Should you go to that festive party this year if you want to avoid being infected by the coronavirus? Probably not. In addition to the risk posed by the high levels of the delta variant in many countries, the omicron variant is now spreading too – and it appears capable of infecting an astonishingly high proportion of people at social events.
There are already at least four reports of superspreader events at parties across Europe where a third or more of the people attending have been infected. Omicron hasn’t yet been confirmed in all cases but is likely to blame.
“The very high proportion of people infected at these events, taken together with the very rapid increase in cases in South Africa, point to a variant with possibly considerably stronger abilities to infect,” says epidemiologist Gunhild Alvik Nyborg of the Covid Action Group, an international thinktank on eliminating covid.
One of the events was a party at a restaurant in Oslo, Norway. Around 70 of the 120 people who attended the party were infected, as were another 50 people at the restaurant. Omicron has been confirmed by sequencing in 13 cases so far.
In Denmark, 53 of 150 people who went to a Christmas lunch in Viborg have been confirmed to be infected with omicron.
In Spain, 68 medics at the University Regional Hospital in Malaga have tested positive after going to a Christmas party at which 173 people were present altogether. It isn’t yet clear if any of the 68 have omicron.
In the UK, Tim Spector at King’s College London says he has been told of a 60th birthday party at which 14 of 18 people were infected with omicron according to PCR tests. All the guests were vaccinated and are said to have tested negative on lateral flow tests in the 24 hours beforehand.
“It definitely demonstrates a very high secondary attack rate,” says Tom Wenseleers at the Catholic University of Leuven (KUL) in Belgium.
Delta is more infectious than the original virus identified in Wuhan, but its spread is limited by the fact that most people now have immunity to it either from prior infection or vaccination. Omicron appears to be both more infectious than delta and much better at evading prior immunity, says Wenseleers.
We have seen superspreader events with other variants. In May 2020, for instance, at least half of the 61 people who attended a choir practice in Skagit County, Washington, became infected.
But to have so many events of this kind so soon after omicron reached Europe suggests the risk is higher. “This looks like it is in a different league,” says Nyborg.
She speculates that people can be infected by a smaller dose of omicron, increasing the likelihood of airborne spread. “Only a few viral particles lingering in the air likely now poses a larger threat than for earlier variants,” says Nyborg.
People should be avoiding these kinds of events as omicron spreads, says Spector. However, the risk of being infected by omicron also depends on the odds of someone with omicron being at a party, and that is low in most countries, for now.
“Hopefully this week the risks are still low,” says Spector. The risk might also be lower in theatres or concerts if people wear masks and there is good ventilation, says Nyborg.
Fear of oxygen shortages
However, delta variant infections are currently at high levels in many countries, including the UK, where 469 people in every 100,000 have had a positive PCR test in the past seven days.
The big unknown remains whether omicron is more or less likely than delta to cause severe disease. So far, all those infected at the parties are said to have mild cases, but it is too soon to be sure this will remain true.
People who become severely ill with covid-19 generally do so only around a week after symptoms first develop. In addition, most of those infected were young and therefore at lower risk.
However, attending parties isn’t just about the risk to you as an individual. If you become infected and infect others, you could contribute to a massive surge in cases that could overwhelm hospitals even if omicron is less severe than delta.
“We risk seeing a very large proportion of the world’s population infected at the same time, leading to shortages of oxygen,” says Nyborg.
“I want such events to be allowed as much as anyone else,” she says. “But from a scientific point of view, this is really high risk.”
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