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Challenges in Inferring Intrinsic Severity of the SARS-CoV-2 Omicron Variant
List of authors
- Roby P. Bhattacharyya, M.D., Ph.D.,
- and William P. Hanage, Ph.D.
N Engl J Med 2022; 386:e14
DOI: 10.1056/NEJMp2119682
Active genomic surveillance and transparent communication by South African scientists and public health practitioners recently heralded a new, rapidly circulating SARS-CoV-2 variant, now called omicron.1 Scientists and the public have been closely monitoring the clinical effects of the omicron-variant wave that has rapidly swept through the population in order to estimate the variant’s relative transmissibility, capability for immune evasion, and severity as compared with previous variants. Omicron’s growth advantage over the delta variant has now been documented in multiple locations. Omicron’s rapid spread throughout South Africa has resulted in fewer hospitalizations and deaths per documented case than were seen during previous Covid-19 waves, an observation that some members of a weary public are understandably eager to ascribe to an intrinsic tendency of this variant to cause less severe illness. Even more than for previous variants, however, caution is warranted when it comes to making inferences about omicron’s intrinsic traits, particularly its severity, on the basis of population-level observations.
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Although these studies were conducted in locations with very different case-ascertainment rates, after correcting for underascertainment, each study estimated that omicron was about 75% as likely as delta to cause hospitalization in an unvaccinated person with no history of SARS-CoV-2 infection.2,3 This meaningful but fairly small difference implies that omicron, alpha, and wild-type SARS-CoV-2 have similar intrinsic severity...
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