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A previous SARS-CoV-2 infection protects against Omicron reinfection only 56 percent of the time, researchers found in a review of national data in Qatar.
The immune response to COVID-19 helps protect against reinfection, but that protection is weaker against Omicron than it was against earlier variants of the coronavirus, according to new data.
Having had COVID-19 was 90.2 percent effective against reinfection with the Alpha variant, 85.7 percent effective against a Beta variant reinfection, and 92 percent effective against Delta reinfection, researchers reported on Wednesday in The New England Journal of Medicine.
The efficacy of the vaccines also declines in face of Omicron. Protection provided by booster shots of the mRNA vaccines from Moderna Inc. or Pfizer Inc. and partner BioNTech SE starts waning quickly, according to data published in Friday's Morbidity and Mortality Weekly Report from the U.S. Centers for Disease Control and Prevention (CDC).
Researchers reported that within two months after the second dose of an mRNA vaccine during the surge in infections caused by the Delta variant of the virus, vaccine efficacy was 94 percent against hospitalization and 92 percent against emergency department or urgent care visits.
Efficacy waned thereafter, but climbed to 96 percent and 97 percent, respectively, at two months after a booster shot.
Four months later, however, that protection had declined to 76 percent and 89 percent.
Once Omicron became predominant, vaccine efficacy was 71 percent against hospitalization and 69 percent against urgent care visits within two months after the second dose, 91 percent and 87 percent at two months after a booster, and 78 percent and 66 percent four months later.
The estimates are drawn from analyses of 241,204 COVID-related urgent care visits and 93,408 hospitalizations between August and January.
"Our findings suggest that additional doses [of vaccines] may be necessary," Brian Dixon of the Regenstrief Institute and Indiana University said in a statement. "We also found that people who are Hispanic or Black are half as likely to have a third vaccine dose than people who are white, making [them] more vulnerable to severe COVID-19."
(Reuters)
