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30 November 2021

Omicron variant: the case for cautious optimism

The government is right to act quickly, but vaccines may still be effective – and evolution itself might act in our favour.

By Michael Barrett

Late last week, the news broke that many had been dreading. A new coronavirus variant was found in South Africa. In this mutant, the S antigen – the spike protein that sits at the virus’s surface and docks on to our cells in order to invade them – has diverged considerably from the original variant detected in Wuhan late in 2019. It is on this latter variant’s S antigen that most of the Covid-19 vaccines depend.

Worse still, this new variant – quickly named after the Greek character omicron – appears to be even more transmissible than the Delta variant that emerged at the end of last year and rapidly became the predominant strain worldwide. Confronted with a highly transmissible virus – one that could have mutated enough to bypass the vaccine-induced immune responses trained on the original virus’s spike protein – it looked as if we might be back to square one. A terror virus, running through the population even more quickly that its progenitor forms, unchecked by the protective barriers the vaccines had induced in hundreds of millions of people.

More fool us, many might say. “None of us is safe until all of us are safe,” became a common refrain. As the Delta variant spread through the UK, Gordon Brown reminded us that by not vaccinating globally, we set ourselves at risk of just such an outcome. If left to foment in people, especially immunosuppressed individuals who are unable to kill the virus, evolution can select for increasingly effective mutations until, hey presto, a super virus is born. Governments sitting on their vaccine stockpiles would be proved foolish in their shortsighted nativism: those vaccines would have better-protected their own populations if they’d been given to people in faraway places.

The UK government has, for the first time since the pandemic began, acted at a speed that was woefully absent when previous variants arrived. The dilly-dallying when the virus first struck, followed by prevarication as the Alpha variant spread from Kent and procrastination when Delta hit, cost lives and billions of pounds. Stopping flights from afflicted countries, increasing testing and quarantine, re-mandating mask-wearing and implementing other social distancing measures makes sense while we assess what Omicron really does.

But will people who have been ignoring the rules for months now actually oblige? The Prime Minister, after all, never seems too bothered about the rules. And if the biggest danger of this new variant is its possible ability to beat the vaccines, why are people being told to get a vaccine or booster immediately?

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In fact, that isn’t so illogical. The S antigen has hundreds of possible sites along its length, called epitopes, to which antibodies can bind. Some are “preferred” – easier for the immune system to hit – and in most of us this is what happens. But additional doses of the vaccine can also bring new epitopes into view, making the virus more vulnerable to antibodies and also allowing T cells, which identify infected cells and kill them, to deprive the virus of its home.

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This means the old vaccine can indeed improve our responses even to the new virus, although amending the vaccine structure to the specifics of the new variant would be better still. To adapt, test and deliver modified vaccines would take several months, but vaccination is a long road – less than half the world’s population has had even a second jab.

There is another possible outcome. Early evidence indicated that, although Omicron appears more transmissible, it might be less virulent than its predecessors. This is far from unheard of in evolution. A virus that transmits readily, and is less dangerous to those who catch it, is the natural trajectory of an infectious agent. Pathogens need hosts in which to survive and reproduce, so killing those hosts has a long-term evolutionary cost. It’s been proposed that some of the other coronaviruses that cause common colds today evolved in just this way.

The first wave of Omicron cases in South Africa appeared to be largely mild, although the majority were found only in younger, fitter people, in whom cases of Covid-19 are generally mild. It is too early to know what might happen to more vulnerable members of the population. The number of people hospitalised in South Africa is now going up, as older and less fit people are infected.

The best-case scenario is that Omicron is much less virulent, but super transmissible. Such a variant could sweep around the world, infecting hundreds of millions of people without provoking the serious manifestations of its previous incarnations. People would develop immunity of a more profound and lasting kind than that conferred by vaccination.  

Even this would still be dangerous for many, however. The rapid spread would increase infection rates dramatically, and a lower-virulence virus that infects huge numbers of people quickly would still risk bringing the kinds of pressures on health services that have triggered lockdowns. The next few weeks, when scientists will assess the actual virulence, transmissibility and vulnerability of Omicron to vaccines, will be critical. Until then, implementing the government’s plan B is a sensible place to sit if we wish to avoid another national lockdown this Christmas.

Michael Barrett is professor of biochemical parasitology at the University of Glasgow.

[See also: Travel bans won’t defeat Omicron]

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