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UF Health expert discusses COVID-19 booster shots

As the delta variant of the coronavirus persists, federal officials are urgently studying the safety and effectiveness of a third dose of COVID-19 mRNA vaccines as well as a second shot of the Johnson & Johnson vaccine. If the Food and Drug Administration and a Centers for Disease Control and Prevention advisory committee agree to proceed, shots could be flowing into arms sometime this fall.

Michael Lauzardo, M.D., deputy director of UF’s Emerging Pathogens Institute and an associate professor in the UF College of Medicine’s department of medicine, talks about issues related to the third vaccine dose.

Question: What are vaccine booster shots?

Answer: For many vaccines, the immunity prompted by the vaccine wanes over time. This is a fairly common phenomenon, seen with multiple vaccines that are administered routinely here in the United States. The recommended time between booster shots can vary widely, depending on the disease for which the vaccine is administered and the way the vaccine is made. For example, healthy adults are advised to get a booster shot for tetanus and diphtheria once every 10 years.

There are data starting to appear that immunity to COVID-19 produced by the currently available vaccines begins to wane six to eight months after a person was initially vaccinated. This is not totally unexpected. Immunity to other coronavirus infections, such as those linked to the common cold, has long been known to decrease over time. That is one reason why people get colds year after year. It should be emphasized that people who have received one of the COVID vaccines still have very effective protection against serious infections, hospitalizations and death. However, the risk of mild infections does appear to increase over time.

Q: How does this differ from getting a “third shot” as part of an initial immunization series?

A: Some vaccines require as many as three initial shots to provide protection against a disease. For instance, it is recommended that babies get a series of three tetanus/diphtheria/whooping cough shots to provide good protection against infection. For certain individuals, particularly those who are immunosuppressed or at high risk for infection, there have been suggestions that an initial three-shot COVID-19 vaccine series may be advisable. However, there are still not clear recommendations as to when or if this initial third shot is needed.

Q: If a COVID-19 booster shot is recommended, would it be identical to the original vaccine shot that was administered?

A: As of today, yes. The same dose containing the same ingredients or formulation is present in all the vaccines made by each manufacturer. Currently available COVID-19 vaccines continue to provide very high levels of protection against serious infections, hospitalization and death caused by the delta variant. However, protection of the currently available vaccines is not quite as good against infection with the delta variant as it was against infection with some of the earlier strains of coronavirus. For this reason, drug companies are looking at the possibility of modifying the current vaccines so they are better targeted against the delta variant and other new variants that may appear.

If these new boosters are approved by the FDA, their use should provide better protection against COVID-19 variants. It is also possible that recommendations regarding boosters will include recommendations that the dosage be modified, particularly if studies show that a booster given at a lower does will elicit a good immune response with fewer side effects.

Q: So, should I get a COVID booster shot?

A: The COVID-19 vaccines authorized in the United States continue to be highly effective in reducing risk of severe disease, hospitalization and death, even against the widely circulating delta variant. However, it is likely that at some point this fall a booster shot for COVID-19 will be recommended by

CDC, based on concerns about immunity waning over time. And, yes: If CDC recommends a booster shot for waning immunity, getting it would decrease the likelihood that you would get an infection with the COVID-19 virus.

There are already recommendations that people who are immunosuppressed or at high risk for COVID-19 infections get a third shot. In many ways, this can be regarded as being equivalent to getting a third shot as part of the overall immunization series, for people who may not have gotten an optimal immune response to the initial immunizations due to their health status. If you are in this category, an additional immunization is advised.

Q: If I received the Johnson & Johnson vaccine, will I need a booster shot?

A: People who received the Johnson & Johnson vaccine will likely need a booster shot but recommendations from the CDC and the FDA for people who received that vaccine are still being finalized. Officials are awaiting more data to help make the final decisions and recommendations. It is likely that another dose of the Johnson & Johnson vaccine will be recommended due to some promising data that came out in late August showing a strong response to a second Johnson & Johnson vaccine. It is a little less clear if a second dose of an mRNA vaccine (Moderna or Pfizer) will be recommended as an option. Again, we are waiting for the data to be final but initial reports have been promising.

Q: If I was vaccinated more than eight months ago, will the booster shot still be effective?

A: It is important to remember that, as best we know, the initial vaccine series are still highly effective without the booster. But, as stated earlier, the strength of that immunity may wane over time and the booster will make it even more effective — especially to prevent mild to moderate illness. There is no “outer limit” after the initial dose that a booster can still be effective. Once the recommendations are out, we will provide more guidance. Additional doses and boosters will be most important for those most likely to have either a weak initial response or waning immunity.

Media contact: Ken Garcia at or 352-265-9408.

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Doug Bennett
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