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Making Sense of the Omicron Variant’s Competitive Edge

Making Sense of the Omicron Variant’s Competitive Edge

A 3D print of a spike protein of SARS-CoV-2 in front of a 3D print of a SARS-CoV-2 virus particle. Photo: NIH/Flickr, public domain

  • A new study has found that if you recover from an infection of the omicron variant, you may also be able to fend off an infection by the delta variant.
  • The study was conducted with a small number of people in South Africa, and its results are as such preliminary.
  • But if its findings are replicated in more studies and if we minimise the emergence of newer variants, the rise of omicron may be the beginning of the end of the pandemic.

There is already empirical data that the omicron variant is rapidly displacing the delta variant as the dominant strain wherever it is spreading. New results reported from South Africa have also found now that if you recover from an infection of the omicron variant, you may also be able to fend off an infection by the delta variant.

For their study, Alex Sigal and his team at the Africa Health Research Institute, Durban, conducted a simple test. They enrolled a small group of patients who had recently had an infection of the omicron variant, and identified seven who had been vaccinated and six who hadn’t. Then, they asked: Would these people be able to fight off the delta variant?

According to their study’s preprint paper, the researchers collected blood samples from the 13 volunteers twice – once when they enrolled and again two weeks later. They assessed the capacity of antibodies in all these samples to neutralise the delta and the omicron variants. Finally, they determined the neutralising antibody titres in all samples at the two time points.

At the start of the study, the blood samples had a low capacity to neutralise the  omicron variant. The mean omicron-neutralising antibody titre was 20 – a low value that was expected as the people had just contracted the omicron variant infection and wouldn’t have had enough time to develop significant levels of anti-omicron antibodies. The same samples displayed a mean delta-neutralising antibody titre of 80 – a number that presumably reflects the outcome of past natural infection and/or vaccination.

But two weeks later, the mean omicron neutralising antibody titre rose to 285, greater than 14x. And the mean delta-neutralising antibody titre rose to 354, a four-fold increase.

It is evident from these numbers findings that, two weeks after an omicron variant infection, the capacity to neutralise the delta variant increases noticeably. The increase was also higher in the group of vaccinated individuals.

Omicron-induced antibodies don’t only neutralise omicron, as expected, but also neutralise the delta variant quite efficiently two weeks after an omicron-variant infection. The researchers interpreted this to mean that an omicron-variant infection could confer protection against a subsequent delta-variant infection. They also cited the results of an Austrian study: that antibodies in the blood of individuals infected by the delta variant neutralise the omicron variant poorly. This was also based on data from a virus neutralisation assay.

So it appears that while omicron-induced antibodies can neutralise the delta variant efficiently, the reverse is not true. This conclusion helps explain the competitive edge the omicron variant seems to enjoy and is consistent with its rapid displacement of the delta variant in countries around the world. This may perhaps be good if illness due to the omicron variant is truly mild; we don’t yet have conclusive information on this count.

Second, the finding that antibodies against the omicron variant neutralise the delta variant is surprising, because antibodies prompted by the delta variant don’t neutralise the omicron variant well. One reason could be the omicron variant’s heightened ability to evade antibodies. But even so, we don’t know the underlying reason for omicron-elicited antibodies to be able to neutralise the delta variant.

Is it because these antibodies are cross-reactive towards the delta variant? Is it because omicron-elicited antibodies are broadly neutralising and perhaps encompass other variants as well? Or is it because an omicron-variant infection ends up activating immune memory from prior infections and or vaccinations? Hopefully more studies will tell.

It is also important to remember that the Sigal et al. study is effectively preliminary, considering it involved a very small number of people.

In slightly more than a month, the omicron variant has taken the world by storm. Not only does it have a growth advantage over the delta variant, it is also more capable of overcoming immunity, both naturally and vaccine-induced. But on the plus side, we continue to find that it seems to cause mild illness.

If the current findings of the South African scientists do turn out to be true in further experiments, and if we scrupulously follow COVID-appropriate behaviour to minimise the emergence of new variants, we may have reason to hope that the rise of omicron may be the beginning of the end of the pandemic.

S. Swaminathan is a retired scientist based in Hyderabad. The views expressed here are the author’s own.

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