Berlin After the reports from South Africa and Great Britain, it should no longer surprise anyone that the latest coronavirus variant, Omicron, is now also spreading rapidly in Germany. The reason for this is not only Omicron’s increased infectivity, about 2.5 to 3.5 times more contagious than the Delta variant, but also the pronounced ability to “immune escape”:
Doubly vaccinated, healthy middle-aged people also contract Covid-19. Those who have been vaccinated twice are only protected by around 25 percent from an infection, with a booster vaccination it is around 80 percent.
Pathogens, from the corona virus to the malaria parasite, have always found ways to “escape” the human immune system. Such “immune evasion” is found, for example, in the causative agent of sleeping sickness, a tropical disease that is fatal if left untreated.
The unicellular organisms, trypanosomes, can exchange the molecules on their cell surface at regular intervals and thus change their appearance. By the time the immune system has recognized the new pattern and formed suitable antibodies, the pathogen has already transformed again.
The omicron variant has at least two tricks up its sleeve to prevent antibodies formed by the immune system after an infection or vaccination. The spike protein, with which the viruses enter the cells, has 37 mutations at omicron compared to the original Sars-Cov-2 virus from Wuhan. 15 of them are found at the crucial point with which the spike protein docks onto the ACE-2 receptor of human cells.
molecular key
Of the 15 changes, nine are located in one subunit, the receptor-binding motif. In a way, it is the molecular key with which the virus manipulates the ACE-2 receptor in such a way that it can get inside the cell. The immune system’s antibodies, which can glue this receptor-binding motif together, prevent the key from entering the “ACE-2 lock”.
However, in the case of Omicron, the receptor-binding motif of the spike protein has changed significantly compared to the original spike molecule, which the body’s defenses knew from vaccination or illness with the virus type from Wuhan: the antibodies are no longer “precisely fitting”, the isolation of the spike -proteins from the receptor no longer function properly.
The research group led by molecular biologist Rommie E. Amaro from the University of California, San Diego, discovered another trick. The scientists have developed a computer model of the spike protein in which the three-dimensional structure is reproduced atom by atom. The atomic forces that hold the spike protein together in its three-dimensional form can be visualized in the model.
The scientists observed that the spike protein in omicron is more electrically positively charged than was the case in earlier variants. This in turn causes sticky sugar-protein molecules, called mucins, secreted by the mucous membrane in the nasopharynx to “cling” more tightly to the spike protein and thus protect the receptor-binding motif from attack by antibodies.
Shortly after the discovery of the omicron variant in South Africa, virologists checked in the laboratory whether protective antibodies produced by disease or vaccination were able to “neutralize” omicron, i.e. render them harmless.
It turned out that the antibodies produced by the immune system after an infection with the delta variant had already decreased so much after three months that they were no longer able to neutralize Omicron. This finding prompted the federal government to reduce the convalescent status – i.e. the period in which a convalescent is protected from infection by antibodies – to three months.
The best possible protection against severe Covid-19 disease or even death caused by it is still vaccination – even if even the triple vaccination cannot completely rule out an infection with Omikron.
(Photo: dpa)
A group led by the virologist Annika Rössler from the Medical University of Innsbruck has investigated how well blood serum from people who have been immunized with different vaccination schemes inactivates the alpha, beta, delta and omicron variants.
While there was virtually no difference between the older virus variants, the neutralizing effect of the blood sera on Omicron was seven to eight times less than that of the Delta variant. After a double vaccination with the Astra Zeneca vaccine, no neutralizing effect was detectable at all.
After a primary immunization with one of the two mRNA vaccines from Biontech/Pfizer or Moderna, a low neutralization capacity was retained. A booster with an mRNA vaccine increased the neutralizing property of the serum against omicron, but remained well below that against delta.
What the findings from the virological tests mean for reality, i.e. how well the vaccines still protect, can be derived from population-based studies from Denmark, Canada and above all Great Britain: A double vaccination with the Astra-Zeneca vaccine still protects against severe Covid 19 disease after omicron infection, but no longer before a mild course of the disease, scientists from the UK Health Security Agency showed in mid-December.
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After a double vaccination with the Biontech vaccine, the protective effect was still 88 percent on average in a period of two to nine weeks after the second dose, but dropped to 37 percent 15 weeks after the second vaccination. A booster with the Biontech vaccine increased the protective effect to 76 percent. For comparison: For Delta, the protective effect 15 weeks after the primary vaccination with the Biontech vaccine was 64 percent and 93 percent after the booster.
But which vaccination schedule now offers the best protection against omicron-related Covid-19 disease? To do this, researchers from the UK Health Security Agency evaluated data on a total of around 170,000 cases of Covid 19 diseases after delta infection and 204,000 cases after omicron infection. It was shown that the protection against a mild form of the disease after double or booster vaccination decreased almost twice as fast in an infection with omicron than in an infection with the delta variant.
People who received a primary series of the Biontech vaccine and then a booster with the Moderna vaccine were – at least over a two-month period – slightly better protected against Omicron than after another Biontech booster. The protective effect against a serious illness dropped to 52 percent when infected by Omicron six months after the primary immunization.
After a booster vaccination with an mRNA vaccine, the protective effect increased significantly to 88 percent, but did not reach 100 percent. This means that even after a booster vaccination, about every tenth adult can expect a severe course of the disease.
In Germany there is neither a vaccination register nor a database on emergency treatment in hospitals, which is why studies like those in Denmark and Great Britain cannot be carried out here. The government is therefore still dependent on data from other countries for the adjustment of anti-corona measures, for example for the readjustment of the vaccination schemes in view of Omikron.
For example, those who received the vaccine from Johnson & Johnson, which was originally intended to protect against Covid-19 with a single dose, now have to provide evidence of a second vaccination and a booster vaccination with an mRNA vaccine to protect against 2G and 2G+ respectively – rule to fulfill.
The cause of all this is a virus evolution that has produced a pathogen variant that is so infectious that extremely high 7-day incidences are measured everywhere in Europe, and that also manages this in countries with vaccination rates of over 90 percent – because Omikron has a has a previously unobserved ability to subvert the immune system.
This article first appeared in the Tagesspiegel.
More: “It’s not a banal cold”: What you need to know now to survive the omicron peak