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- People who have immunocompromising conditions are recommended to get a third dose of mRNA vaccines 28 days after the second dose.
- This is considered part of the initial vaccination for them, not a booster.
- A new report from the CDC finds that a third dose reduces risk of hospitalization for both immunocompromised and immunocompetent patients.
In a new study released by the Centers for Disease Control and Prevention (CDC), researchers analyze hospitalization data for people over the age of 18 with and without immunocompromising conditions. They compared people who had a third dose of an mRNA vaccine, from either Pfizer/BioNTech or Moderna, and people who did not.
The data are from 21 hospitals in 18 states during the period of August to mid-December 2021. The researchers wanted to evaluate the effectiveness of a third shot of a vaccine, especially since a third shot was approved as part of the primary series for immunocompromised people four weeks after their second dose. This means that the third dose is a necessary part of initial vaccination, and not considered a “booster.”
They found that vaccine effectiveness at preventing hospitalization was higher for people who received a third dose. This was true for both groups of people who received it as part of the initial series because they were immunocompromised, or if they received it as a booster dose.
The study included nearly 3,000 people with a median age of 62 years old. For people without immunocompromising conditions, a third dose increased vaccine effectiveness against hospitalizations from 82 to 97 percent. For people who are immunocompromised, a third dose increased effectiveness from 69 to 88 percent.
This analysis didn’t look at how new variants may affect vaccine effectiveness, especially for omicron which emerged in late 2021. The scientists also are unsure about the potential for a fourth dose as a booster for immunocompromised individuals, although health officials in Israel are exploring that possibility.
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