World Health Organization (WHO) officials have urged even fully vaccinated people to continue wearing masks and to keep taking other measures to prevent infection.
However the Centers for Disease Control and Prevention (CDC), on the other hand, told fully vaccinated Americans in May that they no longer needed to wear masks indoors or to maintain a distance of 6 feet from other people. The agency also eased advice about testing and quarantine after suspected exposure to the virus.
Asked on Monday about the new cautions expressed by WHO, a CDC spokesperson pointed to the existing guidance and gave no indication it would change.
A highly infectious form of the virus, called the Delta variant, was first detected in India and has been identified in at least 85 countries. In the United States, where its prevalence has doubled in the last two weeks, the variant is responsible for 1 in every 5 Covid-19 cases.
Dr Anthony Fauci, the nation's top infectious disease doctor, has called it the greatest threat to eliminating the virus in the United States.
The rise of new variants makes it even more urgent that we use all the tools at our disposal to prevent transmission, including consistent use of both vaccination and public health and social measures, Dr Tedros Adhanom Ghebreyesus, director-general of the WHO, said at a news briefing.
Dr Mariângela Simão, the WHO's assistant director-general for access to medicines, vaccines and pharmaceuticals, emphasized at the briefing that even vaccinated people should continue to consistently wear masks, avoid crowds and maintain social distance from others, make sure they are in well-ventilated spaces, wash their hands frequently, and avoid sneezing or coughing around other people.
What we're saying is, 'Once you've been fully vaccinated, continue to play it safe, because you could end up as part of a transmission chain.' You may not actually be fully protected, said Dr Bruce Aylward, a senior adviser to the WHO.
He added: I think the first message we want to be careful about is saying, 'Once you're vaccinated, you can just go ahead and do whatever'.
The comments were made in the context of broader statements criticising the inequitable distribution of vaccines around the globe and the lack of access to vaccination in many parts of the world where the virus is spreading.