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Omicron infection less likely than Delta to cause long COVID

Omicron infection is associated with a much lower odds of developing long COVID among those who have been vaccinated against the virus

The risk of developing long covid among those who have been fully vaccinated but who experience a breakthrough infection, is much less likely after infection with the Omicron than the Delta COVID-19 variant, according to the findings of an analysis of data in the COVID Symptom App study.

In November 2021, the World Health Organization designated the variant B.1.1.529, a variant of concern and named it Omicron. Fortunately, in an early assessment omicron infection cases, it appeared that there was a significantly reduced odds of hospitalisation compared to infection with the delta variant. However, the Omicron variant has been found to spread more easily than earlier variants of the virus. Consequently, though an omicron infection is likely to be milder, this could easily be offset by a higher level of infection and considerable disruption to society due to sickness, lost productivity and the exertion of additional pressure on health-care systems due to staff absences. Although an Omicron infection severe, what is less clear, is the extent to which the variant can induce long covid among those who experience a breakthrough infection. This is especially relevant given the recognition that long COVID can still arise in those with a mild infection.

Using data from the COVID Symptom App (which enables individuals to self-report COVID-19 symptoms, vaccination status and a host of other measures via a smartphone app), researchers compared the incidence of self-reported long covid among those who were vaccinated, during the Delta period (June 2021 to November 2021) and the Omicron period (December 2021 to March 2022). Individuals were included if they reported a positive PCR or lateral flow test after vaccination and at least one log per week on their smartphone app. Data were collected on age, gender, the index of multiple deprivation, co-morbidities, vaccination status and body mass index). The odds of developing long covid were calculated and determined with reference to the last reported vaccination as either 3 months, 3 – 6 months or > 6 months, with this latter category included to allow for possible waning immunity.

Omicron infection and long COVID

A total of 56,003 UK adults reported testing positive during the Omicron period and 41,361 individuals tested positive during the Delta period. Both groups had a high proportion of female participants (55% for Omicron and 59% for Delta) although the mean age was similar (53 years), as was the level of self-reported co-morbidities (approximately 19%).

Among those with an Omicron infection, 4.5% of participants developed long covid compared to 10.8% of those after infection with the Delta variant.

The odds of developing long covid after an Omicron infection was 0.26 (95% CI 0.20 – 0.32) if vaccinated > 6 months ago, 0.24 (95% CI 0.19 – 0.32) if vaccinated 3-6 months earlier and 0.50 (95% CI 0.43 – 0.59) if vaccinated < 3 months earlier. A similar reduction in risk was evident among those 18 to 59 years of age and for participants > 60 years of age.

The authors concluded that given there were over 350,000 COVID-19 infections reported on the app in March 2022, if only 4% develop long COVID, this still represents a sizeable number of long covid cases and which will inevitably rise, as case number increases.

Antonelle M et al. Risk of long COVID associated with delta versus omicron variants of SARS-CoV-2 Lancet 2022

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