Study By Delhi Private Hospital Shows How Crucial Two Doses Of Vaccines Are Against Covid-19
A study by a private hospital in Delhi during peak of the second wave of Covid-19 has shown that single dose of vaccination may be not enough to protect against symptomatic infections, highlighting the need to improve coverage of fully vaccinated individuals in India.
Vaccine effectiveness for a single dose of Covishield against symptomatic infections was at 18%, the study by Sir Ganga Ram Hospital, published in the European Journal of Internal Medicine, said. The single dose, however, was 69% effective in preventing death and 53% against the need for oxygen therapy.
“In countries facing acute vaccine shortages, administrators could consider early full vaccine coverage, prioritising those never infected, before the onset of another SARS-CoV-2 outbreak,” the authors of the study said. “Relying on the protective effect of a single dose alone may not be prudent.”
That assumes significance in India which has only been able to fully vaccinated 13% of its targeted adult population so far. While the country has administered more than 55.3 crore vaccine shots, the number of individuals with two jabs is 12.23 crore.
The study — conducted between March and May, led by Dr. Ruma Satwik — covered 4,266 individuals. The participants were vaccinated between January and April. Of the total number of individuals, 2,716 received two doses, and 623 received a single jab of Covishield, 927 remained unvaccinated.
Findings on lower vaccine effectiveness from a single-dose has similarities to a larger study funded by the U.K. government. It found that a single dose was 30% effective against the more infectious Delta variant of the virus. The effectiveness rose to 67% for two shots. Another separate study by Public Health Scotland reported lower effectiveness (25-60%) against the Delta variant.
Getting two jabs significantly improved the vaccine effectiveness, particularly when it came to deaths, the Sir Ganga Ram Hospital study showed. For symptomatic infections, vaccine effectiveness of Covishield given at a median interval of 30 days was found to be 28%. A higher 76% protection was seen against supplemental oxygen therapy, while the jabs were 97% effective in preventing deaths.
Another key finding of the study was that previous Covid-19 infections offered significant protection too. An effectiveness of 93% was seen against symptomatic infections, 89% against moderate to severe disease and 85% against supplemental oxygen therapy. However, it does not specify how long this protection lasts.