vaccines have been approved by the U.S. Food and Drug Administration for emergency use in the fight against COVID-19. Both the Pfizer-BioNTech and Moderna vaccines require two shots in order to achieve the maximum level of protection against the virus.

Both pharmaceutical companies report that their vaccines are about 95% effective in preventing the virus, but that efficacy hinges on receiving two separate doses. A report from the Florida Department of Health indicates that more than 44,000 Floridians are currently overdue for their second dose of the COVID-19 vaccine.

Dr. John Greene

Dr. John Greene, chair of the Infectious Diseases Department at Moffitt Cancer Center

How much protection does each dose provide?
“Within two weeks of receiving the first dose, the body will produce enough immune response to prevent infection 50 to 80%, but closer to 50%,” said  Dr. John Greene, chair of the Infectious Diseases Department at Moffitt Cancer Center. “When you receive the second dose three to four weeks later, you will achieve about 95% protection against the COVID-19 virus about a week after.”

Do I have to get the second dose in a specific timeframe?
Yes. Both vaccines are to be administered in accordance with the FDA’s authorized dosing schedules. The Pfizer-BioNTech vaccine is to be given three weeks (21 days) apart, and the Moderna vaccine is to be given four weeks (28 days) apart.

Can I mix and match vaccine doses?
If you receive one dose of the Pfizer vaccine, is it okay for the second dose to be Moderna – or vice versa? Health officials say no. The FDA released a statement urging health care providers to follow the authorized dosing schedule, with a reminder that mixing and matching vaccines is not advised. Due to lack of sufficient data to evaluate any changes in vaccine administration, following the authorized dosing schedule is the best way to safely receive the level of protection observed in trials.

Haven’t received your vaccine yet? Click here to read more about what to expect or click here for answers to some of the most commonly asked questions.