MRNA vaccines blocked worst outcomes as variants spread, U.S. says

Messenger RNA vaccines were highly effective at preventing people from suffering the most severe outcomes from COVID-19 even as infectious new coronavirus variants spread, a U.S. study found.

Receiving two or three doses of a vaccine made by either Moderna Inc. or partners Pfizer Inc. and BioNTech SE led to a 90% reduction in the risk of needing to be put on a ventilator or death because of COVID-19, according to a study published by the Centers for Disease Control and Prevention on Friday.

Both the Pfizer and Moderna shots are approved by federal regulators as an initial two-shot primary series for most people. Regulators have cleared third-dose booster shots on an emergency basis, and the drugmakers have asked that clearance for additional doses be considered. Those who support the idea of more booster shots cite the potential for a new variant to cause another wave of widespread infections.

The CDC study looked at data gathered from March 2021 to this January, periods when the alpha, delta and omicron variants were circulating in the U.S. In recent months, when the omicron variant was dominant, three doses of an mRNA shot provided 94% protection against the worst outcomes. Researchers compared vaccinated and unvaccinated adults hospitalized with COVID-19 in 21 medical centers across 18 states.

The findings come as the U.S. has shifted away from an emergency response to the pandemic as cases caused by omicron ebb. However, as many states move to get rid of pandemic-curbing restrictions, there is concern that cases could again rise.

The new data showing that three mRNA doses provide strong protection against severe omicron disease are also likely to raise questions over whether fourth vaccine doses are needed at this point. This week, both Pfizer and Moderna asked the Food and Drug Administration to clear fourth doses.

In a separate study, also published Friday in the CDC’s Morbidity & Mortality Weekly Report, researchers found that in January, unvaccinated adults were 12 times as likely to be hospitalized compared with adults who had received a booster or additional dose. Adults who were vaccinated but hadn’t received a booster or additional dose were three times as likely to be hospitalized.