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Omicron infection less likely to trigger long Covid than Delta, finds large study

Omicron infection less likely to trigger long Covid than Delta, finds large study

Patients are less likely to develop long Covid with Omicron, which is currently the dominant strain of the virus, a large study has found.

Analysing data from the ZOE symptoms study app, researchers concluded that 10.8% of patients who tested positive for Covid while Delta was the dominant strain reported long Covid symptoms.

However, since the Omicron strain took over as the most prevalent in the UK, just 4.5% of Covid-positive study participants developed long Covid.

The paper, published in the Lancet, said: ‘Overall, we found a reduction in odds of long Covid with the omicron variant versus the delta variant of 0.24-0.50 depending on age and time since vaccination.’

However, despite the decreasing risk, researchers predicted that more people are going to come forward with long Covid.

The paper said: ‘Considering the UK omicron peak of more than 350 000 new symptomatic Covid-19 cases per day estimated on March 26, 2022, by the ZOE app model and 4% of cases being long Covid, future numbers with long Covid will inevitably rise.’

Dr David Strain, clinical senior lecturer and honorary consultant at the University of Exeter Medical School, welcomed the study but said it was ‘important to say however that these data come from the omicron BA.1 period’.

He continued: ‘The Office for National Statistics suggested that the BA.2 variant that has caused much of the recent wave, did cause long Covid in triple-vaccinated people at approximately the same rate as the Delta.

‘Obviously, it is impossible to comment on the longer term impact of these variants as we are still in the early days. If the resolution rate for these people with omicron BA.1 remains at 50% between week 4 and week 12, and a further 12.5% for those who still have symptoms at 12 weeks, this will be very good news for all the healthcare services that are concerned about the potential number of long Covid patients over the next 2-3 years.

‘It is feasible, however, that those who got long Covid despite triple vaccination and the more mild BA.1 omicron variant are in some way more susceptible and may not follow the same course.’

And he said that ‘even 4.4% of the very large number who experienced Covid as protections were eased, creates a significant public health burden of this disease with no known treatment, or even reliable diagnostic test’.

This comes after RCN members last week voted for the organisation to campaign to tackle the ‘unfair’ and ‘immoral’ treatment of some nursing staff with long Covid who are facing a ‘postcode lottery’ of conditions.

In February, research found that people fully vaccinated against Covid-19 are around half as likely to develop long Covid symptoms as unvaccinated people or those who had only received one vaccine dose.

A version of this article was originally published on our sister publication Pulse. 

Methodology and results

Research cohort:

Omicron group: 56,003 UK adults first testing positive between Dec 20, 2021, and March 9, 2022, when more than 70% of UK cases were estimated to be attributable to the omicron variant.

Delta group: 41 361 UK adult cases first testing positive between June 1, 2021, and Nov 27, 2021, when more than 70% of cases were attributable to the delta variant.

Both symptomatic and asymptomatic infections were considered.

Results:

Among omicron cases, 2,501 (4.5%) experienced long Covid and, among delta cases, 4,469 (10.8%) experienced long Covid.

Omicron cases were less likely to experience long Covid for all vaccine timings, with an odds ratio ranging from 0.24 (0.20-0.32) to 0.50 (0.43-0.59). These results were also confirmed when the analysis was stratified by age group.

Source: Risk of long COVID associated with delta versus omicron variants of SARS-CoV-2, published in the Lancet

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