There has been a rapid increase in the delta variant of SARS CoV-2 in France in June 2021 based on the analysis of 5061 positive samples1. The next few weeks are very crucial with respect to the emergence of the third wave due to higher transmissibility of the delta variant and the impact it will have on the public and private healthcare system. The mortality and morbidity to be associated with the third wave will depend on the effectiveness of the AstraZeneca ChAdOx1 vaccine, to the delta variant, that have been administered to the population.
Analysis of the UK population that has received the first and second dose of the ChAdOx1 vaccine reveals that the after the first dose, the vaccine was less effective (33.5% against the B.1.617.2 [delta variant] as compared to 51.1% against the B.1.1.7 variant)2. In addition, after the second dose also, the vaccine was less effective (59.8% against the B.1.617.2 [delta variant] as compared to 66.1% against the B.1.1.7 variant)2.
Why are we seeing different waves of COVID-19 in various countries at different times? The answer may lie in the fact that the herd immunity has not yet reached and the “lock-down” has been removed leading to the next wave of COVID-19. The “lock-down” in fact prevents the transmission of the virus and thereby prevents viral replication and mutation. However, the challenge faced is the fact that each time a wave comes, the virus gets a chance to mutate which may result in a more transmissible variant (form of the virus that has greater infectivity resulting adhering to the survival of the fittest theory), thus negating the effect of herd immunity reached against the previous variant of the virus. Recently, a new variant called the delta plus variant has emerged that combines the delta variant with the K417N mutation (first found in the Beta variant that emerged in South Africa). This delta plus variant is resistant to antibody therapy treatments. All this poses a difficult challenge in terms of attaining herd immunity.
Herd immunity3 may still be reached if the vaccines being administered provide a significant protection of at least greater than 90% as claimed by the mRNA vaccines of Pfizer and Moderna (93.4% with 2 doses of Pfizer against the B.1.1.7 variant and 87.9% against the B.1.617.2 [delta variant]). However, these vaccines are being administered majorly in the USA and the UK, while others countries are mainly dependent on the ChAdOx1 (AstraZeneca) vaccine, the Russian Sputnik V vaccine and the Indian Covaxin vaccine. These vaccines may or may not provide effective immunity against the newly generated variants. In the absence of effective vaccines and the fact that new highly transmissible strains are being generated nearly every time virus replicates leading to mutation, it may take several months to reach the relevant herd immunity and the next waves of COVID-19 will continue till effective herd immunity is achieved.
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References
- Alizon S., Haim-Boukobza S., et al 2021. Rapid spread of the SARS-CoV-2 δ variant in the area of Paris (France) in June 2021. Posted June 20, 2021 in Preprint medRxiv. DOI: https://doi.org/10.1101/2021.06.16.21259052
- Bernal J L, Andrews N, Gower C et al. Effectiveness of COVID-19 vaccines against the B.1.617.2 variant. Posted May 24, 2021. DOI: https://doi.org/10.1101/2021.05.22.21257658
- Soni R 2021. COVID-19: An Evaluation of Herd Immunity and Vaccine Protection. Available online at http://scientificeuropean.co.uk/covid-19/covid-19-an-evaluation-of-herd-immunity-and-vaccine-protection/
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