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Covishield protected 97.4% of staff from infection in a Delhi hospital, IJMR study finds

Study period was from 16 January to 24 April 2021, among 3,235 healthcare workers of Delhi's Indraprastha Apollo Hospital. Only 85 reported symptomatic infection after vaccination.

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New Delhi: During the devastating second wave, Covishield vaccine provided 97.4 per cent protection from Covid infection among over 3,000 healthcare workers at a hospital in Delhi, with none of the breakthrough infections leading to deaths, a study has found.

In the study published in the Indian Journal of Medical Research Monday, a team from Indraprastha Apollo Hospitals looked at the number of symptomatic Covid infections reported among 3,235 healthcare workers who had received either one or both shots of Serum Institute of India’s Covishield vaccine.

The study period was during the initial phase of the vaccination drive, from 16 January to 24 April (100 days).

Of the 3,235 healthcare workers, only 85 reported symptomatic infection after vaccination. This represents a breakthrough infection rate of 2.63 per cent.

The study also noted that the infection rate among women healthcare workers was 1.84 times higher than men. This, the researchers said, could be because women had greater involvement in patient care, working as nursing personnel.

According to the study, the likelihood of a breakthrough infection was the highest among nursing staff (41.18 per cent) followed by the medical staff (32.94 per cent).

Most of those who tested Covid-positive after both doses got the infection between six to 64 days after vaccination. Among those who got Covid after one dose, the time period ranged from two to 53 days after vaccination.

The researchers also pointed out that most of the breakthrough infections occurred in the later part of the study in April 2021, during the second wave of Covid-19.

In all the 85 infected cases, there were mild symptoms such as cough, fever, malaise and loss of taste and smell. Only two — that is 0.06% of the vaccinated healthcare workers — required hospital admission, with none requiring an ICU admission.

No Covid deaths were reported among those vaccinated.

Vaccine benefit increases with time

The study further added that the estimated benefit of vaccination increases in magnitude with the passage of time.

The infection after vaccination was as low as 2.65 per cent after the first dose, and 2.63 per cent after the second dose among those observed for less than 100 days.

“This implied that a reasonable level of immunity was achieved after a single shot of vaccine which might get further enhanced with the second dose, in a longer follow-up,” the researchers wrote.

The authors, however, acknowledged that healthcare workers were not tested for Covid if they did not have symptoms. This may have led to ‘over reporting’ the protective effect of the vaccine. They also noted that the study size was relatively small.

(Edited by Neha Mahajan)

Also read: Why 25-50% of vaccine side-effects are ‘anxiety-related and not a result of Covid jab’


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