Single dose of Covishield offers no shield against symptomatic infection: Study

New Delhi: A study by Sir Ganga Ram Hospital in Delhi conducted amid the peak of the second wave of Covid-19 has noted that single dose of Covishield vaccine may not provide enough protection against symptomatic infections, highlighting the need to improve coverage of full dose vaccination among the individuals.
The researchers noted that the incidence of symptomatic infection among the study subjects, after 21 days of receiving the first dose of Covishield, was 12.3%, as compared to 13.9% in the unvaccinated group.
However, the single dose was found 69% effective in preventing death and 53% against the need for oxygen therapy.
Published in the European Journal of Internal Medicine, the study was conducted between March and May over 4,276 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.
The outcome was based on 560 Covid-19 infections detected among them between March and May this year and 50 per cent of the cases accounted for Delta variant.
The study also showed that getting two doses of Covishield significantly improved the vaccine effectiveness. For symptomatic infections, vaccine effectiveness 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.
However, vaccine effectiveness for 2 doses given at a median interval of 30 days increased to 28% for symptomatic infections, 67% for moderate to severe disease, 76% for supplemental-oxygen-therapy & 97% for deaths.
Another noteworthy finding is that previous Covid-19 infections offered significant protection against all studied outcomes. “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,” the study said.
The researchers outlined that relying on the protective effect of a single dose alone may not be prudent and full vaccination should be prioritised before the arrival of the third wave of the Covid-19.
“In countries facing acute vaccine shortages, administrators could consider early full vaccine coverage, prioritizing those never infected,” they suggested in the study.
UNI