The Science Of Mixing COVID-19 Boosters

An early National Institutes of Health study of different booster combos shows an extra dose of any COVID vaccine increases virus-fighting antibodies. The most dramatic response comes from an MRNA booster after a Johnson and Johnson vaccine. People who got the single-dose shot saw a 76-fold jump in antibody levels after getting a Moderna booster, and a 35-fold rise after a Pfizer booster. That's compared to a four-fold increase after a second J&J shot. However, some medical experts are skeptical because these results are early. One unclear detail: what level dose a Moderna booster would look like matched with a different brand. Moderna is asking the FDA for a booster that is half a dose. But the NIH mix-and-match study only looked at full doses, meaning we don't know if a half-dose of Moderna would cause as high of a jump in antibodies. Mixing shots could make it more accessible for people who may otherwise have issues getting the same brand doses, or those who had a bad reaction to their first dose. The FDA is expected to issue emergency authorization for Moderna and J&J boosters this week. The CDC's own advisory panel is slated to make its own recommendations. And CDC Director Dr. Rochelle Walensky is expected to move quickly thereafter, meaning boosters in arms could happen by week's end.