NEW DELHI: The genomic analysis of breakthrough infections in healthcare workers has shown that the Covishield vaccine is effective in preventing severe COVID-19, says a study by Indian genomic experts.
The study Genomic survey of SARS-CoV-2 vaccine breakthrough infections in healthcare workers from Kerala published in the Journal of Infection, highlights the importance of continued genomic surveillance for tracking emergent SARS-CoV-2 variants.
This work was supported by the National Health Mission Kerala as part of the genomic surveillance and the Council of Scientific and Industrial Research (CSIR), India.
All six patients in the study were vaccinated at an interdose interval range of 4-6 weeks and COVID-19 symptoms were observed in all at least 15 days post the second dose.
Considering the efficacy of Covishield against symptomatic COVID-19 following two standard doses is 63 per cent, a small percentage of fully-vaccinated people may still get infected. However, it is important to note that none of the six patients presented with severe illness or required hospitalization, the study noted.
Characterization of clinically important SARS-CoV-2 variants in vaccinated individuals confers possible exploration of a selection of viral escape mutants following immunization.
"Genome sequencing revealed that 4 patients in this study were infected by the B.1.1.7 variant of SARS-CoV-2. N501Y, a key mutation in the B.1.1.7 lineage has been reported to escape neutralization by some monoclonal antibodies (mAbs), and a small decrease in neutralization activity in patients vaccinated with Moderna (mRNA-1273) or Pfizer–BioNTech (BNT162b2) [[10]]," it said.
B.1.1.7 has also been shown to lower neutralising antibody titres against vaccines as compared to non-B.1.1.7 variants.
"Both E484K and S477N, found in two patients, are reported to escape neutralization by a range of mAbs. E484K is also associated with a decrease in neutralizing activity of convalescent and post-vaccination sera," it further said.
The experts concluded that while it remains unclear if these breakthrough infections are related to vaccine efficacy, immune evasion, or other factors, the study highlights the importance of continued genomic surveillance for tracking emergent SARS-CoV-2 variants.