The Oxford findings are in line with an analysis by the US Centers for Disease Control and Prevention [File: Dado Ruvic/Reuters]

Washington, August 19 (RHC)-- The efficacy of two widely used coronavirus vaccines against the Delta variant weakens within three months of inoculation, but the jabs remain the most effective way to ensure protection against the strain, Oxford University researchers have found.

Two doses of the Pfizer and AstraZeneca vaccines provide protection levels of up to 75 and 61 percent respectively, 90 days after inoculation, they said in the largest study of its kind, published on Thursday.

That is down from 85 and 68 percent, respectively, seen two weeks after the second jab is administered.  The study was based on three million nose and throat swabs.

“Both of these vaccines, at two doses, are still doing really well against Delta … When you start very, very high, you got a long way to go,” said Sarah Walker, an Oxford University professor of medical statistics and the survey’s chief investigator.

Walker was not involved in work on AstraZeneca’s vaccine, which was initially developed by immunology experts at Oxford.  The researchers did not project how much more the protection would drop over time, but suggested that the efficacy of the two vaccines studied would converge within four to five months after the second shot.