11% of vaccinated health staff in Delhi hospital got Covid-19, reveals study

A study of infections among health care workers, who are typically repeatedly exposed to Sars-cov-2, at a Delhi hospital found that 11% of those who had both doses of a coronavirus vaccine developed Covid-19.

The infections among the 36 out of roughly 297 health care staff of Maulana Azad Medical College who had received both doses of Covaxin or Covishield were mostly mild. Only two of these people required hospitalisation and oxygen support, and both recovered, suggesting 100% protection against death.

The rate of infection after vaccination – referred to as a breakthrough infection – in the hospital appeared to be higher than seen in other facilities: Chandigarh’s Postgraduate Institute of Medical Education and Research (PGIMER) reported 1.6% infections in fully vaccinated individuals while Delhi’s Indraprastha Apollo hospital reported 2.62% infections.

But this could depend on when these re-infections took place, experts said, pointing to the possibility the outbreak itself may have been less severe when the other two studies were done.

In the case of Maulana Azad Medical College, the cases were from the April-may wave of infections. In all, 326 health care workers from the hospital were covered, of whom 90.9% had received both the doses.

The study is yet to undergo peer review.

Among those partially vaccinated, there were 65 infections. “Evidence from a previous study suggests that a single dose induced higher concentration of neutralising IGG antibody in those having a history of natural infection and recovery from Covid-19,” the study said.

The researchers tried to look at factors such as age, gender, or any other variable that could predict breakthrough infections but none of the correlations were statistically significant.

The study found that in 20% of the cases, all family members of those who had the breakthrough infection concurrently had Covid-19, and in 44.6% cases, at least one other member of the family was also infected.

“We found a higher rate of breakthrough infections than reported from some other hospitals; the study does not focus on the reason. But it may be because during the April-may surge in cases, there were variants (of the infection) circulating in the city against which the vaccines might not be as effective,” said Dr Pragya Sharma, the lead author of the paper and a professor of community medicine at Maulana Azad Medical College.

The data from Pgi-chandigarh was taken when the vaccination drive began. “It could also be because the 2,000-bed hospital has been exclusively treating Covid-19 patients,” said Dr Sharma.

Dr Jacob John, former head of the department of virology at Christian Medical College-vellore, agreed. “The vaccine does not protect against an infection; it prevents severe disease and death. When we say that the efficacy of a vaccine is 80%, there will be 20% people who will get the infection. Hence, we cannot call it breakthrough infection as it is not the aim of the vaccine. The incidence of infection after vaccination is a function of the environment and not the efficacy of the vaccine. Higher the exposure, the more likely it is that there will be more cases.”

The second nationwide wave of infections — in Delhi, it was the fourth — was also believed to have been triggered by the Delta variant, or B.1.617.2. First found in India, this variant has since emerged as being somewhat more resistant to vaccines, particularly in those who have had just one dose.