Booster doses of mRNA vaccines provided strong protection against hospitalization and death from COVID-19 in Qatar, though breakthrough SARS-CoV-2 infections were greater for the omicron variant compared with the delta variant, according to a study by investigators at Weill Cornell Medicine—Qatar.

Dr. Laith Abu-Raddad, director of the WHO Collaborating Center for Disease Epidemiology Analytics on HIV/AIDS, Sexually Transmitted Infections, and Viral Hepatitis at Weill Cornell Medicine—Qatar, and his colleagues published their results on March 9 in the New England Journal of Medicine.

The team conducted a retrospective matched cohort study to determine the effectiveness of booster vaccination compared with two doses of vaccine during a large wave of omicron infection in Qatar from mid-December 2021 through January 2022. The booster dose reduced the risk of symptomatic omicron infections by about 50 percent compared with people who received only two doses of the Pfizer-BioNTech COVID-19 vaccine. Booster doses also increased protection against hospitalization and death during omicron infections by almost 80 percent compared with two Pfizer-BioNTech vaccine doses. The study documented nearly identical levels of protection among people who received the Moderna COVID-19 vaccine and booster.

Those who get booster doses are substantially more protected."

Dr. Laith Abu-Raddad, professor of population health sciences, Weill Cornell Medicine

Dr. Abu-Raddad and his team took advantage of recently established advanced digital health platforms in Qatar to analyze national health system data on about 2.2 million people vaccinated against SARS-CoV-2. They compared SARS-CoV-2 infection and COVID-19 hospitalization rates in about 189,000 people who received two doses of the Pfizer-BioNTech vaccine with an age-, sex- and nationality-matched group of about 189,000 people who received two doses plus a booster. They also compared infection and hospitalization rates in about 67,000 people who received two doses of the Moderna vaccine and a matched set of 67,000 who got the booster.

While the booster doses continued to provide strong protection against serious illness, Dr. Abu-Raddad and his team found that they offered less protection against becoming infected with the omicron strain than with previous strains. They noted that booster doses of the Pfizer-BioNTech vaccine were 85 percent effective at preventing symptomatic infections with the delta strain of SARS-CoV-2, compared with about 50 percent effectiveness against omicron.

"We have really good vaccines that work very well against COVID-19 hospitalization and death, but they are no longer working as well against symptomatic infections," Dr. Abu-Raddad said.

Dr. Abu-Raddad and his team are now using Qatar's health system data to study vaccine protection against a new strain of omicron (BA.2) that appears to be even more infectious. This strain is rapidly becoming the dominant strain worldwide. So far, it does not appear to cause more severe disease than the original omicron strain. They also have preliminary evidence that people who were infected with the original omicron strain are about 95 percent protected from infection with the new variant. Another study suggests that while vaccine protection wanes quickly, natural immunity after infection with SARS-CoV-2 persists, providing about 50 percent protection against a new infection.

For now, Dr. Abu-Raddad said booster shots are the best way individuals can protect themselves against current and future strains of SARS-CoV-2. But to prevent further pandemic-related disruptions, he said it would be essential to develop even better vaccines.

"In the future, we need a new generation of vaccines that protect against both infection and severe disease and that are effective against a broad range of variants," he said. "We can't keep playing catch up with the virus."