A new study, published in Nature, has concluded that this variant of the coronavirus was barely sensitive to one dose of vaccine and can evade antibodies that target certain parts of the virus.
Recent findings by ICMR also indicated lower levels of neutralizing antibodies against the Delta in a small portion of Covishield recipients.
The variant, first identified in India, is believed to be about 60% more contagious than alpha, the variant that had spread widely in Britain. It is now responsible for majority of new infections in US, Malaysia, Portugal, Indonesia and Australia.
For the new study, French researchers tested how well antibodies produced by natural infection and by coronavirus vaccines neutralize the alpha, beta and delta variants, as well as a reference variant similar to the original version of the virus.
They looked at blood samples from 103 people who had been infected with the coronavirus. Delta was much less sensitive than alpha to samples from unvaccinated people in this group, the study found.
One dose of vaccine significantly boosted the sensitivity, suggesting that people who have recovered from Covid-19 still need to be vaccinated to fend off some variants.
The team also analysed samples from 59 people after they had received the first and second doses of the AstraZeneca or Pfizer-BioNTech vaccines. Blood samples from 10% of people immunised with one dose were able to neutralise Delta and Beta in lab tests. But a second dose boosted that number to 95%. There was no major difference in the levels of antibodies elicited by the two vaccines. “A single dose of Pfizer or AZ was either poorly or not at all efficient against Beta and Delta,” the study said.
A separate study by the Indian Council of Medical Research also came to broadly similar conclusions.
The ICMR study indicated a 4.5-fold and 3.2-fold reduction in neutralising antibody levels against the Delta variant in those who were given one and two doses of Covishield, respectively, compared to an earlier SARS-CoV-2 version that had the D614G mutation (detected early last year).
For the study, serum samples were collected from healthy individuals who had received one or two doses of Covishield. Samples were also collected from Covid-recovered patients who had received one or two doses, as well as from people who had contracted Covid after vaccination.
It was found that two doses of vaccination resulted in greater resistance against the virus, for both healthy as well as recovered people.
(With agency inputs)