By Stan Deresinski, MD, FACP, FIDSA
Clinical Professor of Medicine, Stanford University
SYNOPSIS: While vaccination provides protection against infection with the BA.1 Omicron variant of SARS-CoV-2, high level protection from a need for hospitalization requires receipt of a booster dose.
SOURCE: Danza P, Koo TH, Haddix M, et al. SARS-CoV-2 infection and hospitalization among adults aged ≥ 18 years, by vaccination status, before and during SARS-CoV-2 B.1.1.529 (Omicron) variant predominance — Los Angeles County, California, November 7, 2021-January 8, 2022. MMWR Morb Mortal Wkly Rep 2022;71:177-181.
Danza and colleagues addressed the relative efficacy of COVID-19 vaccination during the shift in the United States from a predominance of infection with the Delta variant to the Omicron variant. They examined the cases, hospitalizations, and deaths in adults in Los Angeles County during the period from Nov. 7, 2021, to Jan. 8, 2022, a time that encompassed the last weeks of Delta predominance, which ended on December 11.
During the period examined, the number of cases increased, and this increase accelerated with the emergence of Omicron dominance — an occurrence that was most dramatic in individuals who had not been both vaccinated and received a booster. Thus, during the “time of Omicron,” the incidence of infection was 2.0 times higher in the unvaccinated than in those vaccinated but not boosted, and it was 3.6 times higher than in those who had been boosted. Vaccination, particularly with boosting, provided good protection against infection and dramatically better protection against hospitalization. Thus, lack of vaccination was associated with a 5.3 times greater risk of hospital admission when compared to the vaccinated, while the incidence of hospitalization was an astounding 23.0 times higher in the non-vaccinated than in the vaccinated and boosted group.
COMMENTARY
The evidence seems clear that the Omicron variant is more transmissible than previous variants, including Delta. At the same time, it appears to cause less severe disease than Delta (although this assessment is, to some extent, confounded by the frequent presence of partial immunity conferred by prior infection or vaccination). Some ex vivo evidence suggests that these observations may be related to greater infectivity of upper airways and lesser infection of lung tissue.
One question is — what’s next? The Omicron variant widespread in the United States has been designated BA.1. A subvariant designated BA.2 has appeared in dozens of countries (with a few cases so far detected in the United States) and this has been reported to be 1.5 times more transmissible than BA.1. How will it affect the current circumstance?
The data reviewed by Centers for Disease Control and Prevention demonstrates that vaccination produces relatively modest protection against infection and hospitalization due to COVID-19, but if you want a high degree of protection sufficient to prevent hospitalization, boosting is necessary. What degree of protection is provided against the BA.2 subvariant of Omicron remains unknown. The same question can be asked of the Omicron-specific vaccines under study.
While vaccination provides protection against the omicron variant of SARS-CoV-2, high-level protection from a need for hospitalization requires receipt of a booster dose.
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