An Indian Council of Medical Research (ICMR) study conducted in Chennai has found that the Delta variant of the Covid-19 virus has the potential to infect both vaccinated and unvaccinated people, but it reduces mortality among the former group.
The study was approved by the Institutional Ethics Committee of ICMR-National Institute of Epidemiology, Chennai and published in the Journal of Infection on August 17.
The study findings indicate that the prevalence of the Delta variant or B.1.617.2 was not different between the vaccinated and unvaccinated groups. The high transmissible Delta variant is the dominant strain circulating across the world and is one of the primary drivers for the second wave of SARS-CoV-2 in India.
The report quoted other studies that have documented a reduction in neutralisation titres among Covishield and Covaxin vaccine recipients after infection with the Delta variant. “This might be the reason for the breakthrough infections observed in the fully vaccinated individuals,” the published paper said.
Jeromie Thangaraj, a scientist at the National Institute of Epidemiology who was involved in the study said that since the sample size was low, they did not include re-infections as it was very few and have not further classified whether those who were infected post-vaccination had taken Covishield or Covaxin. “But the proportion of patients progressing to severe illness and mortality was lower in the vaccinated group which is the case globally,” said Jeromie.
The proportion of patients with moderate and severe illness was significantly lower in the fully vaccinated group than in the unvaccinated group. “No deaths were reported in the fully vaccinated group, whereas three partially vaccinated (patients) and seven unvaccinated patients died,” the report said.
After completing the study in May, the data was shared with Tamil Nadu’s health department. The report suggested that non-pharmaceutical interventions must continue to slow down the transmission combined with speedy vaccination coverage.
Chennai was one of the worst affected cities during the second wave of Covid-19 in India with nearly 6000 cases reported daily during the first three weeks of May 2021, despite a high seroprevalence of around 45% estimated during October-November 2020. The study group selected patients from three triaging centres in the city.
Of the 3,790 people who visited the triage centres between the first week of May, 373 reported receiving at least one dose of vaccine 14 days prior to their Covid-19 positive diagnosis. The remaining 3,417 were unvaccinated. The study enrolled 354 (94.9%) of the 373 in the vaccinated group. Of this 241 people had taken one dose or were partially vaccinated and 113 had taken two doses or were fully vaccinated. As many as 185 (5.4%) of the 3417 unvaccinated individuals were included in the study. The median age of the individuals who were unvaccinated, partially vaccinated and fully vaccinated were 47 years, 53 years and 54 years respectively.
After retrieving genomic sequences from 414 of the 539 samples it was found that the delta variant was the predominant variant of concern in Chennai. About 72.4% in the unvaccinated group and 68% and 74% among the partially and fully vaccinated groups were found. Among the fully vaccinated, a majority that is 85% had IgG antibodies against SARS-CoV-2 whereas 63.9% were partially vaccinated and 14.6% in the unvaccinated group were seropositive. “We also found the delta plus variant in five participants,” said Thangaraj. One out of the five infected with delta plus (AY.1) required hospitalisation with oxygen support but the rest had mild disease.
Dr K Kolandaswamy, the former director of the directorate of public health in Tamil Nadu said that the objective for vaccination is threefold prevention: from infection, from the severity of disease and mortality.
“The study isn’t able to measure how much prevention from infection has been achieved but it does clearly indicate that the other two objectives are working,” Kolandaswamy said.
“And it shows with evidence what we have been repeatedly saying that no matter what variant is in transmission, we have to continue with Covid-19 appropriate behaviour like masking, hand washing social distancing and increase vaccine coverage,” he added.