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The results of laboratory experiments look very alarming, but it is important to understand that a 40-fold decrease in neutralization efficiency is not equal to a 40-fold decrease in vaccine effectiveness. A person and his immune system are much more complex than cell culture, so directly transfer research results in vitro on people it is impossible. Obviously, such a significant drop in the effectiveness of neutralization will affect the real protection that vaccines give, but in order to evaluate it, it is also necessary to collect epidemiological data.
One of these necessary parameters is the dynamics of the “omicron” propagation. Based on the data on the change in the number of positive tests in South Africa, experts estimate the increase in new cases of B.1.1.529 infection there at 25% per day. And this is more likely an estimate at the lower limit, since the share of positive tests from all those done is also growing and has already exceeded 26%. The higher this indicator, the more infected we miss: when tracking systems are well established, it is at the level of a few percent.
But even an increase of 25% per day is comparable to the numbers that we saw in the first wave, when the coronavirus began to invade a population that was completely non-immune to it. Such agility of the omicron can be partly explained by its ability to escape antibodies: from the point of view of the immune system of those vaccinated or recovered, its spike protein is a kind of new formation against which there are no antibodies in the body. On the other hand, it cannot be ruled out that the omicron itself is more infectious than the delta, but in order to find out this, it is necessary to compare the rate of spread of two strains in a non-immune population, which we cannot do for objective reasons.
Another way to assess infectiousness requires contact tracing statistics. In Africa, it is poorly established, in Europe after the summer recession, too, but health systems are still much better at solving this kind of problem. And in a couple of weeks since the spread of the virus outside Africa, we have already seen at least one episode of super-spread: in Oslo, at a Christmas dinner, more than 70% of a hundred guests became infected from one person… Another potential spread happened in Sydney: at the end of a party on a cruise yacht, where only the vaccinated or ill were allowed, at least 5 out of 140 guests became infected with omicron. The rest are still in quarantine, so it is possible that the number of confirmed infections will eventually turn out to be higher.
It is also possible to indirectly estimate the intrinsic infectivity of B.1.1.529 in experiments on infecting animals, but it will take time to carry out and analyze the results of such experiments.
Be that as it may, today we see that the “omicron” is not much inferior to the “delta” in terms of propagation speed (although statistics are still scarce, all conclusions must be drawn with caution). And now the main question is related to the course of the disease caused by this strain. Avoiding antibodies does not mean vaccines will do much worse at preventing severe disease. Antibodies are only the first bastion of immune defense, their role is to prevent cell infection. But if it has already happened, T cells come into play, whose task is to destroy everything that is infected. Vaccines and past illness stimulate the formation of not only antibodies, but also T cells, and this branch of immunity is more resistant to mutations.
Possibly less dangerous for the vaccinated
Huge statistics on the vaccinated show that even after the arrival of the “delta”, the protection against a severe course in the vaccinated remains at the level of 90%, although the protection against infection has dropped. Compared to ancestral strains, the spike protein sequences, which are recognized by T cells (they respond to small linear fragments), have changed in the alpha and delta strains. by about 10%… In the case of the omicron, possible changes are estimated within 20–30%… That is, it can be expected that T cells developed against the previous variants of SARS-CoV-2 will retain good activity against the omicron.
It is difficult to say unequivocally whether people who have T cells against other versions of the coronavirus actually retain protection against severe symptoms. In the early days, the number of hospitalizations in South Africa did not increase or increased very slowly, but now this figure has grown significantlyand the number of people requiring mechanical ventilation has also increased. The age composition is also gradually shifting: the number of elderly people in hospitals is increasing every day. This is an expected process if we assume that the pathogenesis of omicron is similar to that of delta: older people and those with chronic diseases are more likely to get seriously ill, including sometimes after vaccination. Their bodies are not able to properly fight the virus, and even two or three doses of the vaccine may not be enough help.
Another alarming factor is the high percentage of hospitalized young children. This African cohort is almost 100% unvaccinated, and the unusual representation of children among severely symptomatic patients may indicate that omicron alone without antibody and T cell insurance could be dangerous. However, for unambiguous conclusions, it is necessary to wait for better statistics, it cannot be ruled out that a large number of children are an artifact of the first weeks of the spread of a new strain and increased attention to any manifestations of the disease.
But something about the omicron can already be said unequivocally: according to the results of laboratory experiments, German virologists found that it became invisible to both monoclonal antibodies included in the Regeneron cocktail. Monoclonal antibodies are drugs that are given intravenously in the early stages of the disease. It is a series of ultra-high-performance antibodies against coronavirus artificially synthesized in a laboratory. Usually monoclonal antibodies are prescribed to patients from risk groups who, with a high probability, will not be able to fully develop their own immune response. They several times reduced the risk of bad outcomes, but against the omicron, a cocktail that worked against other strains is apparently useless. The good news is that two other early intervention drugs – Merck’s molnupiravir and Pfizer’s paxlovid – are likely to remain effective because their activity is not associated with spike protein.
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