A World Health Organization (WHO) expert said on Monday that the past week has seen an 11% increase in COVID-19 cases worldwide, raising concerns that measures to halt the pandemic’s spread may be breaking down just as vaccine distribution picks up.

“In the past week we have seen an 11% increase in transmission across the world,” WHO epidemiologist Maria van Kerkhove, the technical lead on COVID-19, told a news conference. “It is not the time to let up.”