Omicron hospitalisation risk lower compared to Delta: Studies

Mangalore Today News Network

New Delhi, Dec 23, 2021: The Omicron coronavirus variant could be less likely to cause severe disease and hospitalisation compared to the Delta variant. This belief has been further strengthened by two new preprint papers.

 

A study released online on Wednesday as a working paper by researchers at the University of Edinburgh in the United Kingdom suggested that the highly mutated Omicron is associated with a two-thirds reduction in the risk of Covid-19 hospitalisation when compared to the Delta variant. The research was based out of Scotland, reported CNN.

The other paper suggested that patients infected with Omicron had 80% lower odds of being admitted to the hospital compared to Delta infections. But once a patient was hospitalised, there was no difference in the risk of severe disease, according to that research, based out of South Africa. The paper was posted on Tuesday to the online server medrxiv.org.

Both studies were based on preliminary data and have not yet been published in a peer-reviewed journal.

The Scotland study included data on 23,840 Omicron cases and 1,26,511 Delta cases, from November 1 to December 19. Fifteen people were hospitalised for Omicron infection and 856 hospital admissions were recorded among Delta infections.

"Although small in number, the study is good news. The two thirds reduction in hospitalisation of double vaccinated young people compared to Delta indicates that Omicron will be milder for more people," James Naismith, Director of the Rosalind Franklin Institute and professor of structural biology at the University of Oxford said on Wednesday. He was not involved in either of the studies.

"The study is rigorous but it is early (this might change a bit with more data and more studies will report in the weeks ahead). It should be noted that some South African scientists have been saying Omicron was milder for some time," Naismith said. "Although the two-thirds reduction is significant, Omicron can cause severe illness in the doubly vaccinated. Thus, if Omicron continues to double every few days, it could generate many more hospitalisations than Delta from the double vaccinated population."

The proportion of Omicron cases that were likely to be reinfections in people who have had Covid-19 before, the researchers said, was more than 10 times that of Delta. Their data also showed that having received the third dose of vaccine, or a booster shot, was associated with a 57% reduction in the risk of symptomatic Omicron infection when compared with being at least 25 weeks out from completing a second dose.

"These early national data suggest that Omicron is associated with a two-thirds reduction in the risk of COVID-19 hospitalisation when compared to Delta. Whilst offering the greatest protection against Delta, the third/booster dose of vaccination offers substantial additional protection against the risk of symptomatic COVID-19 for Omicron," the researchers wrote in the paper.

The South Africa paper involved data of 1,61,328 Covid-19 cases reported in the country between October 1 and December 6. The researchers — from the National Institute for Communicable Diseases, University of the Witwatersrand and the University of Cape Town — found that among people with Omicron infection, 2.5% were admitted to the hospital during that time compared with 12.8% of people with Delta infection.

The researchers wrote in their paper, "These are early data and findings may change as the epidemic progresses."

The US’s top pandemic expert and director of the US National Institute of Allergy and Infectious Diseases, Anthony Fauci, presented this latest data from South Africa and Scotland at a White House briefing Wednesday. He added that further research is needed to determine if similar results would emerge in the United States.

"In fact, it appears, that in the context of South Africa, there is a decrease in the severity compared to Delta -- both in the relationship and ratio between hospitalizations and the number of infections, the duration of hospital stay and the need for supplemental oxygen therapy," Fauci said Wednesday.

"Recently, literally yesterday, there was another paper that came out from Scotland, which appears to validate and verify the data that is in South Africa," Fauci said. "This is good news, however, we must wait to see what happens in our own population, which has its own demographic considerations."

A "moderate" reduction in hospitalisation risk from the Omicron variant in England relative to Delta infections was revealed in separate preliminary data from the United Kingdom, according to a report published by the Imperial College Covid-19 response team on Wednesday.

Based on data from all PCR-confirmed SARS-CoV-2 cases in England between December 1 and December 14, the study was conducted by the WHO Collaborating Centre for Infectious Disease Modelling, the MRC Centre for Global Infectious Disease Analysis, Jameel Institute, and Imperial College London. Covid-19 is caused by the SARS-CoV-2 coronavirus.

The study estimates the risk of being hospitalized for a day or longer due to the Omicron variant to be 40% to 45% lower than for the Delta variant.

"We find evidence of a reduction in the risk of hospitalization for Omicron relative to Delta infections, averaging over all cases in the study period," the report states.

"These reductions must be balanced against the larger risk of infection with Omicron, due to the reduction in protection provided by both vaccination and natural infection," the report cautions. "At a population level, large numbers of infections could still lead to large numbers of hospitalizations."

Individuals infected with the Omicron variant after a documented previous infection are 50% to 60% less likely to be hospitalized compared with people with no previous infection, the study says.

The report also says: “The risk of hospitalisation is similar for Omicron and Delta for people who test positive for an infection and who previously received at least two vaccine doses, reflecting reduced vaccine efficacy against Omicron compared with Delta."

"However, the risk of hospitalization in vaccinated people remains significantly lower than for unvaccinated people," adds the report, which has not yet been published in a peer-reviewed journal.

"However, the study suggests there is no reduction in the severity of Omicron compared to Delta for the doubly vaccinated, indicating that it is not milder," Naismith said. "This finding is surprising but is grounded in data. There is no report on the benefit of boosting."