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The delta variant of the coronavirus can escape antibodies that target parts of the virus, according to a new study published Thursday in Nature. The results provide an explanation for the reduced efficacy of delta vaccines, compared to other variants.
The variant, first identified in India, is believed to be around 60% more contagious than the alpha, the version of the virus that hit Britain and much of Europe earlier this year, and possibly twice as contagious as the original coronavirus. The delta variant is now causing epidemics among unvaccinated populations in countries like Malaysia, Portugal, Indonesia and Australia.
Delta is now the dominant variant in the United States. Infections in the country had peaked at their lowest levels since the start of the pandemic, although the numbers may rise. Yet hospitalizations and deaths linked to the virus continued to drop. This is in part because of the relatively high vaccination rates: 48% of Americans are fully vaccinated and 55% have received at least one dose.
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But the new study found that delta was barely sensitive to a dose of the vaccine, confirming previous research that suggested the variant may partially elude the immune system – albeit to a lesser degree than beta, the variant identified for the first time in South Africa.
French researchers tested the extent to which antibodies produced by natural infection and by coronavirus vaccines neutralize alpha, beta and delta variants, as well as a reference variant similar to the original version of the virus.
Researchers examined blood samples from 103 people infected with the coronavirus. Delta was much less sensitive than alpha to samples from unvaccinated people in this group, according to the study.
One dose of vaccine significantly increased sensitivity, suggesting that people who have recovered from COVID-19 still need to be vaccinated to fend off certain 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 immunized with a dose of AstraZeneca or Pfizer-BioNTech vaccines were able to neutralize the delta and beta variants in laboratory experiments. But a second dose increased that number to 95%. There was no major difference in the antibody levels induced by the two vaccines.
“A single dose of Pfizer or AstraZeneca was either little or not at all effective against the beta and delta variants,” the researchers concluded. Data from Israel and Britain largely support this conclusion, although these studies suggest that one dose of the 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 effectiveness against the variant.
In April, citing the increase in bamlanivimab-resistant variants, the Food and Drug Administration revoked authorization for emergency use for its use as a sole treatment in treating COVID-19 patients.
Separately, Pfizer announced Thursday that it is developing a version of its vaccine that targets the delta variant and plans to launch clinical trials in August.
The company also reported promising results from studies in people who received a third dose of the original vaccine. A booster given six months after the second dose increases the potency of antibodies against the original virus and the beta variant by five to ten times, the company said in a press release.
Antibody levels may decline six months after vaccination, Pfizer said, and booster doses may be needed to fend off variants. But antibodies aren’t 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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