Covid vaccines reduce transmission of the dominant Delta variant by about 40 percent, the WHO said Wednesday, warning that people were falling into a false sense of security.
The World Health Organization's chief Tedros Adhanom Ghebreyesus urged vaccinated people to continue to take measures to avoid catching Covid-19 and passing on the disease.
He noted that last week, more than 60 percent of all reported cases and deaths from Covid-19 were once again in Europe.
The sheer number of cases was translating into unsustainable pressure on health systems and exhausted health workers, he said.
"We're concerned about the false sense of security that vaccines have ended the pandemic and people who are vaccinated do not need to take any other precautions," Tedros told reporters.
"Vaccines save lives but they do not fully prevent transmission.
"Data suggests that before the arrival of the Delta variant, vaccines reduced transmission by about 60 percent. With Delta, that has dropped to about 40 percent."
The more transmissible Delta variant is now overwhelmingly dominant around the world, having all but crowded out other variants and the original strain.
Of 845,000 sequences uploaded to the GISAID global science initiative with specimens collected in the last 60 days, 99.8 percent were Delta, according to the WHO's weekly epidemiological report.
"If you are vaccinated, you have a much lower risk of severe disease and death but you are still at risk of being infected and infecting others," said Tedros.
"We cannot say this clearly enough: even if you are vaccinated, continue to take precautions to prevent becoming infected yourself, and infecting someone else who could die."