U.K. Prime Minister Boris Johnson pushed back his plan to lift coronavirus restrictions by four weeks as a more infectious variant spreads rapidly across the U.K. and threatens to undermine the country’s effort to vaccinate its way out of the pandemic.

The government in London was forced to act after modeling showed hospital admissions could reach similar levels to the first wave of infections in spring 2020 — a peak of more than 3,000 a day — if Johnson stuck to his schedule to end social-distancing rules on June 21. In a televised briefing on Monday, he said there was no choice but to delay his plan until July 19.

The aim is to prevent a surge in hospitalizations and avoid adding thousands to what’s already Europe’s highest death toll by allowing more people to get their second vaccine dose. Johnson said he is "pretty confident” there won’t be another postponement, while some members of his governing Conservative Party hit out at the impact on the economy.