Dec 31: What we know about the Omicron variant so far
Two studies, both released this week, confirmed the T Cell connection to the theory that Omicron is likely to lead to milder disease than Delta did.
New studies released this week now confirm what was thought to be the second reason why Omicron is likely to lead to milder disease than Delta did.
The adaptive component of the human body continues to recognise cells infected by the new variant of concern (VOC), eliminating them before they multiply to such a large extent that the disease becomes severe.
At play is what is known as the T Cell immunity, which has two sorts of cells – helper (CD4) and killer (CD8). These are different from antibodies, which are synthesised by B cells.
The Omicron variant has mutations that can cheat the antibody response but, as the new studies show, they are still susceptible to the killer cells. At least partly, this explains why the disease is halted before it gets more serious.
Studies published earlier this month showed the Omicron variant was significantly less capable in binding to lung cells and most of the people infected in hot spot regions of South Africa and UK were vaccinated or had a past infection -- two other factors attributed for the variant’s possibly decreased virulence.
The first new study on T cells was carried out by researchers in South Africa, who took samples from a group of 70 people that included people with prior Covid-19 and full vaccination with the Pfizer-BioNTech and J&J vaccines.
The researchers found that that “70-80% of the CD4 and CD8 T cell response to spike was maintained across study groups” and that the intensity with which the T cells reacted with the Omicron variant was similar to magnitude of when they reacted with Beta or Delta variants, “despite Omicron harbouring considerably more mutations”.
There was a fear that this would not happen – a virus that has changed drastically will be better able to fool the body’s defences. Omicron has 32-36 mutations in the spike protein (the protrusion that latches onto target cells) while Beta, the most resistant variant prior to Omicron, had only 11.
Thankfully, the T cell response recognises all of the spike.
The second study, by another group that was based at the La Jolla Institute in California but collaborated with the first group, had a more detailed quantification of the T cell response. They found that “84% and 85% of CD4 and CD8 T cell responses were preserved”.
How significant is this?
It reinforces the need for vaccination. All vaccines elicit a repertoire of immune response, including B cell and T cell responses. People who may be completely immune naïve will lack the T cell response that the researchers found in their studies.
The second is that the evolution of the S protein must be monitored to see the degree to which it changes. A spike that changes more of the “epitopes” – the locations that T cells recognise – would mean even this adaptive immune response would be lost.
“The resilience of the T cell response demonstrated here also bodes well in the event that more highly mutated variants emerge in the future. We still need to see how long T cell immunity lasts, but after Sars1 it was still detectable after 17yrs,” said Wendy Burgers, one of the South African researchers in a tweet.
The La Jolla team added in their report: “Nevertheless, the data also underline the need for continued surveillance and the potential danger posed by continued variant evolution that could result in further reduction of T cell responses.”