Scientists from the Pune-based National Institute of Virology (NIV) conducted the largest study done so far in India to understand why people got Covid-19 despite taking one or two vaccine shots.
The genomic analysis carried out as part of the study showed the Delta variant’s presence in the majority of the samples, but there also were other variants such as Alpha, Kappa, Delta AY.1 (known as the Delta-plus variant in samples from MP and Rajasthan) and Delta AY.2.
The occurrence of Covid in vaccinated people is called a ‘breakthrough infection.’ The NIV study, which is in the preprint stage of publication, proves that the Delta variant — first isolated in Vidarbha in October 2020 and now acknowledged as the cause for the massive second wave — caused breakthrough infections.
“At the moment, the Delta variant is causing infections throughout the world, but the most important point of our study is that vaccination offers more than 99% protection against death even in the presence of the highly transmissible and more virulent Delta strain,” said Dr Yadav.
While 53 samples for the study, conducted between March and June, were collected from Maharashtra, the highest number was 181 from Karnataka and the lowest number was 10, from West Bengal. Genetic sequencing was performed on each positive sample to find the Delta variant.
“This study indicated that a majority of the clinical cases in the breakthrough were infected with the Delta variant and only 9.8% cases required hospitalization, while fatality was observed in only 0.4% cases. This clearly suggests that the vaccination does provide reduction in hospital admission and mortality,” concluded the study.
Most patients in this study were young — the median age was 44 (31-56), more were men (65.1%) and 71% of them were symptomatic, with one or more symptoms. Fever (69%) was the most common symptom, followed by bodyache, including headache and nausea (56%), cough (45%) and sore throat (37%).
The researchers said breakthrough Covid-19 infections have been reported from various countries. “It appears the current Covid-19 vaccines are disease-modifying in nature wherein mild or less severe infections are expected to occur in vaccinated individuals,” said the study. Vaccination prevents severe disease, hospitalization and death, as is being seen in the UK, Israel and Canada.
The NIV doctors who carried out the study said that the continuous monitoring of breakthrough infections is important. “Such monitoring will help us to understand the need to adequately tweak the available vaccines and also develop new vaccines with enhanced potential to protect against variant strains of SARS-CoV-2,” said Dr Yadav.