How will we know when a COVID-19 booster shot will be needed?


A: When immunity starts waning and/or breakthrough infections start increasing in vaccinated people, boosters will likely start to be recommended.

The exact length of time that the currently available COVID-19 vaccines will provide immunity for is not currently known. Researchers are, however, continuing to monitor people who took part in vaccine trials to try to determine this. So far, studies have shown that protection remains robust for AT LEAST 6 months for the Pfizer and Moderna vaccines (and most likely this will be true for at least one year). See our recent post about the Pfizer vaccine after 6 months.

Studies are also ongoing which are monitoring decreases in antibody levels as well as other immune components over time among those who were vaccinated.

The CEO of Pfizer said last week that while protection was still high at 6 months, he thinks there will be a need for a booster to be administered between 6-12 months and then possibly each year, based on available data (which hasn’t been released). It has been suggested that if efficacy of the currently available vaccines drops below 50%, this might be one indication that we need to deploy booster vaccines as this was the threshold that had to be met in the original trials. When more information becomes available on the extent to which immunity decreases over time and how this relates to the need for boosters, we will provide updates!!

Another sign we can look for that may indicate the current vaccines are becoming less effective against circulating variants of the SARS-CoV-2 virus are increases in breakthrough infections (i.e., infections among those who have been vaccinated)-especially those that result in severe illness, hospitalization or death. This information is being tracked by the United States (U.S.) Centers for Disease Control who recently reported that only 5800 individuals out of over 75 million who have been vaccinated in the U.S. have become infected with SARS-CoV-2. Look out for a post specifically on what we know so far about breakthrough infections this week!

In case we need them, companies are currently testing several strategies for booster vaccinations: 1. Giving people an additional dose of the original vaccine, 2. giving people a booster shot that is formulated specifically to a new variant or 3. giving people a booster shot that targets several variants of the SARS-CoV-2 virus at once. To learn more about these strategies, see our prior post. The CEO of Moderna recently said that they hope to have a booster vaccine available by Fall. Several other companies are also testing boosters-so we should have options when and if we need them.

And in case you are wondering, yes, people will most likely be able to mix and match original and booster vaccine types. This may even be beneficial due to something known as a “heterologous prime boost” whereby different vaccines stimulate an immune response in slightly different ways, creating a more robust immune response overall! A study in the UK is currently ongoing to evaluate this strategy, so check back for an update on results of this trial!

For now, the vaccines currently available have been shown to be highly effective at preventing hospitalization and death. This is true of vaccines tested during specific periods or in geographic regions where new variants were more dominant. Also, the more people who get vaccinated, the more we can slow down transmission of SARS-CoV-2 and prevent opportunities for further variants to develop. So when it is your turn, don’t hesitate to get vaccinated-*The best vaccine is the one you can get today!*

Overview of when we might need boosters

More information on the Moderna vaccine after six months

More information on breakthrough infections

More information on the UK mix and match trial

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