Britain’s health chief said on Wednesday that a new study suggesting that a single dose of the Oxford-AstraZeneca COVID-19 vaccine provides a high level of protection for 12 weeks supports the government’s strategy of delaying the second shot so more people can quickly be protected by the first dose.

Britain’s decision has been criticised as risky by other European nations. Health Secretary Matt Hancock’s comments came after Oxford University released a study showing the vaccine cut the transmission of the virus by two-thirds and prevented severe disease.