The delta variant of coronavirus can avoid antibodies that target specific parts of the virus, according to a new study published Thursday in Nature. The results explain the reduced effectiveness of the vaccines against delta, compared with other variants.
The variant, first identified in India, is thought to be about 60% more contagious than alpha, the version of the virus that infected 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 such as Malaysia, Portugal, Indonesia and Australia.
Delta is now the dominant variant in the United States. Infections in the country had plagued at the lowest levels since early in the pandemic, although numbers may increase. Nevertheless, hospitalizations and deaths related to the virus still have a steep drop. This is partly due to relatively high vaccination rates: 48% of Americans are fully vaccinated and 55% have received at least one dose.
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However, the new study found that delta was barely sensitive to a dose of vaccine, and confirmed previous research that suggested that the variant may partially escape the immune system – although to a lesser extent than beta, the variant first identified in South Africa.
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.
The researchers looked at blood samples from 103 people who had been infected with coronavirus. Delta was much less sensitive than alpha to samples from unvaccinated people in this group, the study found.
One dose of vaccine significantly increased susceptibility, suggesting that individuals who have recovered from COVID-19 still need to be vaccinated to ward off some variants.
The team also analyzed samples from 59 people after receiving the first and second doses of AstraZeneca or Pfizer BioNTech vaccines.
Blood samples from only 10% of people vaccinated with a dose of AstraZeneca or the Pfizer-BioNTech vaccines were able to neutralize the delta and beta variants in laboratory experiments. But a new dose increased the number to 95%. There was no significant difference in the levels of antibodies elicited by the two vaccines.
“A single dose of Pfizer or AstraZeneca was either poorly or not at all effective against beta and delta variants,” the researchers concluded. Data from Israel and the United Kingdom largely support this finding, although these studies suggest that a single dose of vaccine is still sufficient to prevent hospitalization or death from the virus.
The delta variant also did not respond to bamlanivimab, the monoclonal antibody made by Eli Lilly, according to the new study. Fortunately, three other monoclonal antibodies tested in the study retained their efficacy against the variant.
In April, citing the increase in variants resistant to bamlanivimab, the Food and Drug Administration revoked the authorization for emergency use as a single treatment in the treatment of COVID-19 patients.
Separately, Pfizer announced on Thursday that it has developed a version of the vaccine that is targeted at the delta variant and expects to start clinical trials in August.
The company also reported promising results from studies of people who received a third dose of the original vaccine. A booster given six months after the second dose increases the potency of antibodies to the original virus and beta variant by five to ten times, the company said in a press release.
Antibody levels may drop six months after immunization, Pfizer said, and booster doses may be needed to ward off variations. However, antibodies are not the only part of the body’s immune response, and other studies have suggested that immunity induced by full vaccination is likely to remain robust for years, even against variants.
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