How severe is Omicron infection?

Less than 4 weeks after the announcement Coronavirus mutant containing a mutation Found in southern Africa. Since then, dozens of countries around the world have reported cases of Omicron. Anxious number of infections Those who have been vaccinated or have previously had a SARS-CoV-2 infection.

But political leaders and public health officials are trying to set their course through the looming surge of Omicron, so they must do so without a solid answer to important questions.

So far, the data is lacking and incomplete. “There is an inevitable delay between infection and hospitalization,” says Mark Woolhouse, an infectious disease epidemiologist at the University of Edinburgh in the United Kingdom. “In the meantime, you have to make policy decisions, which is not easy.”

Hospitalization rate

Early results suggest a faint light of hope. Reports from South Africa consistently show lower hospitalization rates as a result of Omicron infections compared to infections caused by the delta mutation, which is currently responsible for most SARS-CoV-2 infections worldwide. I’m pointing out. On December 14, Johannesburg’s South African private health insurance company, Discovery Health, announced that people infected with Omicron had a 29% lower risk of hospitalization than those infected with previous variants.

This fuels the suggestion that Omicron causes milder illnesses than previous variants. However, researchers say it is too early to confirm and details of the main methodologies of the study have not yet been published. Such details include data on the severity of the disease, which can be confused by factors such as hospital capacity, age and overall health of the first infected person, and degree of previous exposure to the coronavirus. It is important when interpreting.

However, Discovery Health results are consistent with other studies in the country, says Waasila Jassat, a clinician and public health expert at the National Institute of Infectious Diseases in Johannesburg. “There are many warnings and disclaimers in the initial severity data,” she says. “But the situation is very consistent.”

It will take some time before a consistent situation becomes apparent from countries that are currently low in Omicron infection. On December 13, Denmark released data showing that the hospitalization rates of people infected with Omicron appear to be comparable to those of people infected with other variants. However, this comparison was based only on about 3,400 cases of Omicron infection and 37 hospitalizations.

Similarly, December 16th report No evidence of reduced hospitalization due to Omicron infection was found from Imperial College London compared to Delta in the United Kingdom, but this was also based on a relatively small number of cases. Troels Lillebæk, an infectious disease specialist at the University of Copenhagen, as a whole, the numbers are still too small to make a firm conclusion about the severity of the disease caused by Omicron.

Also, rapidly spreading variants can put a dangerous burden on the medical system, even if the risk of serious illness or death is relatively low for any individual. “A small percentage of the very large numbers are still large,” says Woolhouse. “Therefore, population-level threats are very real.”

South African optimistic data may not indicate that Omicron itself is benign over previous variants. More than 70% of the population in areas heavily infected with Omicron have previously been exposed to SARS-CoV-2, and about 40% have been vaccinated with the COVID-19 vaccine at least once, Jassat said. .. This makes it difficult to unravel the effects of existing immunity from the inherent properties of the variant itself.

Vaccine protection

In the laboratory, Omicron It may be possible to avoid immunity with the COVID vaccine, And early data from the UK Health and Security Agency suggest that the vaccine is not as defensive against Omicron infection as it is against other variants, although the number of cases studied was too small. , See how much your defense has been reduced.

Nevertheless, the vaccine can continue to protect many recipients from the serious illness and death of COVID-19.In addition to antibodies, the immune system of previously infected and vaccinated people recognizes fragments of viral proteins and deploys cells called T cells that can destroy virus-infected cells. Limit the scope of infection..

Researchers mapped the entire Omicron mutation to a menu of SARS-CoV-2 protein fragments recognized by T cells after spontaneous infection and vaccination, but found no mutations in most of these fragments. .. According to Alessandro Sette, an immunoscientist at the La Jolla Institute for Immunology in California, over 70% of fragments are completely intact when vaccinated.

There is still a lot to do. Scientists have already conducted laboratory assays to determine how well T cells produced in response to vaccines and other mutant infections respond to Omicron, with results in the coming weeks. Expected. “We are optimistic that responsiveness will be maintained, at least in part,” says Sette. “I still don’t know how much it will be saved.”

At this time, there is no direct way to draw a line between the degree of T cell reactivity and protection against serious disease. Previous studies have shown that a strong T-cell response to SARS-CoV-2 correlates with reduced viral load and less severe disease, but its defenses may begin to decline. A threshold has not been established. Eventually, you’ll have to wait for data on hospitalization and death by Omicron.

Infectious diseases in children

As these data become apparent, researchers will pay particular attention to the effects of omicon on children. South African results suggest that hospitalization rates for children infected with Omicron are higher than seen in previous waves. However, researchers warn that this does not necessarily mean that children are more vulnerable to Omicron than Delta and other varieties. Jassat states that children have a lower rate of pre-coronavirus infection and vaccination than adults. That is, the level of existing immunity is not very high.

The high hospitalization rate of children in the early stages of the outbreak may reflect the high capacity of the hospital, otherwise to observe children who may be sent home. She adds that she gives the luxury to keep in.

David Daudi, an infectious disease epidemiologist at Johns Hopkins, can also affect the circumstances in which children are exposed. Bloomberg Public Health School in Baltimore, Maryland. “Everyone here focuses on pathogens,” he says. “But it’s not just about variants, it’s about hosts and environments.”

This article has been duplicated with permission First edition December 17, 2021..