Pfizer and BioNTech have begun a study to determine whether a third dose of their Covid-19 vaccine can offer protection against variant strains of the virus.
The US and German pharmaceutical giants released a statement Thursday to say they believed a third dose would boost the immune response against variants such as those first discovered in South Africa and the UK.
They are now testing the theory on a group of 144 people who received their first two doses between 6 and 12 months ago.
"We are taking multiple steps to act decisively and be ready in case a strain becomes resistant to the protection afforded by the vaccine," Pfizer CEO Albert Bourla said in a statement.
He later told US news channel NBC a third dose could potentially raise the antibody response by as many as 20 times.
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The manufacturers also maintain that the vaccine in its intended two-shot form also offers protection against the more drug-resistant variants.
Given 21 days apart, the two-shot vaccine has proven to be about 95 percent effective in protecting against the original Covid-19 strain.