Report: Irrespective of vaccination, you can be a silent COVID carrier

Vaccinated healthcare workers could be silent carriers, cautions a study conducted among Delhi’s healthcare workers. The study conducted by a team of researchers, which is published as a pre-print article in MedRixiv – an online archive for health science – indicates that the asymptomatic infection of the Delta variant could be high among fully vaccinated healthcare workers.

Transmission from health workers to patients, especially those who are under critical care, is a worrying aspect, experts said.

The rate of breakthrough infection among healthcare workers in Delhi is found to be 25.3 per cent – most cases were asymptomatic. The study indicates that the Delta variant causes frequent asymptomatic breakthrough infections among immunised people, reducing the herd effect of immunity.

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This categorically reinforces the need of a pragmatic strategy of masking, sanitising and social distancing for a longer period of time. The Delta variant could cause frequent breakthrough infections and minimal impeding transmission.

Among Delhi’s 597 healthcare workers, 309 (52 per cent) were fully vaccinated and were previously infected with SARS-CoV-2. The possibility of breakthrough infection is far higher for those who were un-infected before vaccination compared to those who were infected.

The breakthrough infection rate was found to be 25.3 per cent among the fully vaccinated and uninfected health workers. On the contrary, the breakthrough infection prevalence was only 2.5 per cent for those who had been infected before vaccination. However, the severity leading to hospitalization was found to be zero for all health workers who were the subject of the study.

Another important finding is that neutralization of Delta variant by antibodies to non-Delta spike protein is greatly reduced.

“This means that neither prior infection by non-Delta nor existing vaccines are individually sufficient for the path to herd immunity.What we have to learn from this study is that masking is very essential,” says Shantanu Sen Gupta, Senior Scientist at CSIR-Institute of Genomics and Integrative Biology, one of the corresponding authors of the article.

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He told The Federal that the data of breakthrough infection might not reflect the actual situation because the asymptomatic re-infections might not be counted. Generally people go for testing only if they are symptomatic.

“The actual number of breakthrough infections could be higher considering the occurrence of asymptomatic reinfections”. The study suggests that the true rate of infection is likely to be much higher since vaccination is known to reduce symptoms and increase test-seeking threshold.

The study suggests a single dose of vaccine should not be expected to confer any protection against Delta variant infection, and second dose should be given early, preferably within six weeks, as it was done for HCW.

“We found that 48.4 per cent of previously uninfected subjects had a vaccination breakthrough after single dose within the period of this study. That is unacceptably high,” states the article.

On the other hand, it is also found that a single dose seemed sufficient for previously infected individuals (by Delta variant) in terms of absolute antibody levels as well as neutralisation activity.

The data shows that vaccination breakthroughs were far more common during the Delta-outbreak in Delhi than previously reported. Natural infection was seen to provide a strongly boosted response to vaccination, according to the study.