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Omicron BA.2 subvariant appears to be less severe than other strains

A study yesterday in JAMA Network Open suggests that the SARS-CoV-2 Omicron BA.2 subvariant carries a significantly lower risk of death than that of Delta and the original Omicron strain, B.1.1.529.

Led by researchers at Massachusetts General Hospital and Harvard Medical School, the study involved 102,315 COVID-19 cases in adults and children in New England diagnosed from Mar 3, 2020, to Jun 20, 2022. Average patient age was 44.2 years, 62% were women, 76.4% were White, and 20.3% of the cases were Delta, 51.4% were Omicron, and 28.3% were BA.2.

Amid Delta, 48.5% of patients had received a primary COVID-19 vaccine series, and 44.7% were unvaccinated, while during Omicron predominance, 65.9% had received a booster dose. Also, fewer people had previous infections during the Delta wave (1.8%) than in the Omicron (6.4%) and BA.2 (5.3%) surges.

COVID-19 30-day death rates were 0.7% for Delta, 0.4% for Omicron, and 0.3% for Omicron BA.2. The adjusted odds ratio (aOR) of death from Delta relative to BA.2 was 2.07 (95% confidence interval [CI], 1.04 to 4.10), and for Omicron it was 2.20 (95% CI, 1.56 to 3.11).

The risk of hospitalization with Delta was significantly greater than that of BA.2 (aOR, 3.84; 95% CI, 2.93 to 5.02). Omicron was also more likely to lead to hospitalization than BA.2 (OR, 2.71; 95% CI, 2.42 to 3.02).

Likewise, intensive care unit admission was six times higher with a Delta infection than with BA.2 (OR, 6.12; 95% CI, 2.57 to 14.5), and with Omicron it was triple (OR, 3.06; 95% CI, 2.28 to 4.10). The relative risk of invasive ventilation was more than quadruple and triple, respectively, with Delta (OR, 4.36; 95% CI, 2.56 to 7.41) and Omicron (OR, 3.55; 95% CI, 2.61 to 4.84).

"After having accounted for a variety of confounding factors associated with SARS-CoV-2 outcomes, the Omicron BA.2 subvariant was found to be intrinsically less severe than both the Delta and Omicron variants," the study authors wrote.

[Source: CIDRAP News, University of Minnesota, 25Oct22]

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