SARS-CoV-2 Delta variant, also known as lineage B.1.617.2, is a variant of lineage B.1.617 of SARS-CoV-2, the virus that causes COVID-19. It was first detected in India in late 2020. The World Health Organization (WHO) named it the Delta variant on 31 May 2021.
It has mutations in the gene encoding the SARS-CoV-2 spike protein causing… substitutions… which are known to affect transmissibility of the virus as well as whether it can be neutralised by antibodies for previously circulating variants of the COVID-19 virus. Public Health England (PHE) in May 2021 observed secondary attack rates to be 51–67% higher than the alpha variant.
COVID-19 vaccines are effective in preventing severe disease or hospitalization from infection with the variant, although some evidence suggests vaccinated people are more likely to develop symptoms from Delta than other variants of SARS-CoV-2.
Variant of Concern
On 7 May 2021, PHE changed their classification of lineage B.1.617.2 from a variant under investigation (VUI) to a variant of concern (VOC) based on an assessment of transmissibility being at least equivalent to the Alpha variant; the UK’s SAGE (Scientific Advisory Group for Emergencies) subsequently estimated a “realistic” possibility of being 50% more transmissible. On 11 May 2021, the WHO also classified this lineage VOC, and said that it showed evidence of higher transmissibility and reduced neutralisation. On 15 June 2021, the Centers for Disease Control and Prevention (CDC) declared Delta a variant of concern.
The variant is thought to be partly responsible for India’s second wave of the pandemic beginning in February 2021. It later contributed to a third wave in Fiji, the United Kingdom and South Africa, and the WHO warned in July 2021 it could have a similar effect elsewhere in Europe and Africa. By late July it had also driven an increase in daily infections in parts of Asia, the United States and Australia.
As of 20 July 2021, this variant had spread to 124 countries, and WHO had indicated that it was becoming the dominant strain, if not one already.
[Read more on the Delta variant at Wikipedia.]