The experiment used medical records covering 5.4 million people, or 99% of the Scottish population and focused on people who had received a single shot of either the Pfizer-BioNTech vaccine or the AstraZeneca-Oxford vaccine, the only two shots authorized in the UK.
One dose helped protect against hospitalization, with effectiveness peaking about five weeks after immunization at 84% effective at preventing hospitalization.
But the follow-up data available beyond that time is where it gets concerning. Effectiveness peaked and then began to decline, going from 84% effective in the fifth week to 61% effective the following week and then 58% beyond then.
It’s unknown whether that trend would continue beyond that, as that’s all the data the researchers had available to crunch in the study. But the findings suggest that protection starts to wane from a single dose after five weeks or so.
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