Real-world studies show Pfizer and AstraZeneca still offer strong protection against severe disease.
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As rising coronavirus infections force some countries to reimpose restrictions, scientists and drugmakers are racing to answer a crucial question: how well do the current vaccines protect against the Delta variant? On one point, most observers agree. The leading shots, studies show, still offer strong protection against severe disease and hospitalization. “Real-world effectiveness studies with a number of vaccines show good protection especially against severe disease,” Soumya Swaminathan, chief scientist at the World Health Organization, told the Financial Times. “The most important priority just now is to scale up vaccination coverage in all countries.” So-called “real-world” analysis of 14,019 cases of the Delta variant in the UK, released by Public Health England in June, found the BioNTech/Pfizer and Oxford/AstraZeneca vaccines were, respectively, 96 percent and 92 percent effective against hospitalization after two doses.
Late on Thursday, Pfizer reiterated it believed its shot worked against Delta, especially after a potential third booster dose. But it also added it planned to study a variant-targeted inoculation, with trials slated to start as early as next month.
The high efficacy of the shots in the UK, where the Delta variant is dominant and more than half the population has been fully vaccinated, is reflected in the current mortality rate for Covid-19 patients, which at 0.085 percent is 20 times lower than at its peak, according to Meaghan Kall, an epidemiologist at PHE. But the question of whether the vaccines remain as effective at preventing infection, and therefore transmission and spread, is more fraught. Early figures from the real-world studies in the UK in May found that two doses of the Pfizer vaccine were 88 percent effective at preventing symptomatic infection with the Delta variant. A month later, that number was revised down to 79 percent by Scottish researchers.
Several Chinese scientists have said that some Chinese vaccines have been found to be less effective against Delta than against previous variants but few details of those studies have been released. Sinovac spokesman Liu Peicheng told Reuters that preliminary results based on blood samples from those vaccinated with its shot showed a three-fold reduction in neutralizing effect against Delta. Peter English, a public health expert who previously advised PHE, cautioned that while the data on efficacy against hospitalization was generally positive, the vaccines’ ability to prevent the transmission of Delta was far less clear. “Delta is so much more infectious, it’s better at finding people who aren’t sufficiently immune and infecting them,” he said, adding that it would take time for reliable numbers on transmission to accumulate.