However, none of the nearly 600 vaccine recipients required hospitalization.
In an indicator of the diminishing role of vaccines in preventing the transmission of the coronavirus, a little over 25% of the fully vaccinated health care workers of a Delhi hospital contract a fresh or ‘breakthrough’ infection. However, none of the nearly 600 vaccine recipients reportedly required hospitalization. While there have been previous reports of similar infections in other studies in India, this is the first time that such a high percentage has been reported as part of a study.
The study involved health care workers in Max Group hospitals in Delhi and Gurugram and was led by scientists from CSIR-Institute of Genomics and Integrative Biology (CSIR-IGIB). This appears as a preprint and has not been reviewed yet.
The time between the first and second doses varied, but 482 received a second dose within 42 days of the first dose. About half of the recipients were previously infected with SARS-CoV-2.
To confirm a re-infection, the researchers relied on antibody levels that were directed toward the nucleocapsid region of the coronavirus, which is different from the region (spike protein) that vaccine-generated antibodies normally target. Currently, all vaccines are designed to produce antibodies against the spike-protein and therefore high levels of antibodies against the nucleocapsid region were taken as a marker of a new coronavirus infection. A successful infection is one where a person tests positive at least two weeks after their second dose.
Shantanu Sengupta of CSIR-IGIB and one of the scientists who led the study said that 25% was a “conservative estimate” because many infections were likely asymptomatic and only a subset of them were likely to manifest symptoms on their own. Get tested.
While the infections were mild, this may have contributed to healthcare workers unknowingly infecting patients, Dr Sengupta said. For their analysis, the scientists relied on blood samples taken every week – up to 90 – after vaccination and because this period coincided with the second wave in India, where most infections were due to the delta variant, it was the most There was a possibility that these were breakthrough infections as well. Because of the delta version. “Two doses of the vaccine were not protective against infection, but post-vaccination infection — even a single dose — was quite protective against fresh infection,” he said.
Even at present, the delta and its associated lineages comprise about half of the coronavirus infections and are believed to be promoting infections in Kerala and Maharashtra.
Health care workers who were previously infected had a re-infection rate of 2.5% over the same period.
Consistent with emerging evidence from several countries, such as the United States and Israel, where successive infections are being reported despite half the population being vaccinated, the study underscores that India may not be immune to the phenomenon. .
“The neutralization of the delta variant by antibodies against the non-delta spike protein is greatly reduced. This means that neither prior infection by non-delta forms, nor existing vaccines, are individually sufficient for the route of herd immunity. This also implies that masking is an essential part of any rational COVID control strategy, which is agnostic to avoidance of immunity,” the authors note in their study.
The authors say the data indicate “the urgency to explore routes towards more effective use of vaccines”. Because a single dose of ChAdOx1-nCoV19 to previously infected subjects induces humoral immunity comparable or better than two doses in nave subjects, a single dose may be optimally directed to a population with high seropositivity.