As the Delta variant spreads in
In this Q&A, Dr.
Question: In vaccine development, how does a determination get made about a booster schedule?
Answer: A vaccine stimulates the immune system to make a response (antibodies and/or cells) to help fight microorganisms, such as bacteria and viruses, that cause an infection. This response may only last a certain amount of time. How long the response lasts could be determined by following the immune response (for example, the amount of antibody in the blood) or by following people who have been vaccinated for the development of the actual infection. When the protection from the vaccine wears off, a booster vaccine could re-stimulate the immune system to respond again.
Q: How much of the analysis of boosters is being driven by the Delta variant, as opposed to natural changes in immunity conferred by the initial vaccine doses among the general population?
A: Both the Delta variant (which currently accounts for more than 99% of new COVID-19 cases in
Q: What does the early data show about the effectiveness of an additional COVID-19 vaccine shot, particularly in the immunocompromised?
A: Immunocompromised means that the immune system is not working as well as it should. This can be caused by certain diseases such as cancer, autoimmune diseases or HIV, or by taking certain drugs, including cancer chemotherapy, steroids and drugs that affect the immune system, known as immunomodulators. We know from clinical data that immunocompromised people may not respond sufficiently to one or two COVID-19 vaccinations; some early data suggests that some will respond sufficiently with a third COVID-19 vaccination. This was the idea when the
Q: Should vaccinated people who were previously infected with SARS-CoV-2 receive a vaccine dose?
A: Current recommendations are that people with prior COVID-19 infection should receive COVID-19 vaccination. This is because natural COVID-19 infection stimulates variable amounts of immune responses. For example, early data suggested that approximately 10% of people who had COVID-19 did not develop antibodies.
Q: How will scientists gauge the long-term effectiveness of a third COVID-19 vaccination shot?
A: People who enrolled in the original COVID-19 vaccine studies continue to be actively followed, both monitoring their immune responses (their antibody levels, for example) and to see if they acquire COVID-19 infection. Some of the original COVID-19 vaccine studies are testing booster strategies, so we will have more data to help guide clinical decisions.
Q: What's the likelihood that COVID-19 vaccinations will be administered annually, much like the flu shot?
A: The reason that flu vaccinations are given yearly is because the most common circulating flu viruses change each year. For that reason, last year's flu vaccine may not be effective against this year's flu viruses. We don't yet know if that will be the case for COVID-19 vaccinations.
Q: Have any differences been seen in side effects or risks with an additional COVID-19 vaccine shot?
A: We only have limited information on the side effects and risks of a third COVID-19 vaccination. So far, it looks like the side effects are similar to those of the first and second shots (most commonly, injection site pain or redness). More serious side effects appear rare.
Q: Is there any data about the safety and efficacy of mixing COVID-19 vaccines (i.e. two doses from
A: Currently, the
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