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In view of the new Sars-CoV-2 variant, three questions are currently burning: How contagious is omicron? And how good is the immune protection of the vaccinated and recovered? Does the new variant cause more severe disease than Delta? A good month after the first reports, there are already some answers, from South Africa as well as from European countries.
How fast is Omicron spreading?
Still rapidly. In South Africa, by the beginning of December, Omicron had marginalized the previously dominant Delta variant within two weeks. In Denmark and the UK, there are now more new infections with Omicron than with the Delta variant. This is reported by the national authorities.
In both countries, record numbers of new infections were reported before Christmas. In Denmark, there were more than 13,000 per day, and in the United Kingdom, almost 120,000.
In many countries, new Omicron infections have been doubling every two to three days. In many places, Omicron has been driving the number of new infections steeply upwards again for several days, for example in the USA or France – there especially in Paris. Even in countries with a very high vaccination rate, such as Portugal and Spain, the incidences are rising.
In Switzerland, too, more than half of new infections are now caused by the omicron variant, according to the Federal Office of Public Health (as of Dec. 27, 2021). In Germany, delta still dominates, according to figures from the Robert Koch Institute. But here, too, Omicron is expected to take the reins by mid-January at the latest.
How contagious is Omicron?
It could be that Omicron per se is somewhat more contagious than the Delta variant. This is because the risk of contracting the disease in the household from an infected flatmate is 3 times higher with the Omicron variant than with the Delta variant. This is according to the British report mentioned above. The risk of catching the virus from an infected contact person in everyday life is twice as high with Omicron as with Delta.
Cell culture studies by a Hong Kong research group provide an explanation as to why Omicron spreads so quickly. In the experiments, omicron viruses replicated 70 times faster in bronchial cells than delta viruses. Thus, in a person infected with the omicron variant, more new virus particles are present in a shorter time than before, which is sufficient to infect many people.
A second important advantage that the Omicron viruses have over the Delta viruses is the fact that the new variant can largely escape the immune protection of both vaccinated and recovered persons.
To what extent can Omicron escape immune protection?
Significantly better than all other previous virus variants. This is suggested by various studies from South Africa, Germany and the UK. Because of the many mutations of Omicron, this so-called immune escape had already been predicted by experts shortly after the new variant became known.
Cell culture experiments with sera from vaccinated individuals have shown that the antibodies circulating in the blood can hardly neutralize the Omicron virus after two vaccinations. Specifically, the effectiveness has decreased by a factor of 20 to 40. This means that a person needs 20 to 40 times as many antibodies to eliminate invading Omicron virus.
The longer ago the vaccination, the worse the neutralization efficiency. However, the amount of neutralizing antibodies is significantly increased by booster vaccination. Therefore, vaccine manufacturers Biontech and Pfizer advise administering the third spike as early as three months after the second vaccination, given the Omicron wave that is building up.
According to U.K. data, vaccine effectiveness against Omicron is 70 to 75 percent in the first few weeks after the booster. This is worse than against Delta, but still good.
It is unclear how long this booster protection lasts. Apparently, the antibodies survive only several weeks even after a third vaccination. This is because the team led by Frankfurt virologist Sandra Ciesek has shown that already three months after the booster, the efficiency of neutralization has decreased in cell culture studies.
Immune protection against omicron has also declined in recovered individuals. This has been observed not only in South Africa. Currently, experts assume that a survived infection protects 3 to 8 times less well against reinfection with omicron than against reinfection with delta.
However, the protection of both vaccinated and recovered persons against severe covid-19 disease is significantly better than against infection. New data from the UK and South Africa show that vaccine efficacy is about 70 percent even after “only” two doses of the Biontech/Pfizer mRNA vaccine compared to severe disease after infection with Omicron.
How dangerous is omicron?
Here’s some good news: According to initial findings, the new viral variant may be less pathogenic overall, meaning it causes less severe disease than the delta variant.
“The risk of hospitalization for Omicron-infected adults is 29 percent lower than for infections during the first Corona wave,” South African researchers report. And if Omicron patients did need to go to the hospital, they would have a lower risk of being transferred to the intensive care unit. In the current corona wave, there are significantly fewer deaths than before.
However, there is a 20 percent increase in hospital admissions of children in the age group up to five years, he said. But first, most cases are mild. Secondly, the absolute risk of a severe course of disease in children is so low anyway that even this observed increase does not pose a danger to the vast majority of young patients, emphasize the researchers from South Africa.
A few days ago, British researchers from Imperial College in London also found a similar reduction in risk on average across the entire population. However, the scientists emphasize that these statements are only valid at the present time of the pandemic. Because at present in Great Britain above all humans between 20 and 39 years are concerned by Omicron infections. And in this age group, there is in any case much less severe covid-19 disease than among older people. In addition, it is unclear how omicron infection progresses in the unvaccinated.
There is also already a molecular biological explanation for the reduced risk. A team from Cambridge and Japan has observed in cell culture studies that omicron viruses cannot fuse with lung cells as efficiently as delta viruses. As a result, lung cells are no longer as easily invaded by omicron viruses. Lung cell invasion is one of the causes of severe covid-19 disease.
Apparently, some of the mutations in the spine protein, which Omicron had but Delta did not, made fusion more difficult, the authors write in their paper, which has not yet been peer-reviewed. The Hong Kong team of scientists also found evidence that Omicron has difficulty entering lung cells. Delta viruses, for example, were able to replicate 10 times faster in lung cells than omicron viruses.
But even if omicron viruses cause much milder courses than delta viruses, for example, the breathtakingly rapid spread of the new variant alone could cause major problems for health systems, scientists and authorities alike warn. If a large number of people become infected with Omicron in a short period of time, many vulnerable people will also be affected, and they will have a higher risk of a severe course of the disease.
- source: nzz.ch/picture: pixabay.com
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