Covid booster shot reduces hospitalization risk: study

A booster dose of the Covid 19 vaccine reduces the odds of hospitalization from the omicron variant, according to a new study released Friday by the Centers for Disease Control and Prevention.

The vaccine's impact against omicron in the United States is now accounted for more than 99 percent of new cases in the country, according to three new studies from the agency.

The research underscores the importance of booster shots in order to protect against severe illness from the rapidly spreading variant that has overwhelmed hospitals.

"You don't want to be that one person with a bad outcome, that requires hospitalization, when there is no hospital bed for you," said Syra Madad, an infectious disease epidemiologist at the Harvard Belfer Center for Science and International Affairs.

The new studies show that booster shot can provide significant protection against hospitalization or emergency medical care because of Covid-19.

A third dose of either the Pfizer-BioNTech or Moderna vaccine was found to reduce the odds of a hospital or emergency room visit by 94 percent during the delta wave, and by 82 percent when omicron started spreading, in one analysis of 259 hospitals and 383 emergency departments from late August through early January.

The data included adults who had received either the Pfizer or Moderna vaccine. The authors were able to tease out the effects of boosters during the delta and omicron waves of Covid.

When Delta was surging, the two doses of the vaccine were 86 percent effective against visits to emergency departments and urgent care centers for Covid illnesses. After 6 months, the effectiveness fell to 76 percent, but a booster raised the effectiveness to 94 percent.

According to the CDC, less than half of the U.S. population eligible for a booster dose has received one.

The vaccine's effectiveness for keeping people out of ERs and urgent care centers fell dramatically after the second dose, to 38 percent in the US, despite the fact that a booster dose is more important now that omicron accounts for nearly all Covid cases in the U.S. A booster shot raised that level of effectiveness to 82 percent.

Two shots were 81 percent effective when compared to patients who needed to be admitted to the hospital during the omicron surge. That effectiveness fell to 57 percent in people who were 6 months out of their second dose, but then rose to 90 percent after a third dose.

Two additional studies, published Friday by the CDC, indicate that boosters offered significant protection against both infection and symptomatic Covid, though that protection was higher during the delta surge compared with omicron.

One study, published in the Morbidity and Mortality Weekly Report, found that people who received three doses of an mRNA vaccine were more protected against infection, compared to people with only two doses. The study found that this was particularly true for people over the age of 50.

A study published in the Journal of the American Medical Association found that three doses of an mRNA vaccine were more protective against symptomatic Covid than with people who were either unvaccinated or only received two shots.