The health authorities in the United States announced Tuesday that vaccinated Americans should wear a mask in high-risk indoor places, amid an increase in highly-contagious Delta cases and a slowed-down vaccine campaign. 

"In areas where transmission of (Covid-19) infection is significant, health authorities recommend fully vaccinated individuals to wear masks in indoor public places," said Rochelle Walensky, director of the Centers for Disease Prevention and Control.

Walinsky said that the effectiveness of vaccines against the Delta mutant is great, but new data "indicates that in rare cases, some of the vaccinated may be carriers of infection and cause transmission of the virus to others."

She described this new data as "alarming and necessitates updating our recommendations."

According to the latest data from the Centers for Disease Control and Prevention, most of the southern regions of the United States have a steady or large outbreak. 

Walinsky said that the Centers for Disease Prevention and Control will recommend making masks compulsory in schools for teachers, staff, students and visitors, regardless of the vaccination status of people.

Recently, the Centers for Disease Prevention and Control defended a recommendation it issued in May, which said that those vaccinated are not obligated to wear masks in closed places in most cases, with specific exceptions that include shared transportation and hospitals.

However, the number of cases is currently increasing due to the Delta mutant, which now accounts for about 90 percent of injuries.

The last weekly average of daily cases in the US exceeds 56,000, which is similar to what was recorded in April.

49 percent of the population of the United States has become fully vaccinated, but the vaccination campaign is witnessing a large disparity according to the political orientations of the regions, especially between those that are liberal and conservative.

The vaccination is "a solution to a problem caused by the large unvaccinated population," Eric Sayo-Pina, director of public health at Northwell Network, told AFP.