It remains unclear whether the omicron coronavirus variant causes less severe disease, but even if this is true, hospitals could still be overwhelmed by the sheer number of cases
6 December 2021
There is growing evidence that the new omicron variant of the coronavirus is capable of spreading rapidly in populations with immunity against other coronavirus variants. It has already reached many countries and appears poised to cause a huge wave of infections around the world.
The big unknown is whether omicron is more or less likely to cause severe disease and deaths. Aris Katzourakis at the University of Oxford says he very much doubts the variant’s mutations will result in decreased severity, but that it is too early to tell.
“We are all worried,” says Katzourakis. “We are waiting with bated breath.”
In South Africa, where the variant was first detected, cases are rising even faster than during previous waves, with case numbers doubling every three to four days.
The rapid spread in South Africa doesn’t necessarily reflect what will happen elsewhere. The beta variant that was first spotted in South Africa and caused its second wave didn’t result in similar spikes in cases in other nations. However, there are signs that omicron is already taking off in different countries too.
For instance, the UK is seeing a rapid rise in so-called S-gene dropouts in PCR covid-19 tests, a phenomenon that happens when a variant has certain mutations in the gene for its spike protein. This is likely to be due to omicron. Denmark, which does a lot of sequencing, has already detected nearly 200 cases of covid-19 caused by this variant.
The main reason omicron is spreading so fast appears to be that it is excellent at evading prior immunity. Researchers in South Africa have found that the risk of reinfection is much higher with omicron. This suggests that the risk of vaccinated people getting infected is also much greater than it is with delta. Initial case reports back this up. For instance, of 11 omicron cases in Israel so far, six are in people who had had three doses of the Pfizer vaccine.
Besides potentially being able to evade immunity, omicron might also be inherently even more transmissible than delta. This remains uncertain, but there are already three reports of superspreading events where an extraordinarily high proportion of people were infected at parties in Norway, Denmark and the UK.
The good news is that the expectation is that people infected despite vaccination or prior infection will still be less likely to become severely ill than those with no prior immunity, as with delta. This is because while omicron may be able to evade antibodies, it is much harder for it to escape immune cells called T-cells that help clear viral infections. We also have much better treatments now, though they are mainly available in high-income countries.
Because of the lag between people getting infected, becoming seriously ill and recovering or dying, it could be many weeks still before it becomes clear just how well vaccination or prior infection will protect against severe disease, and how severe omicron will be in those with no prior immunity.
During a press conference on 3 December, Waasila Jassat at the National Institute for Communicable Diseases in South Africa said the country has already seen a sharp increase in hospitalisations in all age groups. Notably, children under 5 were the second biggest group after people aged over 60.
We will have to wait to see how those being hospitalised fare. One hospital in South Africa said that fewer covid-19 patients than normal were requiring oxygen as of 2 December, but cautioned that it is too early to draw conclusions.
Even if a smaller proportion of those infected with omicron become severely ill than was the case with previous variants, if it infects huge numbers of people, hospitals could still be overwhelmed.
“I’m hoping that prior immunity protects against severe outcomes, but I’m very concerned about the size of the epidemic wave in the US and across the world,” tweeted Trevor Bedford at the Fred Hutchinson Cancer Research Center in Seattle.
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