The protection provided by two doses of the Pfizer/BioNTech and the AstraZeneca coronavirus vaccines starts to wane within six months, new research suggests.
A reasonable worst-case scenario could see protection fall to below 50% for the elderly and healthcare workers by winter, an expert has said.
RTE News is reporting that the Pfizer jab was 88% effective at preventing Covid-19 infection a month after the second dose.
But after five to six months the protection decreased to 74%, suggesting protection fell 14 percentage points in four months, latest analysis from the Zoe Covid study indicates.
With the AstraZeneca vaccine, there was a protection against infection of 77% one month after the second dose.
After four to five months protection decreased to 67%, suggesting protection fell by 10 percentage points over three months.
The study drew on more than 1.2 million test results and participants.
The mid-term efficacy trial by Pfizer observed an initial 96.2% risk reduction in infection (up to two months after the second dose).
There was an 83.7% reduction more than four months after the second dose, a 12.5 percentage point risk reduction.
Real world analysis would be expected to show less protection than clinical trials, and the vaccines were not trialled against the now dominant Delta variant of the virus.
Read the full report here.