Early data on Omicron shows increase in cases but milder symptoms

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T WEEKS OF WORK After identifying the Omicron variant, hospitals prepare for a covid-19 tsunami. In South Africa, where he has moved Delta, cases are increasing faster than in previous waves. Each person with Omicron can infect 3 to 3.5 more. Delta’s most recent rate in the country was 0.8.

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South Africa is not stranded, which may partly explain the rapid spread of Omicron. However, the earlier variants have benefited from encountering many people without immunity. By now, most South Africans have recovered from covid or have been vaccinated.

In such an environment, Omicron could spread so quickly in two ways. One is greater infectivity, which depends on factors such as the ease with which it enters cells. The other is better immunity escape.

The Delta variant has become dominant mainly due to its transmissibility. In contrast, Omicron appears to have advantages in both areas. Anecdotal evidence of its greatest contagiousness is mounting: wide-spread events after which 35-78% of people who test positive occurred in Norway, Denmark, Spain and Britain.

In addition, Omicron has an unprecedented capacity for reinfection. A recent study by Juliet Pulliam of Stellenbosch University showed that the number of South Africans who tested positive at least 90 days after their last positive test is higher than one would expect based on previous waves. . And the antibodies generated by Pfizer’s vaccine are less effective against Omicron than against previous variants. However, they still achieved solid neutralization in people who received booster shots or previous infections. Current vaccines may offer good protection against serious illnesses caused by Omicron.

The data on virulence are more encouraging. In hospitals, Omicron has yet to show a pattern of worsening disease in the elderly. Among covid-positive hospital patients in the South African city of Tshwane, 70% of people aged 50 to 69 and 90% of those over 80 had severe cases during the Delta Wave. This share is now around 30% for all ages.

The average severity of Omicron cases could increase. If not, one of the possible reasons is that the Omicron mutations lead to milder disease. This would partially offset the impact of an increase in the number of cases, although death rates could rise further if services are overwhelmed. Another explanation is that many older South Africans have received beatings in recent months. If this is the cause, Omicron would pose a serious threat to the unvaccinated. â– 

Sources: NICD, South Africa; Trevor Bedford; “Increased risk of reinfection with SARS-CoV-2 associated with emergence of the Omicron variant in South Africa”, by JRC Pulliam et al. (work document)

This article appeared in the Graphic detail section of the print edition under the title “Mixed signals”


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