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Why COVID vaccines are partially effective against omicron

December 13, 2021

It's unclear whether omicron causes milder symptoms than other coronavirus variants — though experts still urge the public to get vaccinated. In the UK, at least one death due to the omicron variant has been confirmed.

In this photo illustration, a medical syringe and a vial are seen in front of the word omicron
Omicron is more infectious than delta, but it remains unclear whether it is also more dangerous Image: Pavlo Gonchar/Zumapress/picture alliance

The new coronavirus omicron variant has spread rapidly around the world.  It has already been detected in at least 57 countries on six continents.

Christian Drosten, the chief virologist at the Charite hospital in Berlin, is particularly concerned about the speed at which omicron is spreading. In South Africa and the United Kingdom, the number of cases is doubling every three to four days. 

Infografik Karte Omikron Verbreitung EN

Another cause for concern is that omicron can partially elude the protective effects of existing vaccines. This means that even those who are vaccinated, including those who have received a booster shot, can become infected with the variant.

Recent studies all show a strong, approximately 40-fold reduction in the neutralizing effect of antibodies in a number of combinations of vaccination and natural infection. This means that neither naturally nor vaccine-induced antibodies can bind the virus well and thus prevent it from entering the human cell. In other words, omicron has the potential to evade the body's immune response in some cases.

But the cellular components of the immune system still offer protection. Our T-Cells seem to be good at recognizing omicron — and T-Cells are an important part of our defense against infection. Vaccines should then maintain their efficacy and protect against severe infections, especially if the immune system is further stimulated through a booster jab.

Decreased effectiveness

According to Axel Sigal, a professor at the Africa Health Research Institute in South Africa, neutralization of the new coronavirus variant by BioNTech-Pfizer's active ingredient, for example, is much lower than with an earlier strain of the coronavirus. The vaccine thus offers only partial protection against omicron, he said.

The head of the US vaccine manufacturer Moderna, Stephane Bancel, also believes there is a significant decrease in the protective effect. That is because 32 of the 50 mutations in omicron affect the spike protein, which the coronavirus uses to enter cells. 

Most first-generation COVID-19 vaccines target the spike protein, and because of these mutations, the neutralizing antibodies induced by COVID-19 vaccines are less able to bind to it.

This probably affects all existing vaccines. That has also been confirmed by Frankfurt-based virologist Sandra Ciesek on Twitter. Ciesek, who is is director of the Institute of Medical Virology at the University Hospital Frankfurt am Main, stresses that the development of a vaccine adapted to omicron makes sense based on the data available so far.  

Why is omicron more contagious?

Researchers are currently analyzing the new virus variant under high pressure. Investigations by the US company Nference have discovered a gene sequence in omicron that may make the mutated virus more contagious. That is because this unusual gene material is also found in viruses that trigger conventional colds.

Until now, the sequence has been known mainly from the human coronavirus HCoV 229E, which can infect humans and bats. The omicron variant has thus been able to adapt better to the human host, believes Venky Soundararajan, bioengineer and co-author of the study.

The mixing of genetic material from the two virus strains could have happened within a human organism, according to the study. Cells in human lungs could have been infected by both viruses so they could combine there.

Is omicron less dangerous?

Renowned health experts such as Dr. Anthony Fauci, the coronavirus adviser to US President Joe Biden, cautiously described the findings to date on omicron as somewhat encouraging in terms of the expected severity of the disease.

He posited that while the virus may be more contagious, the cases of the disease it causes may be milder.

But at the same time, Fauci also made it clear that this is not certain and cautioned about making judgments on whether omicron is less dangerous or really causes less severe disease than delta.

On Monday, December 13, 2021, the UK recorded that at least one person had died with the omicron variant of the coronavirus.

Initial reports from doctors in South Africa had indicated that omicron could lead to milder forms of the disease. 

But there are no really reliable statements about the severity of COVID-19 disease after infection with the omicron variant. In South Africa, for example, only 42 cases have been studied in detail. The significance of the study is therefore very limited. According to the paper, the age of those infected has fallen in comparison to other variants: More than 80% of those infected with the omicron variant are under 50 years old.

Infografik Corona-Fälle in Südafrika EN

In addition, those affected spend less time in hospital: While hospital stays lasted 8.5 days on average before omicron, they are only about 2.8 days with omicron, according to a statement by the virologist Fareed Abdullah of the South African Medical Research Council. But further studies are urgently needed, Dr. Abdullah stresses.

All this says little about whether omicron also tends to cause milder forms of the disease in older infected persons. According to virologist Drosten, it could well be that the severity of the disease actually increases. Not only does the virus multiply more, but the omicron variant also has the "stupidest combination" of properties, he argues: immune escape and fitness gain.

"A lot of virus, a lot of disease," Drosten said in his regular podcast with the German public broadcaster NDR.

Is it good if omicron displaces the delta variant?

The rapid spread of omicron could mean that it is displacing the delta variant, which has been dominant until now, meaning that a very contagious but probably more harmless variant may be displacing a variant that is demonstrably very contagious and very dangerous. This sounds promising at first, but no one can yet reliably assess whether this will actually mitigate the pandemic.

Johannesburg struggles under omicron surge

A new mutation does not necessarily have to be more dangerous. Experts already emphasized this when the first variants became known. Often, viruses also lose their potency through numerous mutations, or they produce so many copying errors during the reproduction process that the viruses become ineffective, as was recently observed with the delta variant in Japan.

All the same, the omicron variant will keep us in the grip of the pandemic for months to come, warned Charite virologist Drosten: "The delta virus is our problem until January; the omicron virus is our problem until summer."

Do vaccinations and boosters still make sense despite the omicron variant?

Definitely yes! It is true that the existing vaccines are expected to further lose effectiveness due to the omicron variant. But this does not mean that they have no effect at all, experts emphasize. BioNTech argues that the third booster shot will reduce the danger of hospitalizations even with omicron.

Vaccinations and boosters with the existing vaccines also protect against severe disease progression and deaths, experts agree. And that is precisely why it is so important that those who have yet to be vaccinated are protected and that the booster vaccination campaigns are accelerated. 

This article was originally written in German. Edited by: Timothy Jones. It was last updated on December 13, 2021, adding new insights on the ability of T-Cells to recognize omicron. The update was edited by Fabian Schmidt.