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A new Indian study suggests that the inactivated whole virus vaccine Covaxin made in India against severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) retains significant efficacy against new delta variants of the virus. These preliminary results come after both variants showed some resistance to antibody-mediated neutralization caused by the first generation Pfizer or AstraZeneca coronavirus (COVID-19) vaccines.
A pre-printed version of the study is available on the website bioRxiv* server, while the article is subject to peer review.
context
COVID-19, caused by the new pathogen SARS-CoV-2, has caused immense disruption as governments and public health authorities attempt to tame it through social distancing, travel bans, blockades and the vaccination. The unprecedented development of vaccines and their rapid approval for emergency use has led to the distribution of more than 600 million doses worldwide, mainly in the first world.
However, the efficacy of the vaccine is threatened by the emergence of new strains with mutations in the peak region which interact with the host cell receptor to accomplish infection and viral entry. One of these is the delta variant, a worrying variant of SARS-CoV-2 (VOC) – also known as the B.1.617.2 variant.
First detected in India, it has since been sequenced in many countries, where it has become the dominant strain, passing the sublines Kappa (B.1.617.1) and B.1.617.3, as well as the more older alpha, beta and gamma variants.
Recent research indicates that this VOC has the potential to be neutralized by Pfizer BNT162b2, AstraZeneca Covishield and BBV152 / Covaxin vaccines, the latter two being used in India. Nonetheless, the fact remains that the delta variant is responsible for the majority of breakthrough infections worldwide.
India’s vaccine, BBV152, based on an inactivated whole virion platform, has successfully passed preclinical and early clinical trials and is being used for mass vaccination in the country.
The double-blind, randomized, multicenter, phase 3 clinical trial of this vaccine indicated a vaccine efficacy of 65% in terms of protection against the delta variant. Since then, however, other mutations have led to the emergence of Delta AY.1, AY.2 and AY.3.
The AY.1 mutant was also first identified in India, in April 2021, but has now appeared in around 20 other countries. He was reported to have the potential for immune evasion. The K417N mutation in the spike protein could also confer resistance to the monoclonal antibodies Casirivimab and Imdevimab.
Researchers are looking to determine its transmissibility, disease severity and immune escape characteristics. There is little information on its clinical profile in vaccinated individuals.
Objectives of the study
The present study evaluated the titer of the vaccine-induced immune antibody isotype immunoglobulin G (IgG) in three test situations.
The researchers looked at the levels of IgG and neutralizing antibodies in three cohorts of subjects. The first included 40 COVID-19 naive subjects who had been fully vaccinated, with samples obtained 2.5 to 22 weeks from the second dose.
The second included 20 previously infected subjects who had recovered and received a full course of vaccine, collected 14 to 70 weeks after the second dose. The third was made up of those who had developed breakthrough infections with SARS-CoV-2 after being fully vaccinated, with samples taken at 12-18 weeks from the second dose.
The vaccine used in all cases was BBV152. The geometric mean titer (GMT) of neutralizing antibodies varied between 200 and 300 for strains B.1, delta and AY.1, but only 165 against B.1.617.3. In the post-COVID-19 vaccinated cohort, it was double or more for B.1, at around 800 versus 300 in the naive cohort, but otherwise comparable to those in the first group.
The highest titres were in the breakthrough infection group, around 900 versus B.1 and 470, 300 and 260 versus the other three variants, respectively.
What were the conclusions?
Scientists found that neutralizing activity was induced at significantly higher levels by a natural infection associated with vaccination, whether the first occurred before or after vaccination. This was confirmed by enzyme-linked immunosorbent assay (ELISA) which showed titers 2.7 to 4 times higher in the revolutionary cohort compared to the naive vaccinated cohort when tested for the S1 viral peak. , the receptor binding domain (RBD) and the nucleoprotein.
This may indicate the essential role of immune memory cells in strengthening the immune response.
Neutralizing activity was slightly reduced, up to 2-fold, for Delta, Delta AY.1 and B.1.617.3, compared to variant B.1, after complete vaccination in naïve individuals. The reduction was greater in the other cohorts, up to four times with COVID post-vaccination cases, and 3 to 5 times in the third cohort.
With the ChAdOx1 and BNT162b2 vaccines, two doses resulted in four-fold and 11-fold lower neutralizing titers against the delta variant, as reported in other studies. This has also been observed with BBV152 and Covishield.
Nevertheless, the researchers observe: “With the high titers observed, sera from individuals belonging to all the aforementioned groups would still effectively neutralize the Delta, Delta AY.1 and B.1.617.3 variants.. “
*Important Notice
bioRxiv publishes preliminary scientific reports which are not peer reviewed and, therefore, should not be considered conclusive, guide clinical practice / health-related behavior, or treated as established information.
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