Ómicron causes fewer severe cases, but why? Scientists don’t know yet

The idea of omicron is less serious It has been present since minute zero, when, after characterizing the new variant, South African doctors began to see that almost all cases were mild despite the spectacular increase in infections. As of today, this question remains to be clarified, although little by little we are having more data. The latest is that several studies indicate that the percentage of hospitalizations it causes is significantly lower. However, it is not clear whether it is due to the characteristics of the virus itself or to the action of vaccines, because these do not behave the same in front of omicron as in front of delta.

One preliminary study published this week by the National Institute of Communicable Diseases of South Africa states that the risk of hospitalization was approximately 70% lower among people infected with omicron recently compared to those that had been infected by delta between April and November. However, once a patient is admitted, the risk of developing serious illness is the same. As they are different stages, the analysis leaves some doubts. In addition, experts consider that it is difficult to equate the South African and European data, due to the differences in the average age of the population (younger there), the percentage of vaccinated (lower) and of people who have already had the disease. (Supposed to be very high, although there is no precise data either).

For this reason, the first data from the United Kingdom was awaited with expectation, a country that has been badly hit by omicron and which has generated a lot of data early. The University of Edinburgh has just post a job in which he analyzes omicron and delta patients from November and December and concludes that becoming infected with the new variant reduces the risk of ending up in hospital by two thirds. Specifically, the researchers identified 15 admissions per omicron and calculated that with the delta statistics they would have been slightly more than triple. Around the same time, Imperial College London has offered data somewhat less optimistic. According to his calculations, with the new variant the need to be hospitalized for more than a day is reduced between 40% and 45%, although he adds that the risk of visiting the emergency room also falls between 20% and 25%.

In the absence of published studies, in Spain the Deputy Minister of Health Assistance and Public Health of the Community of Madrid, Antonio Zapatero, has announced the first data through your Twitter account, according to which the risk of suffering from pneumonia would be 73.5% lower with omicron than with the previous variants and the possibility of being hospitalized falls even more: 83.5%. These figures would be in line with other countries and would be even better.

A still questionable idea

This is certainly good news, although it may be too early to understand exactly what they are telling us. Experts remain skeptical that the new variant is actually milder on its own, because it is impossible to distinguish if the data have to do with a lower aggressiveness of the virus or they can be explained by the action of vaccines. To know for sure, you would have to measure something that has not yet been done by any study, at least with sufficient statistical relevance: compare unvaccinated people infected with omicron and unvaccinated people infected with other variants.

“It seems that the disease is milder because there are fewer hospitalizations, but they are occurring in a context with many vaccinated people or with many people who have passed the infection, as is the case in South Africa”, Warns in statements to Teknautas Sonia Zúñiga, virologist and researcher at the National Center for Biotechnology (CNB-CSIC). Even when comparing cases of delta and omicron in the same time space, as is the case of the United Kingdom, vaccination may be affecting the analysis because it does not have the same effect in the two variants. Being more effective to avoid contagion with delta, could be causing a statistical effect that distorts our perception of severity, since in the end there are many more cases of omicron, but since the vaccine is still effective against severe disease, a very small percentage of them end up in the hospital.

Other factors make it difficult to analyze the situation. For example, the lack of coupling between data on infections and those on ICU hospitalizations and admissions, an impact that is noticed weeks later and that can lead to a premature reading of the figures. The fact that a large part of the population has had the third dose very recently, in particular, the elderly who are the ones who enter the most, can also distort the data. Recent vaccination causes the level of antibodies to be very high and this, in turn, prevents many infections (possibly also with omicron, although it has a better ability to avoid them). Yes relatively young people are becoming infected to a much greater extent who received their second dose months ago, but are less likely to become seriously ill, we would be facing another distortion of the figures that prevents us from guessing if omicron is really milder.

What do Spanish doctors observe?

“In my office I’m not seeing older patients with third doses”Says Vicente Baos, doctor of Primary care. “The vast majority of those who arrive with symptoms are young people who have two doses and very mild pictures,” he says, although with the nuance that it is a subjective impression in the absence of studies that collect all the data. What is expected among those vaccinated is precisely that complications do not occur. “This lightness is induced by vaccination, apart from the fact that age and risk factors also influence”, remember.

The most important change that he has observed as omicron has been clearly imposed is in the duration of the symptoms: “The average is three days with mild symptoms and a very fast recovery, whereas before it lasted from five to seven days and the improvement was slow ”. These symptoms are usually low-grade fever, sore throat, headache, and dry cough; while other common characteristics of covid have disappeared, such as loss of smell and taste.

In any case, Baos considers that it is impossible to reach serious conclusions about the virulence of omicron. if we do not clearly distinguish between vaccinated and unvaccinated patients. “In a person who has not been vaccinated, we would have the expression of pure omicron, while among those vaccinated, the logical thing is that it is less serious. Mixing everything is not convenient. Over time, it will be seen what the percentage of unvaccinated that is complicated and that is admitted to the ICU ”, he points out.

Aside from population data, there is other research that seems to explain why omicron would be less aggressive. Preliminary investigations of the University of Cambridge and of the Hong Kong University indicate that the new version of the virus infects the upper respiratory tract very well but has more difficulty attaching to lung cells. However, virologists miss precisely having all the data from a regular, peer-reviewed scientific publication to be able to assess these findings. “If they have not used the natural virus, but a pseudovirus to which they have added the S protein, they may have studied very well how it enters cells, but we miss the effect of mutations in other virus proteins”, warns Zúñiga, ” so it is possible that it enters badly but it multiplies quickly ”.

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The real good news

So actually, the best news from all these studies is that they confirm that vaccines protect against serious disease, even omicron. Although it succeeds, thanks to its mutations, it manages to avoid antibodies and, therefore, infect human cells, “it has already been seen that the cellular response protects us and that, therefore, vaccines continue to be effective,” says the virologist of the CSIC. T-cell response remains at very high levels, according to the first analyzes, for example, University of Cape Town experiments and the data on hospitalizations caused by omicron seem to corroborate this.

“Nobody knows if the virus is more or less aggressive, but the most important thing is that vaccinated people, even if they are getting massively infected, has the protection of T cells”Confirms Marcos López Hoyos, president of the Spanish Society of Immunology (SEI). In theory, it is possible that this good response is influencing the symptoms to disappear sooner, but “we have no evidence if the contagion period is maintained”, so the recommendation to remain isolated for 10 days should be maintained.

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