Long-COVID risk reduced with Omicron versus Delta

In a recent study published in the lancetresearchers from King’s College London and ZOE Limited assessed the risk of long-term coronavirus disease (COVID) associated with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Delta and Omicron variants in the United Kingdom (UK).

Studies have reported that Omicron causes acute SARS-CoV-2 infections that are less severe than those of previously circulating variants, especially among vaccinated individuals; however, a large population can develop long-lasting COVID symptoms. Data on the relative likelihood of long-term COVID among those infected with relatively recent variants such as Delta and Omicron could inform health authorities and policymakers about a more appropriate allocation of health resources.

Correspondence: Long-term COVID risk associated with delta versus ommicron variants of SARS-CoV-2.  Image Credit: Donkeyworx/ShutterstockCorrespondence: Long-term COVID risk associated with delta versus ommicron variants of SARS-CoV-2. Image Credit: Donkeyworx/Shutterstock

About the study

In the current case-control study, researchers evaluated the risks of prolonged COVID during the periods of Delta domination and Omicron domination among UK citizens.

The ZOE application for COVID symptoms study was used to obtain data reported by subjects with real-time polymerase chain reaction (PCR) confirmed or lateral flow antigen test confirmed COVID 2019 (COVID-19) diagnosis after vaccination. The study participants had no pre-vaccination history of COVID-19 and had ≥1 log of reported symptoms in the ZOE application weekly for ≥28 days.

For individuals who tested positive during Omicron domination, only those who tested SARS-CoV-2 positive before February 10, 2022 were included. For both groups of individuals, the index of multiple deprivations (IMD) for local areas was calculated to estimate relative local deprivation. For the index, a score of 1 represented the most deprived and a score of 10 the least deprived.

The study exposure was the period of infection and the study result was the development of long-term COVID. To determine the association between outcome and exposure, logistic regression modeling was used with data adjustments for long COVID risk factors such as IMD, gender, age, co-morbidities, body mass index (BMI), and vaccination status (single, double, or triple vaccine doses). receive). The period between the most recent vaccination and the development of SARS-CoV-2 infection was stratified into three groups, namely: three months, three to six months and >6 months.


A total of 56,003 Omicron cases (adults who initially tested SARS-CoV-2 positive between December 20, 2021 and March 9, 2022) and 41,361 Delta cases (adults who initially tested SARS-CoV between June 1, 2021 and November 27, -2 tested positive) 2021) were identified. The proportion of women with Delta (59%) and Omicron (55%) infections was significantly greater than in men.

However, both groups had participants of the same age (mean age was 53 years) with a similar presence of comorbid conditions (19%). IMD indices showed that cases of Omicron variants are common in regions with slightly less deprivation compared to cases of Delta variants (17% vs 17.5% with IMD scores of 1 to 3).

Among Delta and Omicron cases, 2501 individuals (4.5%) and 4469 individuals (10.8%) developed long-term COVID symptoms. The relative probability of long-term COVID was lower in Omicron infections compared to Delta infections for all vaccination times (odds ratio range between 0.2 and 0.5). Similar results were obtained by performing an age-stratified analysis.


Overall, the study results showed that long-term COVID risk was lower for individuals with Omicron infections compared to those with Delta infections; however, the absolute number of long-term COVID cases over a period of time depends on the amplitude and shape of the curve depicting the pandemic. Given the peak Omicron cases of >350,000 new and symptomatic COVID-19 cases estimated to have occurred daily on March 26, 2022, of which only 4.5 percent are long-term COVID cases as estimated by the ZOE app, The case numbers for long-term COVID-19 cases would only increase in the future.

The authors believe the current study is the first of its kind peer-reviewed to assess the risk of long-term COVID among Omicron cases. The findings highlight the use of smartphone applications in COVID-19 surveillance. However, further studies need to be conducted to determine whether unvaccinated children and adults are at greater risk for long-term COVID.

Study restrictions

The study limitations include the use of data reported by the SARS-CoV-2 positive individuals themselves without any direct SARS-CoV-2 test for variant identification and the absence of objective outcome measures for the duration of COVID-19. In addition, the review period for Omicron cases was shorter (though marginal) compared to Delta cases. In addition, individuals could not be assessed for long-term COVID risks for extended periods, for example, over 12 weeks.

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