One jab has almost no effect against Delta: study

Two shots are better than one when it comes to protection against the SARS-CoV-2 Delta, as well as other, variants of the virus. Plus, vaccination of people previously infected with SARS-CCoV-2 is likely to be protective against a variety of circulating viral strains, including the Delta variant, according to a study recently published in Nature. However, people who have not been infected with SARS-CoV-2, and received only a single dose of either the Pfizer or the AstraZeneca vaccine produced “a barely detectable level of neutralizing antibodies against the Delta variant,” the study said. For the study, researchers in France examined how sensitive the Delta variant (SARS-CoV-2 B.1.617.2) was to antibodies resulting from vaccination, as well as from patients who had recovered from COVID-19. Findings relating to the Delta strain were compared to antibody responses to other strains of SARS-CoV-2. Read: Six things to tell patients about the Delta variant Sera samples used in the study were from two European cohorts which, combined, included a mix of people who had recovered from COVID-19, people never infected, and various vaccination statuses. The Delta variant sample used in the study was from a hospitalized patient with COVID-19 who had returned to France from India. After the comparisons were made, it was found that when it came to people who had not been infected with SARS-CoV-2, a single dose of either the Pfizer or the AstraZeneca vaccine gave poor protection against the Delta variant. In fact, only about 10% of the sera neutralized the variant. However, a two-dose regimen of vaccines “generated high sero-neutralization levels against the Alpha, Beta and Delta variants in individuals sampled at week 8 to week 16 after vaccination. Levels of neutralizing antibodies are highly predictive of immune protection from symptomatic SARS-CoV-2 infection,” the study said. It was also found that sera collected from people who had recovered from COVID-19 (up to 12 months after the onset of symptoms) were fourfold less potent against the Delta variant relative to the Alpha variant. Read: What do we know about the science behind breakthrough COVID cases? Two doses of the vaccine showed a neutralizing response in 95% of individuals, with titres three- to fivefold lower against the Delta variant than against the Alpha variant. “These results strongly suggest that vaccination of previously infected individuals is likely to be protective against a large array of circulating viral strains,” the authors wrote.

One jab has almost no effect against Delta: study

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