Comparison of COVID-19 Variants of Concern: Is Omicron Less Severe?

Among patients in South Africa who contracted SARS-CoV-2 infection during the wave dominated by the Omicron (B.1.1529) variant, fewer required hospitalization, supplemental oxygen, or transfer to an intensive care unit (ICU) compared with previous waves, according to a research letter published in JAMA.

On November 24, 2021, a fourth wave of COVID-19 infections in South Africa was attributed to the Omicron variant. This variant of concern was found to have a high number of spike protein mutations, raising concerns that it may evade protection from COVID-19 vaccination and increase the risk for transmission.

To assess the outcomes of the SARS-CoV-2 Omicron variant, researchers from Netcare Ltd South Africa, a private health care group comprising 49 acute care hospitals (>10,000 beds), retrospectively reviewed patient data. The researchers sought to compare COVID-19 outcomes that occurred during the Omicron wave with those that occurred during waves of prior SARS-CoV-2 variants, including the ancestral, Beta, and Delta variants. To compare outcomes, the researchers identified the period in which SARS-CoV-2 positivity rates reached 26% in previous waves. Periods assessed included waves dominated by the ancestral (June 14-July 6, 2020), Beta (December 1-23, 2020), Delta (June 1-23, 2021), and Omicron (November 15-December 7, 2021) variants.

Compared with waves of the ancestral, Beta, and Delta variants, the number of patients who received hospital treatment was decreased during the Omicron wave (n=2351 vs 3875, 4632, and 6342). In addition, the researchers noted that the proportion of patients who required hospitalization during the Omicron wave was also decreased compared with waves of the ancestral, Beta, and Delta variants (41.3% vs 67.8%, 69.0%, and 69.3%, respectively; P <.001).

Further analysis showed that patients hospitalized with COVID-19 during the Omicron wave were younger, more were women, fewer had comorbidities, and fewer presented with acute respiratory illness compared with those hospitalized during the previous 3 waves (all P <.001).

The researchers assessed outcomes among patients who contracted COVID-19 infection during each of the 4 waves. Among patients who contracted COVID-19 during the ancestral, Beta, Delta, and Omicron waves, 17.6%, 80.3%, 82.0%, and 74.0% received supplemental oxygen; 1.6%, 16.4%, 8.0%, and 12.4% required mechanical ventilation; 18.5%, 42%, 36.6%, and 29.9% were admitted to the ICU; 2.7%, 19.7%, 25.5%, and 29.1% died; and the median length of hospitalization was 3.0, 8.0, 7.8, and 7 days, respectively (all P <.001).

The researchers noted that COVID-19 vaccines were not available during the ancestral, Beta, and Delta waves. Among patients hospitalized with COVID-19 infection during the Omicron wave, 66.4% were unvaccinated and 24.2% were vaccinated.

This study was limited by the lack of SARS-CoV-2 virus genotyping and the inability to differentiate patients hospitalized with COVID-19 from asymptomatic patients who were hospitalized for other diagnoses with an incidental positive test result. In addition, at the time of publication, 7% of patients infected with COVID-19 during the Omicron wave remained hospitalized.

The researchers concluded that “further research is needed to determine if the differences between waves are affected by preexisting acquired or natural immunity or if Omicron may be less pathogenic than previous variants.”

Reference

Maslo C, Friedland R, Toubkin M, Laubscher A, Akaloo T, Kama B. Characteristics and outcomes of hospitalized patients in south africa during the COVID-19 omicron wave compared with previous waves. JAMA. 2021;e2124868. doi:10.1001/jama.2021.24868