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COVID 19 - Delta and Delta Plus Variant

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 the substitutions T478K, P681R and L452R, which are known to affect the 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.

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 B.1.1.7 (Alpha variant); the UK's SAGE 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. The variant is thought to be partly responsible for India's second wave of 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.

"Delta plus" variant

Delta with K417N corresponds to lineages AY.1 and AY.2 and has been nicknamed "Delta plus" or "Nepal variant". It has the K417N mutation which is also present in the Beta variant.  The exchange at position 417 is a lysine-to-asparagine substitution.

As of 15 July 2021, the AY.3 variant accounted for approximately 21% of cases in the United States.

UK scientists have said that the Delta variant is between 40% and 60% more transmissible than the previously dominant Alpha variant, which was first identified in the UK (as the Kent variant). Given that Alpha is already 150% as transmissible compared to the original Wuhan strain, and if Delta is 150% as transmissible compared to Alpha, then Delta maybe 225% as transmissible compared to the original strain. BBC reported that {\displaystyle R_{0}}R_{0} – basic reproduction number or the expected number of cases directly generated by one case in a population where all individuals are susceptible to infection – for the original Wuhan virus to be 2.4-2.6, for Alpha 4-5, and for Delta 5-8; these can be compared to seasonal influenza (1.2-1.4), common cold (2-3), smallpox (3.5-6), and chickenpox (10-12).

Surveillance data from the Indian government's Integrated Disease Surveillance Programme (IDSP) shows that around 32% of patients, both hospitalised and outside hospitals, were aged below 30 in the second wave compared to 31% during the first wave, among people aged 30–40 the infection rate stayed at 21%. Hospitalisation in the 20-39 bracket increased to 25.5% from 23.7% while the 0-19 range increased to 5.8% from 4.2%. The data also showed a higher proportion of asymptomatic patients were admitted during the second wave, with more complaints of breathlessness.

Surveillance data from the U.S., Germany and the Netherlands indicates the Delta variant is growing by about a factor of 4 every two weeks with respect to the Alpha variant.

In India, the United Kingdom, Portugal, Russia, Mexico, Australia, Indonesia, Russia, South Africa, Germany, Luxembourg, the United States, the Netherlands, Denmark, France and probably many other countries the Delta variant had become the dominant strain by July 2021. There is typically a three-week lag between cases and variant reporting.

On 7 June 2021, researchers at the National Centre for Infectious Diseases in Singapore posted a paper suggesting that patients testing positive for Delta are more likely to develop pneumonia and/or require oxygen than patients with wild type or Alpha.

On June 14, researchers from Public Health Scotland found that the risk of hospitalization from Delta was roughly double that of from Alpha.

On June 11, Public Health England released a report finding that there was a "significantly increased risk of hospitalization" from Delta as compared with Alpha.

On July 9, Public Health England reported that the Delta variant in England had a case fatality rate (CFR) of 0.2%, while the Alpha variant's case fatality rate was 1.9%, although the report warns that "case fatality rates are not comparable across variants as they have peaked at different points in the pandemic, and so vary in background hospital pressure, vaccination availability and rates and case profiles, treatment options, and impact of a reporting delay, among other factors. "James McCreadie, a spokesperson for Public Health England, clarified "It is too early to assess the case fatality ratio compared to other variants."

On 12 July, a preprint study from epidemiologists at the University of Toronto, Canada found that Delta had a 120% greater risk of hospitalization, 287% greater risk of ICU admission and 137% greater risk of death compared to non-variant of concern strains of SARS-COV-2.


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