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Omicron: Partial immune evasion after vaccination

The Omicron variant of the coronavirus was first identified in South Africa on November 26, 2021. It has already spread to 62 countries all over the world, and may become the dominant variant in some European countries by as early as next week. 

Omicron does not seem to cause more severe illness. In fact, its symptoms appear to be milder than those of previous variants. However, its high transmissibility makes experts claim that Omicron will soon become dominant globally, giving rise to enormous waves of infections in most of the world’s countries.

In one of the first peer-reviewed studies about this variant (published in the journal Emerging Microbes & Infection), a research team led by China’s National Institutes for Food and Drug Control (NIFDC) has tested 28 serum samples from COVID-19 convalescent patients infected with the original strain of the coronavirus that emerged from Wuhan against in vitro Omicron samples (as well as other variants of concern and interest). 

The experts discovered that the neutralization potential of these sera against Omicron decreased 8.4 fold. This reinforces previous findings that argued that Omicron is capable of dodging immunity gained from previous infections.

“We found the large number of mutations of the Omicron variant did cause significant changes of neutralization sensitivity against people who had already had COVID,” said study senior author Youchun Wang, a researcher at NIFDC. “However, the average ED50 (protection level) against Omicron is still higher than the baseline, which indicated there is still some protection effect that can be observed.”

Wang and his colleagues predict that Omicron may be able to evade to a certain degree also vaccine-induced immunity, particularly since real-world data has already shown that the protection from vaccines diminishes significantly four to six months after the second dose. 

Pfizer and BioNTech have also reported earlier this week that sera from individuals who received two doses of their vaccine exhibit more than a 25-fold reduction in neutralization titers against the Omicron variant compared to the wild-type virus, and strongly suggested people to get a booster shot.

“Although two doses of the vaccine may still offer protection against severe disease caused by the Omicron strain, it’s clear from these preliminary data that protection is improved with a third dose of our vaccine,” said Albert Bourla, Pfizer’s Chairman and Chief Executive Officer. “Ensuring as many people as possible are fully vaccinated with the first two dose series and a booster remains the best course of action to prevent the spread of COVID-19.”

However, future real-world studies are essential for clarifying Omicron’s ability to evade previously acquired immunity and thus establish the potential global impact of this new variant. 

By Andrei Ionescu, Staff Writer

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