Single dose of vaccine can’t control Delta Variant: Global Study on vaccines

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The data from clinical trials and post-vaccination study on vaccines shows that the Dominant delta variant of Covid-19 can’t be easily controlled by a single dose of vaccine. The countries must administer two doses of vaccine and should reduce the time gap between them.

  • The WHO has recently given a new classification to SARS-CoV-2 variants of interest (VOI) and variants of concern (VOC) on the basis of Greek letters. The objective was to create easy-to-pronounce and non-stigmatising labels for VOI and VOC.
  • However, the established nomenclature systems for naming and tracking of SARS-CoV-2 genetic lineages by GISAID, Nextstrain and Pango will remain in use for scientific research.
  • The new classification is as follows:
    • VOC B.1.1.7 will be called Alpha Variant. It was the earliest documented in the United Kingdom (September 2020).
    • VOC B.1.351 will be called Beta Variant. It was the earliest documented in South Africa (May 2020).
    • VOC P.1 will be called Gamma Variant. It was the earliest documented in Brazil (November 2020).
    • VOC B.1.617.2 will be called Delta Variant. It was the earliest documented in India (October 2020).
About the Delta Variant:
  • It was first identified in Maharashtra and is believed to be responsible for the severe second wave in India.
  • It has now spread to most parts of India and also been identified in many other countries.
  • The rapid expansion has induced the WHO to graduate it from a “variant of interest” (VOI) to a “variant of concern” (VOC) category.

Scientists have undertaken various studies to address 3 major questions surrounding the delta VOC – 

  1. Is it more infectious than the prevalent virus?
  2. Is it more lethal than the previous virus?
  3. Does the delta variant is more resistant to the effect of vaccines? 
Data shown by various studies on vaccines:

Read Also :-What are “Variants of Concern” (VoC)?

  • Results of Study conducted by Indian SARS-CoV-2 Genomic Consortia (INSACOG) and the National Centre for Disease Control (NCDC):
    • The Delta variant is the “prime reason” behind the second wave, though the wave may have been initiated by the Alpha variant.
    • The Delta Variant has become dominant even in Britain, where scientists have recently noted that it is 50% more infectious than the Alpha variant.
  • Results of study on vaccines conducted by Public Health England:
    • A single dose of the AstraZeneca vaccine provided 33% efficacy against the Delta variant, while it was 51% against the Alpha variant.
    • The second dose improved the efficacy to 60% against the Delta variant and to 66% against the Alpha variant.
    • Further, two doses of Pfizer-BioNtech vaccine provided much higher levels of protection than two doses of the AstraZeneca vaccine.
  • Results of a British study on vaccines published in Lancet Journal:
    • Merely 32%of the vaccinated individuals had adequate antibody levels against the Delta variant after the first dose of the Pfizer vaccine. It was 25% against the beta variant.
    • The antibody levels rose after the second dose. However, they were far below the levels obtained against the initial variant of the Covid-19 virus.
  • Results of a study on vaccines conducted by the Pasteur Institute, France:
    • The Delta variant showed reduced response to both the vaccines (Pfizer and Astrazeneca). It was resistant to neutralisation by some monoclonal antibodies targeting the Spike protein.
    • The study concluded that a single dose of the Astrazeneca vaccine will not display optimal protection against the delta variant.

Lessons learnt from the various study on vaccines:

  • First, the Delta variant is the most infectious variant in circulation. However, there is not much convincing evidence to prove it is more deadlier than the previous variants.
  • Second, vaccines have diminished efficacy against the delta variant. Further, a single dose of either the AstraZeneca or the Pfizer-BioNTech vaccine does not provide adequate protection against the Delta variant.
  • Third, a shortened dosing interval is recommended to deal with the Delta variant. Britain has already reduced the interval to 8 weeks from earlier 12 weeks.

Source: The Indian Express

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