A single dose of the Oxford vaccine may reduce transmission of coronavirus by two-thirds, according to a new study.
Researchers said that the first dose of the Oxford/AstraZeneca jab offers protection of 76% up to three months and may reduce transmission by 67%, with efficacy rising to 82.4% after the second dose 12 weeks later.
It comes amid worries about mutation in strains of the virus in the UK, with more than 100 cases of the South African variant having been identified in England so far.
Public Health England is investigating after tests showed they had a mutation that has been shown to reduce the effectiveness of vaccines.
No cases of the South African variant have been found here to date, but Dr Ultan Power said it is only a matter of time.
The professor of molecular biology at Queen's University said the concern with the new variant is that it reduces the efficacy of the vaccine in that the antibodies induced after it is administered are not as effective.
"This is why we would be worried about this being introduced in Northern Ireland," he said on Radio Ulster's Nolan Show.
Suggestions from Chief Medical Officer Dr Michael McBride that the South African variant will eventually make its way here are "probably right". "We have free movement of people between Northern Ireland and England at this time," he added.
But people who have been vaccinated will be protected once they get the second dose, although the level of protection will be "slightly" diminished. "It will prevent severe disease still even with the South African and Kent strains," he said.
The flu vaccine tackles new strains every year and pharmaceutical companies producing the vaccines are already working to adapt to new strains of coronavirus, he added.
The answer is to get case numbers down to as low a level as possible during the vaccine rollout, the expert said.
"The more we give the virus the opportunity to circulate at high numbers in the community, the more we give the opportunity to the virus to mutate," he said.
The study from the University of Oxford, which has not yet been peer-reviewed, provides a major boost to recommendations from regulators, including the UK's, that the second jab should be delayed for up to 12 weeks.
Before these results little was known about how effective the Covid-19 vaccines were at preventing transmission of the disease.