A health care worker in South Africa preparing vials of the Pfizer/BioNTech vaccine. Photo: Rodger Bosch/AFP (Getty Images)
The first glimmers of data on the Omicron variant of the coronavirus are starting to come in, and the verdict is decidedly mixed. Early experiments have found that antibodies from vaccinated people are clearly less able to neutralize Omicron in the lab, if not rendered completely useless. But antibodies generated through natural infection and vaccination combined, or with a booster shot, seem to be more robust. There remain many questions, including how these results will translate over to the real-world immunity created by the vaccines or past infection.
Omicron has unnerved pandemic experts due to its many mutations that threaten to make it better at evading the immune system of those protected via vaccines or past infections. It may also be better at transmitting between people, similar to other successful variants like Delta. Scientists worldwide have been working around the clock to learn more since the discovery of the Omicron variant around the Thanksgiving holiday. Yesterday, researchers from the Sigal Lab in South Africa were some of the first to release data from neutralization experiments involving the variant.
In response to infection or vaccination, the body’s immune system will create antibodies to that specific germ. Neutralizing antibodies are those that can stop these foreign invaders from infecting the body’s cells and replicating en masse—effectively cutting down the infection before it really begins. When it comes to covid-19, the immune system’s antibodies have learned to recognize the oldest version of the coronavirus that spread worldwide last year. Omicron may look or behave differently enough to evade some of the built-in defense provided by them.
In the lab, the researchers collected antibodies from people recently vaccinated with the Pfizer/BioNTech shots, as well as those who were previously infected and then vaccinated, and tested them against the classic coronavirus and Omicron. As many expected, levels of antibodies from the vaccinated that could neutralize Omicron declined substantially relative to the older strain. Overall, neutralization levels on average dropped 40-fold, to the point that these antibodies wouldn’t be expected to prevent infection most of the time.
At the same time, there was good news to be found, the researchers said. For one, the virus still relies on using ACE2 receptors to infect our cells, meaning it hasn’t radically changed its approach to infection. And while neutralization levels did decline for those with hybrid immunity from vaccination and past infection, these levels still remained above the threshold where you would expect strong protection from Omicron regardless. Even for people only vaccinated with two shots, the results don’t indicate that Omicron can completely evade their antibodies. The findings for those with hybrid immunity bode well for those who have gotten a booster shot, since it suggests extra exposure to the virus results in stronger immunity.
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“The fact that it still needs the ACE2 receptor and that escape is incomplete means it’s a tractable problem with the tools we got,” said Alex Sigal in explaining his team’s results on Twitter yesterday.
This morning, Pfizer announced its own early research results on Omicron, reporting that the original shots may not provide protection against infection from the variant. But it also found that, one month after a booster dose, people’s blood had levels of neutralizing antibodies against Omicron 25-fold higher than those vaccinated with two shots—enough to provide similar protection as the vaccines did against past strains, Pfizer concluded.
Neither the data from Pfizer nor from the Sigal Lab have been made available to other researchers yet, though a preprint is said to be forthcoming from the latter group very soon. And these results are based on a very small sample size, so they should be viewed with caution. Many other research groups will no doubt be releasing their own findings soon, which will give us a better idea of Omicron’s resilience against our immune systems.
Perhaps most importantly, we don’t have a firm grasp on what this will all mean in the real world. The original vaccines may still largely prevent the risk of severe illness and death from Omicron, particularly since we still have other aspects of coronavirus-specific immunity, like our T cells and memory cells. Or it’s possible that Omicron is inherently milder than past strains. So far, the case data from countries like South Africa, where many people have been previously infected and some vaccinated, isn’t clear one way or the other.
But given the benefits of boosting that were apparent even before the emergence of Omicron, it’s very likely that an extra shot will help there as well, along with continued public health measures like mask-wearing, ventilation, and testing.