Delta variant: No antibodies in 16% after second dose of Covishield, says study

Neutralising antibodies against the Delta variant (B1.617.2) were not observed in 58.1% of serum samples from those given one shot of the Oxford/AstraZeneca vaccine produced in India as Covishield, according to a yet-to-be peer reviewed study by researchers from the Indian Council of Medical Research (ICMR).

After two doses, the neutralising antibodies could not be detected in 16.1% of the samples, the study found.

Additionally, the researchers saw that a prior infection along with vaccination produced much higher titres of neutralising antibodies.

“Not observed is not equivalent to not present. The levels of neutralising antibodies could be significantly low that it did not get detected, but it may still be there and protect the person against infection and severe disease.

Also, there would be some cell mediated protective immunity as well that can protect against infection and severe disease,” said Dr T Jacob John, former head of the department of microbiology at Christian Medical College-Vellore.

The titres of the neutralising antibodies – that specifically target the Sars-CoV-2 virus and kill it or prevent it from entering human cells – were also lower against the Delta variant as compared to the B1 variant that led to the first wave of infections in India.

As compared to B1, the neutralising antibody titres against the Delta variant were 78% less in those who received one shot, 69% in those who received two shots, 66% in those who had the infection and received one shot, and 38% in those who had the infection and received both shots.

What the study means for India’s vaccination drive is that some might require an additional booster shot of Covishield while those who have had the infection may require just one. “Assuming that the serum used for the study was from healthy individuals, the proportion of individuals with unobserved levels of neutralising antibodies will be higher among those who are old, comorbid, have chronic diseases as their immune response is lower. What this means is that men (women produce higher levels of antibodies) over the age of 65 years, those with diabetes, hypertension, chronic heart, lung, kidney diseases, or who are undergoing treatment for cancer should be given a third dose,” said Dr Jacob John.