On November 26, the WHO designated variant B.1.1.529 as ‘Variant of Concern’ (Voc), with the variant name Omicron. Symptoms, vaccine efficacy and third dose, transmissibility: this is what we know about the variant isolated for the first time in samples collected in Botswana and South Africa.
There is consistent evidence that Omicron has greater transmissibility than the Delta variant in countries, we read on the ISS (Higher Institute of Health) website.
Severity of the infection
Data on the clinical severity of patients infected with Omicron were collected week after week: early findings from South Africa, Great Britain and Denmark suggested a reduction in hospitalization risk for Omicron compared to Delta. However, the risk of hospitalization is only one aspect of the severity of the disease. More data from several countries is needed to understand how other indicators, such as oxygen use or mechanical ventilation or mortality, are associated with this variant in severe cases. Assessments of patient admissions, with a reduction in hospitalizations, should take into account the possible effect of immunity from previous infections or vaccines, beyond the less virulent characteristics that are associated with Omicron.
All the variants of Covid-19, as the WHO recalled in recent days, can cause serious illness or death, particularly in the most vulnerable people by age or physical condition, and prevention through vaccination and non-pharmacological protective measures. (distance, hand hygiene, masks where required, remains essential.
Effectiveness of vaccines
Results in Great Britain indicate a significant reduction in vaccine efficacy against symptomatic disease from Omicron compared to that from Delta after two doses of Pfizer or AstraZeneca vaccine. However, a greater efficacy against symptomatic disease emerged two weeks after the booster, comparable or slightly lower than that against Delta. A study not yet peer-reviewed also reports a loss of efficacy in the primary cycle with respect to hospitalization, although to a lesser extent than with symptomatic disease.