RESEARCHERS in Britain reported Wednesday they had found more evidence that two doses of Pfizer’s and AstraZeneca’s coronavirus vaccines protect people well against the Delta variant of coronavirus.
But a single dose of either vaccine provides very little protection against Delta, also known as B.1.617.2, the researchers reported in the New England Journal of Medicine.
The team looked at overall vaccine efficacy in England first when the Alpha variant, known also as B.1.1.7, was the predominate variant, and then when Delta took over.
The vaccines being given in England are Pfizer’s two-dose vaccine and AstraZeneca’s two dose vaccine.
“Effectiveness after one dose of vaccine was notably lower among persons with the Delta variant than among those with the Alpha variant; the results were similar for both vaccines,” Dr. Jamie Lopez Bernal of Public Health England and colleagues wrote.
Against Delta, a single dose of either vaccine was only about 30% effective, they found.
“With the BNT162b2 (Pfizer/BioNTech) vaccine, the effectiveness of two doses was 93.7% among persons with the Alpha variant and 88.0% among those with the Delta variant. With the ChAdOx1 (AstraZeneca) nCoV-19 vaccine, the effectiveness of two doses was 74.5% among persons with the Alpha variant and 67.0% among those with the Delta variant,” they added.
“Only modest differences in vaccine effectiveness were noted with the Delta variant as compared with the Alpha variant after the receipt of two vaccine doses,” it continued.
England’s complete database of medical records helped the team do the research.
“The large scale of testing and whole-genome sequencing in the United Kingdom, as well as the recording of vaccination status in a national vaccination register, allowed us to analyze vaccine effectiveness within a few weeks of the Delta variant first emerging in the United Kingdom,” they wrote.