The new strain of the COVID-19 virus detected in South Africa is more worrying than the one found in the UK, according to British Health Secretary Matt Hancock.

In an interview with BBC, Hancock said the South African variant could be even more of a risk than the British strain, a reason flights from the country has been restricted.

Britain’s ITV Robert Peston also said some experts are not confident that the vaccines developed against. COVID-19 will work on the South African variant.

According to scientists, the new South African variant has multiple mutations in the important “spike” protein, and has also been associated with a higher viral load—possibly the reason for being more contagious.