After analysing a symptom-tracking app, researchers found 4.5 per cent of users who were infected when the omicron variant was dominant had symptoms at least four weeks later, compared with 10.8 per cent of the users who probably caught delta
17 June 2022
People infected with the omicron coronavirus variant are less than half as likely to develop long covid, defined as symptoms lasting at least four weeks post-infection, as those infected with the delta variant, according to an analysis of a UK symptom-tracking app.
Nevertheless, the UK’s omicron wave is still likely to increase the total number of people with long-lasting health problems, given that the more transmissible variant has caused so many infections, says Claire Steves at King’s College London. “It’s important for people to know that it’s still possible to get long covid,” she says. “There are still a very large number of people being affected.”
Steves’s team used data from the long-running ZOE COVID app study, which asks people to enter information on their health and any positive covid-19 tests. The research group included about 56,000 people who were infected during the UK’s omicron wave, peaking in January this year, and about 41,000 people who tested positive last year when delta was the dominant variant.
To be included in the study, the participants had to be consistently reporting their health status on the app at least once a week and for a minimum of four weeks post-infection. All the participants had received at least one covid-19 vaccine.
Of those who were infected when omicron was dominant, about 4.5 per cent went on to have symptoms lasting more than four weeks, compared with 10.8 per cent of the participants who probably caught delta. The researchers didn’t assess any difference in long covid severity between the two groups.
According to Steves, the finding isn’t unexpected. Other research has shown that severe covid-19 is more likely to lead to long-lasting symptoms and the omicron variant has been causing milder illness than its predecessors. “Acute symptoms are strongly related to the risk of going on to get long covid,” she says. “But we also know that people not hospitalised can go on to have a very long and debilitating disease.”
The results contradict those from another UK study, however, run by the Office for National Statistics (ONS). In May, the ONS released data showing that in people who had received three covid-19 vaccines, about 8 per cent developed post-infection long covid – this time defined as symptoms lasting four to eight weeks – regardless of whether they caught delta or the BA.1 omicron subvariant specifically. The risk was slightly higher in people with the BA.2 subvariant, at about 9 per cent.
The ZOE study mainly included people who caught the BA.1 omicron subvariant, as it only analysed people who had been infected up to 10 February, before other omicron subvariants emerged.
Hannah Davis at the Patient-Led Research Collaborative, an international group of medical researchers who themselves have long covid, points out that the ZOE study and the ONS research defined long covid differently. The ZOE study’s four-week cut-off may miss some people who develop new symptoms after that time, she says.
Journal reference: The Lancet, DOI: https://doi.org/10.1016/S0140-6736(22)00941-2
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