Corona variants: Omicron is probably not the end

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The Omicron-Covid-19 wave is probably not the end. There are already other variants of this SARS-CoV-2 mutation as well. “We are in a highly dynamic event,” said expert Andreas Bergthaler (MedUni Vienna/Center for Molecular Medicine; CeMM) in an online physician training session on Wednesday evening. In the therapy of Covid-19, most monoclonal antibodies had lost their effect again due to the constant mutation of the pathogens, he said.

“From the beginning of the (SARS-CoV-2) epidemic, we have been constantly surprised. We are now at as many cases (of infection; note) as we have ever had. We have very effective vaccines available. But I know I don’t know (much),” explained Bergthaler, who recently took up a professorship in molecular immunology at MedUni Vienna and has been studying SARS-CoV-2, its spread and mutations since the beginning of the Covid 19 pandemic. It is also completely unclear how much longer the world will have to contend with SARS-CoV-2 in its various variants.

New corona variants keep pandemic going
What’s driving the pandemic are the virus’ constantly emerging new mutations. Says Bergthaler, “The mutations of SARS-CoV-2 occur two to three times slower than in influenza (flu; note).” But due to the extremely short replication time of the pathogens, new mutations are constantly occurring; there is probably a whole “cloud” of minimally different viruses even in the individual Covid-19 patient. The fittest variant could then spread further.

For all the progress, the understanding of what to expect from which viral variant remains poor. The delta variant, which also took proverbial “command” in Austria last year, had been known internationally as of March 2020. In India, the spread would have stagnated for months, as Bergthaler recapped at the Austrian Society for Infectious Diseases and Tropical Medicine (OEGIT) event. Then, suddenly, transmission, with all the consequences, effectively exploded worldwide.

Omicron much milder than Delta
“Crucial are the transmission capacity, the pathogenicity (how strongly it causes disease) and the capacity for ‘immune escape’ (evasion of immune defenses, including vaccination),” the expert explained. Omicron beats the other known virus variants “hands down” in terms of immune escape, he said. “The Omicron variant replicates quite poorly in the Petri dish (laboratory). It’s probably attenuated, but it hops from person to person faster. All in all, the courses are much milder than Delta.” In terms of reproductive number (R0), he said, the original Wuhan virus was at a factor of 2.5 (one infected person infects an average of 2.5 other people). The SARS-CoV-2 alpha variant had a reproductive factor between four and five, and delta and omicron were between five and eight.

“Omicron was pretty darn fast,” Bergthaler said. However, according to California data, illnesses caused by Omicron led to necessary hospital admissions 52 percent less often compared to the Delta variant. The need for intensive care treatment is 74 percent less likely to occur. Mortality is 91 percent lower.

Around two mutations per month
What happens next remains uncertain, according to the expert. “We see about two mutations per month. That’s amazingly constant. You can sort of set your Swiss watch by that.” In Austria, experts now have a “pretty good overview of the epidemiological situation” via wastewater analysis from more than 80 sewage treatment plants and thus 55 percent coverage of the population. For example, new subvariants of Omikron have already been registered.

SARS-CoV-2 as a “moving target” so far regularly beats even the most provisionally efficient therapies. In the past two years, numerous monoclonal antibodies for the earliest possible treatment of high-risk patients have already been approved and entered the market. The antibodies block the infection of cells by the covid-19 pathogens by docking with the spike protein on the surface of the viruses. This reduces the rate of severe disease progression by about 80 percent.

But Omicron escapes most of these drugs. According to infectiologist Florian Thalhammer (MedUni Vienna/AKH), only one monoclonal antibody (sotrovimab) is currently effective for omicron infections. However, new such drugs with better efficacy will soon be available, he said.

In any case, the future surrounding the pandemic is written in the proverbial “stars.” Bergthaler does not necessarily expect “herd immunity” from infecting many people, even with the current wave of Omicron. Each new virus variant would throw humanity back again, he said. According to Thalhammer, there are many patients at the Vienna AKH who have been vaccinated three times or twice and recovered once from SARS-CoV-2 and have now become ill again with Omicron – with a mild course. The case of an unvaccinated hospital employee is also known, who was infected by the original Wuhan SARS-CoV-2 virus, by a pathogen of the delta variant and finally also by Omicron and fell ill.