Delta Variant of Concern in COVID-19

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The Delta variant is the most recently designated variant of concern (VOC), as classified by the World Health Organization (WHO). This variant is now seen across the world, though it may have geographic origins in India. It is essentially the B.1.617.2 lineage and has likely contributed to the fast spreading and now the faster recovering Indian second wave. It seems to have high transmissibility but appears to be less virulent (lower case fatality, but there is a need for better documentation for a better evidence base). There was an explosion of cases due to its cluster spreading nature, which had overwhelmed the health care system. The symptoms may be more severe and include gastrointestinal issues such as nausea, diarrhea, abdominal pain and loss of appetite, as well as hearing loss, gangrene and blood clotting. A better natural history data is still awaited. The public health and the clinical approaches to the Delta variant cases appear to be similar to that of standard COVID-19 treatments.

The biggest concern with the Delta VOC is the immune escape it may have with the Oxford-AstraZeneca/Covishield and the Pfizer-BioNTech mRNA vaccines.

Aziz Sheikh et al, on behalf of Public Health Scotland and the EAVE II Collaborators, recently wrote in The Lancet about the impact of the Delta strain on the Scottish population. They wrote on May 19, 2021 that the Delta VOC has rapidly become the dominant strain of SARS-CoV-2 in Scotland replacing the Alpha VOC, which had earlier been the dominant strain.

EAVE II is a Scotland-wide COVID-19 surveillance platform that has been used to track and forecast the epidemiology of COVID-19, inform risk stratification and investigate vaccine effectiveness and safety. They used the EAVE II platform to undertake a cohort analysis to describe the demographic profile of COVID-19 patients, investigate the risk of hospital admission for COVID-19 and also estimate vaccine effectiveness in preventing COVID-19 hospital admissions in S gene-positive cases. Their analysis covered the period from April 1 to June 6, 2021, for the demographic distribution of cases.

By April 1, 2021, 44.7% of the population in Scotland had received one dose of the COVID-19 vaccine, and 7.6% had received two doses. Among people aged 65 years or older, the percentages were 91.2% and 15.9%, respectively. By the end of the study period (i.e., June 6, 2021), 59.4% had received one dose and 39.4% two doses; the corresponding proportions were 91.7% and 88.8%, respectively for those aged 65 years or older.

The researchers concluded that the Delta VOC in Scotland was found mainly in younger, more affluent groups. Compared to patients with Alpha VOC (B.1.1.7 lineage), the risk of hospital admission was approximately doubled in those with the Delta VOC; patients with five or more relevant comorbidities in particular were more likely to be hospitalised.

While both the Oxford-AstraZeneca and Pfizer-BioNTech COVID-19 vaccines were effective in reducing the risk of SARS-CoV-2 infection and COVID-19 hospitalization in people with the Delta VOC, these effects on infection appeared to be diminished when compared to those with the Alpha VOC. The numbers of hospital admissions to compare between vaccines in this respect were insufficient. The Oxford–AstraZeneca vaccine appeared less effective than the Pfizer–BioNTech vaccine in preventing SARS-CoV-2 infection in those with the Delta VOC. Since these are observational data, estimates of vaccine effectiveness need to be interpreted with caution.

Source: Sheikh A, et al on behalf of Public Health Scotland and the EAVE II Collaborators. SARS-CoV-2 Delta VOC in Scotland: demographics, risk of hospital admission, and vaccine effectiveness. The Lancet. Published June 14, 2021. DOI: