The delta variant of the coronavirus can evade antibodies that target specific parts of the virus, according to a new study published in Nature on Thursday. The results provide an explanation for the reduced effectiveness of the vaccines against Delta compared to other variants.
The variant first identified in India is believed to be about 60 percent more contagious than Alpha, the version of the virus that hit Britain and much of Europe earlier this year, and perhaps twice as contagious as the original coronavirus. The delta variant is now causing outbreaks among unvaccinated populations in countries like Malaysia, Portugal, Indonesia and Australia.
Delta is now also the dominant variant in the USA. Infections in the country have been at their lowest level since the pandemic began, although the numbers may rise. Still, hospital admissions and deaths related to the virus have continued a steep slump. This is partly due to the relatively high vaccination rates: 48 percent of Americans are fully vaccinated, 55 percent have received at least one dose.
But the new study found that Delta was barely sensitive to a dose of the vaccine, confirming previous research suggesting the variant can partially bypass the immune system – albeit to a lesser extent than Beta, the variant first identified in South Africa.
French researchers tested how well antibodies produced by natural infections and by coronavirus vaccines neutralize the alpha, beta and delta variants, as well as a reference variant that is similar to the original version of the virus.
The researchers examined blood samples from 103 people infected with the coronavirus. Delta was much less sensitive than Alpha to samples from unvaccinated individuals in this group, the study found.
One dose of vaccine increased sensitivity significantly, suggesting that people who have recovered from Covid-19 may still need to be vaccinated to fight off some variants.
The team also analyzed samples from 59 people after receiving the first and second doses of the AstraZeneca or Pfizer-BioNTech vaccines.
Blood samples from just 10 percent of those immunized with a dose of the AstraZeneca or Pfizer-BioNTech vaccines were able to neutralize the Delta and Beta variants in laboratory tests. But a second dose increased that number to 95 percent. There was not much difference in the levels of antibodies produced by the two vaccines.
“A single dose of Pfizer or AstraZeneca was either poorly effective or not effective at all against beta and delta variants,” the researchers concluded. Data from Israel and the UK broadly support this finding, although these studies suggest that one dose of vaccine is still enough to prevent hospitalization or death from the virus.
According to the new study, the Delta variant also did not react to Bamlanivimab, the monoclonal antibody from Eli Lilly. Fortunately, three other monoclonal antibodies tested in the study retained their effectiveness against the variant.
In April, the US Food and Drug Administration revoked the emergency approval for the treatment of Covid-19 patients as a single treatment, citing the increase in variants resistant to bamlanivimab.