Seventy per cent of the people who received a booster dose of the Covid vaccine did not contract the disease during the third wave, according to a new study that covered nearly 6,000 people in India.
The study led by Dr Rajeev Jayadevan, co-chairman of the Indian Medical Association's national task force on coronavirus, said that 45 per cent of the people who did not take a precautionary dose reported Covid in the third wave.
The survey covered 5,971 vaccinated people, of which 24 per cent were aged below 40 and 50 per cent belonged to the 40-59 age group. Women accounted for 45 per cent of the people surveyed, while 53 per cent were healthcare workers.
A total of 3,361 people reported getting infected at least once. Of these, 2,311 (70 per cent) had Covid during the third wave, it said.
"Of the 5,971 people, 2,383 took the booster dose and 30 per cent of them reported Covid during the third wave," the study said.
The boosted group also had a greater proportion of healthcare workers and higher N95 use.
Of the 716 people who got infected even after taking a precautionary dose, three per cent were asymptomatic, 58.5 per cent had a mild infection, 37 per cent had moderate, and 0.3 per cent had severe disease.
The researchers also concluded that a long gap after the second dose correlated with a higher chance of infection during the third wave.
Also, "giving a third dose before a six-month gap did not make a difference in the infection rate", they said.
The study also showed that the third wave affected those aged below 40 the most -- around 45 per cent of them contracted the disease.
It said 39.6 per cent in the 40-59 age cohort and 31.8 per cent in the 60-79 age group reported Covid during the third wave. Only 21.2 per cent of the people aged above 80 were infected.
The third wave fuelled by the Omicron variant of the coronavirus and it infected more women (41 per cent) than men (36.8 per cent).
Among the 2,311 people who were infected during the third wave, 4.8 per cent were asymptomatic while 53 per cent had mild symptoms. Moderate severity was reported by 41.5 per cent, while 0.69 per cent had severe disease.
The researchers said Covaxin and Covishield recipients had the same rate of infection.
A total of 5,157 took Covishield and 2010 (39 per cent) of them reported Covid during the third wave. Of the 523 people who took Covaxin, 210 (40 per cent) reported getting infected.
The third wave of the pandemic hit India in late December last year and subsided by March.
The government authorised a third dose of the same vaccine for healthcare and frontline workers, and the people aged above 60 from January 10 to mitigate the severity of infections, hospitalisation, and death.
The administration of the precautionary dose to the 18-plus population through private vaccination centres started across the country on April 10.
