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Efficacy of vaccines against symptomatic diseases caused by variants of Omicron and Delta in the United Kingdom




The rapid and relentless spread of the 2019 coronavirus disease (COVID-19) pandemic elicits a safe and effective vaccine against the causative agent, coronavirus 2 (SARS-CoV-2). It led to an intensive research effort for.This culminated in the deployment of several vaccines built on Nucleic acidThe entire inactivated virus, and the viral vector platform, all high Effectiveness Against variants of the ancestors of the virus.

study: Efficacy of Covid-19 vaccine against Omicron (B.1.1.529) variant.. Image Credit:

However, the emergence of many new variants with varying degrees of antigenic escape, coupled with significant vaccine hesitation, has challenged most national and international health authorities and government goals to end the pandemic. New studies report recent findings on the efficacy of these vaccines against the Omicron (B.1.1.529) mutant of SARS-CoV-2.


Cases of COVID-19 have occurred in many different countries, despite the deployment of highly effective vaccines at doses of 2, 3 or higher, such as Pfizer and Moderna’s messenger ribonucleic acid (mRNA) vaccines. It is increasing rapidly. This led to questions about the actual efficacy of vaccines in the face of increasingly widespread antigenic escape variants such as Omicron.This variant has the highest number of mutations reported so far among all mutants, including many of the dominant spikes. antigenReceptor binding domain (RBD).

Omicron cases first showed an increase in late November in the UK, with more than 60% of patients over the age of 20 receiving either BNT162b2 (Comirnaty, Pfizer–BioNTech) or ChAdOx1 nCoV-19 (Vaxzevria, AstraZeneca). It has been administered twice. , Or the mRNA-1273 (Spikevax, Moderna) vaccine. Of those over the age of 50, more than 80% received two doses.

Booster administration was started 6 months after the first course, but was later reduced to 3 months when faced with the rapid spread of the Omicron mutant.

In the current study New England Journal of MedicineThe researchers aimed to estimate how effective vaccination was against severe COVID-19 caused by the Omicron and Delta variants of the virus in the United Kingdom. All participants received a primary course of the mRNA vaccine BNT162b2 or mRNA-1273, or the viral vector vaccine ChAdOx1 nCoV-19, and boost immunization of the BNT162b2, ChAdOx1 nCoV-19, or mRNA-1273.

Vaccine efficacy for symptomatic disease was calculated after 1) primary course and 2) booster immunization.

What did the study show?

The study period was extended from 27 November 2021 to 12 January 2022, with more than 885,000 Omicron infected, more than 200,000 Delta infected, and more than 1.5 million virus negative.

The findings showed that the vaccine was much more effective against delta than the Omicron variant, regardless of the time of evaluation or the exact combination of vaccines used.

Interestingly, the ChAdOx1 nCoV-19 vaccine showed no protective effect against symptomatic disease by Omicron after the second dose when evaluated 5 months after the second dose. Conversely, two BNT162b2 doses protected against symptomatic treatment for about a month, reducing risk by 66% in 2-4 weeks, but less than 10% in 6 months and above.

By comparison, two doses of this vaccine prevented 83% of cases with delta symptoms in 2-4 weeks and 44% after 6 months.

For those who received the BNT162b2 booster following the first course of the ChAdOx1 nCoV-19 vaccine, the immediate efficacy of Omicron for symptomatic disease (within 1 month of booster administration) was 62%. The corresponding risk reduction was 70% using the mRNA-1273 booster in 2-4 weeks. However, in 10 weeks, BNT162b2 and mRNA-1273 boosters prevented 40% and 60% of symptomatic cases of Omicron compared to similar unvaccinated cases.

In patients who received two doses of the BNT162b2 vaccine and a third booster allogeneic, the risk of symptomatic disease was reduced by 67% in 2-4 weeks, but the risk was halved in 10 weeks and above. When the mRNA-1273 booster was used instead, symptomatic cases decreased by 74% in 2-4 weeks and 64% in 5-9 weeks.

The main course of the mRNA vaccine against Delta was in all respects more defensive than the ChAdOx1nCoV-19 vaccine. Regardless of the primary course, the mRNA booster initially provided over 95% protection against Delta, which remained high for over 10 weeks.

What is the impact?

The results of this comprehensive vaccine study show that double doses of the ChAdOx1 nCoV-19 or BNT162b2 vaccine are symptomatic COVIDs caused by Omicron compared to useful protective immunity induced against delta symptomatic disease. It shows that it was not very useful in defending from 19. A third dose of either mRNA vaccine improved short-term protection, but this immunity declined rapidly.

With far fewer hospitalizations caused by Omicron during the study, it was difficult to estimate the protection provided by the vaccine against severe and deadly COVID-19. At Delta, the vaccine provided lasting protection against the serious consequences of COVID-19.

Therefore, this study found that after the primary course of BNT162b2, when faced with Omicron against ancestral mutants, the neutralizing activity was reduced by 20-40 fold, at least 10 fold when Omicron was compared to the Delta mutant. It supports previous studies showing that it does. This reduction is even higher after the first course of ChAdOx1 nCoV-19 vaccination, and many serum samples show undetectable neutralizing activity against Omicron before the booster dose is administered.

The poor response of the ChAdOx1 nCoV-19 vaccine in the primary course is due to the longest gap between primary vaccination and exposure to Omicron variants due to the earliest administration of this vaccine, with correspondingly lowest immune levels. It needs to be interpreted with that in mind. Second, although it was administered to the highest-risk group, the mRNA vaccine is the predominant vaccine used in younger populations and was deployed in the United Kingdom later in the pandemic.

Despite these apparently disappointing discoveries, scientists claim:Based on the experience of other variants and early estimates of hospitalization rates, vaccine efficacy for severe illness may be significantly higher than estimates for symptomatic treatment... “Further investigation is needed to verify this claim.




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