NEW DELHI: Among those fully vaccinated, the rate of breakthrough infections of Covid-19 was found to be 1.6 % in the largest such study from India so far while another one by top government agencies has found the B.1617.2 variant to be causing a large number of such cases in Delhi.
A person is considered fully vaccinated two weeks after the second dose of the vaccine is administered.
The study had been carried out at the Post Graduate Institute of Medical Science and Research, Chandigarh and has been published in the prestigious The New England journal of Medicine. It followed 12,248 health care workers, 7170 of whom had received the first dose of vaccine, with 3650 subsequently receiving the second dose.
A total of 5078 health care workers were unvaccinated while the rest had all received Covishield.
The researchers found that a total of 184 of the 7170 health care workers (2.6%) tested positive after receiving at least one dose of vaccine and the median time between receipt of the first dose and the positive test was 44 days.
A total of 72 of the 3650 health care workers (2 %) on the other hand tested positive after the second dose and the median time from receipt of the second dose to the positive test was 20 days.
Among the health care workers who received both doses and completed at least 14 days of follow-up after the second dose, the incidence of breakthrough infection was 1.6% (48 of the 3000 health care workers) and the median time from receipt of the second dose to breakthrough infection was 29.5 days.
These findings come soon after cases of 47 breakthrough infections -- at a rate of 0.5 % -- were reported from a hospital in the US among healthcare workers who were fully vaccinated with Covid-19 vaccines either by Pfizer-BioNTech or Moderna.
Back home, in a separate scientific research carried out by the National Centre for Disease Control, Delhi, CSIR Institute of Genomics and Integrative Biology and the Academy for Scientific and Innovative Research in the national capital to understand the Covid-19 second wave genomically, a total of 27 cases of breakthrough infections were seen.
Among these cases, B.617.1 lineage was seen in 8 % of the breakthrough infections and a whopping 76 % cases were caused by B.1.617.2 -- the variant now considered far more transmissible and capable of evading immunity than other variants of the Covid virus.
"It is noted that when compared to population prevalence, B.1.617.2 was over-represented and B.1.1.7 was not even detected in vaccination breakthroughs, suggesting a higher breakthrough risk of B.1.617.2 compared to B.1.1.7," the researchers noted in their paper Genomic characterization and Epidemiology of an emerging SARS-CoV-2 variant in Delhi, India.
Despite a Covid19 vaccination drive underway in India with two vaccines -- Covishield and Covaxin --there have been some concerns against their potential to protect people from Covid-19, especially in the wake of new variants of the virus in circulation.
ALSO WATCH :