World Health Organization officials held a news briefing Monday to discuss mutations in the coronavirus responsible for new strains in both South Africa and the U.K.

WHO Director-General Tedros Adhanom Ghebreyesus said the new strain of the virus spreading in the U.K. is reported to be more infectious, but there’s no evidence it is more deadly. He said that containing transmission of the coronavirus is key — the more opportunity the virus has to spread, the more opportunity it has to mutate.

The new strain of the virus in the U.K. prompted dozens of countries in the European Union and around the world to close their borders to travelers from the country, and for U.K. officials to tighten stay-at-home restrictions.

Epidemiologist Maria Van Kerkhove, the WHO’s technical lead for coronavirus, [Source: CBS News]