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The Delta variant (B.1.617.2) was [3] [4] a variant of SARS-CoV-2, the virus that causes COVID-19. It was first detected in India on 5 October 2020. It was first detected in India on 5 October 2020. The Delta variant was named on 31 May 2021 and had spread to over 179 countries by 22 November 2021.
In August 2021, results from a study suggested that the effectiveness against infection decreased from 91% (81 – 96%) to 66% (26 – 84%) when the Delta variant became predominant in the US, which may be due to unmeasured and residual confounding related to a decline in vaccine effectiveness over time.
The potential emergence of a SARS-CoV-2 variant that is moderately or fully resistant to the antibody response elicited by the COVID-19 vaccines may necessitate modification of the vaccines. [336] The emergence of vaccine-resistant variants is more likely in a highly vaccinated population with uncontrolled transmission.
Evidence from vaccine use during the pandemic shows vaccination can reduce infection and is most effective at preventing severe COVID-19 symptoms and death, but is less good at preventing mild COVID-19. Efficacy wanes over time but can be maintained with boosters. [398]
ZF2001, trade-named Zifivax or ZF-UZ-VAC-2001, is an adjuvanted protein subunit COVID-19 vaccine developed by Anhui Zhifei Longcom in collaboration with the Institute of Microbiology at the Chinese Academy of Sciences.
A test-negative [note 1] case-control study published in August 2021, found that two doses of the BNT162b2 (Pfizer) vaccine had 93.7% effectiveness against symptomatic disease caused by the alpha (B.1.1.7) variant and 88.0% effectiveness against symptomatic disease caused by the delta (B.1.617.2) variant. [87]
The mRNA vaccine from Pfizer and BioNTech may be less effective than Moderna's against the Delta variant of the coronavirus, according to two reports posted on medRxiv on Sunday ahead of peer review.
JERUSALEM (Reuters) -The Pfizer-BioNTech >PFE.N< vaccine is highly effective against the Delta variant of COVID-19, a Pfizer official in Israel said on Thursday. First identified in India, Delta ...