Boosters Effective Against Reinfection Hospitalization

Carolyn Crist

April 18, 2022

Editor's note: Find the latest COVID-19 news and guidance in Medscape's Coronavirus Resource Center.

COVID-19 vaccines and boosters provide protection against hospitalization after contracting the coronavirus again, according to a new CDC study.

Although a previous infection may provide some immunity, it may wane over time and not keep patients out of the hospital, the researchers found.

"People had good immunity from (the original strain of the virus) after getting COVID the first time, but after going through the Delta period and now the Omicron period, we wanted to see what the public health impact would be," Jackie Gerhart, MD, one of the study authors and vice president of clinical informatics at Epic Research, told USA Today.

The CDC teamed up with Epic Research, a company in Wisconsin that shares data for public health purposes, to determine how effective vaccines and boosters are against hospitalization following a reinfection.

The research team analyzed electronic health records for more than 50,000 COVID-19 patients who were hospitalized during the Delta and Omicron waves more than three months after a previous infection, which typically indicates a reinfection, including 5,000 people who tested positive.

During the Delta wave from June to mid-December 2021, a two-dose vaccine series from Pfizer or Moderna was about 47% effective against hospitalization due to reinfection. A booster dose was more than 57% effective at that time.

During the Omicron wave from mid-December through February, a two-dose series was about 35% effective. However, the booster dose was nearly 68% effective.

The data about the Omicron wave may be particularly relevant now as the BA.2 subvariant sweeps the country, USA Today reported. Last week, BA.2 accounted for more than 85% of new coronavirus cases nationwide, according to the latest CDC data, and more than 90% of cases in northeastern states.

COVID-19 cases have begun increasing again in the U.S., marking a 32% uptick during the past two weeks, according to the data tracker from The New York Times. The country is reporting about 37,000 new cases and 500 deaths per day.

Cases have more than doubled since the beginning of April in Rhode Island and Washington, D.C., the newspaper reported. New case reports have also begun to increase in the Midwest, with Illinois, Michigan and Wisconsin reporting more than a 40% increase in the past two weeks.

As the pandemic continues, more Americans are likely to become reinfected with the coronavirus, USA Today reported. As a result, public health experts are urging people to maintain up-to-date vaccinations and boosters to reduce the risk of hospitalization.

"If you've been previously infected with COVID, you can get improved immunity through a vaccine and booster," Gerhart said. "We have the tools that can help decrease your likelihood of getting reinfected and hospitalized."


CDC: "Effectiveness of COVID-19 mRNA Vaccination in Preventing COVID-19-Associated Hospitalization Among Adults with Previous SARS-CoV-2 Infection — United States, June 2021-February 2022."

USA Today: "Already got COVID? Vaccines, boosters up to 68% effective against hospitalization from reinfection, CDC study shows."

CDC: "COVID Data Tracker: Variant Proportions."

The New York Times: "Coronavirus in the U.S.: Latest Map and Case Count, updated April 15, 2022."


Comments on Medscape are moderated and should be professional in tone and on topic. You must declare any conflicts of interest related to your comments and responses. Please see our Commenting Guide for further information. We reserve the right to remove posts at our sole discretion.