Delta variant not different between vaccinated and unvaccinated: Study

Prevalence of B.1.617.2 variant of Covid-19, widely known as Delta variant, was not “different between” the vaccinated and unvaccinated individuals in Chennai, a study conducted by Indian Council for Medical Research (ICMR) has concluded.

The study, approved by the National Institute of Epidemiology, Chennai of the ICMR, was conducted among both vaccinated and unvaccinated individuals who visited triaging centres of the Greater Chennai Corporation (GCC) between May 3 and 7, when the second wave of Covid-19 was vociferous in the city and elsewhere in Tamil Nadu.

“The study findings indicate that the prevalence of B.1.617.2 was not different between the vaccinated and unvaccinated groups. Delta variant was the dominant circulating strain and one of the primary drivers for the second wave of SARS-CoV-2 in India,” the study said.

The study concluded that B.1.617.2 has the potential to infect both vaccinated and unvaccinated individuals. However, it said, the progression of illness seems to be prevented by vaccination.

“Therefore, non-pharmaceutical interventions must continue to slow down the transmission. Additionally, the pace and scale of vaccination have to be increased to mitigate the further waves of the pandemic,” the study added.

The study chose three triaging centres in the north, central, and southern parts of the city and enrolled consenting Covid-19 positive individuals visiting these centres who had taken at least one dose of Covid-19 vaccine a fortnight before confirmation of the diagnosis.

The institute also recruited unvaccinated Covid-19 positive individuals for the study and collected demographic details, clinical history, comorbidities, previous Covid-19 history and the date of vaccination.

“Nasal and oropharyngeal (N/OP) swabs and blood samples were collected from the study participants. We tested the N/OP swab samples for the detection of E and RdRP gene using Real-time RT-PCR and only those with Ct<30 were included for the preparation of RNA libraries Illumina Covidseq protocol (Illumina Inc, USA),” the study said.

The participants were followed up telephonically after four weeks to collect information about their symptoms, hospitalisation and treatment details, and clinical outcome.

“Patients with SpO2 < 94%, dyspnoea and requiring supplemental oxygen during hospitalization were considered as having moderate/severe illness and remaining as mild illness. Categorical variables were expressed as proportions and continuous variables as the median and interquartile range (IQR),” the study said.

Of the 3,790 Covid-19 cases who visited the triage centres between May 3 and May 7, 2021, 373 reported receiving at least one dose of vaccine 14 days before their Covid-19 diagnosis and the remaining 3,417 were unvaccinated. The study enrolled 354 (94.9%) of the 373 vaccinated and 185 (5.4%) of the 3,417 unvaccinated individuals.

“Studies have documented reduction in neutralization titres among Covishield and Covaxin recipients after infection with delta variant. This might be the reason for the breakthrough infections observed in fully vaccinated individuals. However, the proportion of patients progressing to severe illness and mortality was lower in the vaccinated group,” the study said.