WASHINGTON, United States (AFP)— People vaccinated against COVID-19 in high-risk parts of the United States should resume wearing masks indoors, the top health authority said Tuesday, a major reversal in guidance that underscored the country’s struggle to suppress the Delta variant.

President Joe Biden said the announcement showed that America needs to “do better” on vaccinations, adding that a vaccine mandate for the country’s more than two million federal workers was now “under consideration.”

Centers for Disease Control and Prevention director Rochelle Walensky cited new data that shows rare breakthrough cases involving Delta have an increased risk of onward transmission.

“In areas with substantial and high transmission, CDC recommends fully vaccinated people wear masks in public indoor settings,” she said.

As recently as last week, the CDC had defended its surprise decision in May that vaccinated people did not have to wear masks indoors in most circumstances.

In another setback, the White House on Tuesday also ordered all its staff to mask up again due to local transmission rates in Washington.

According to the latest CDC data, 63 per cent of the country’s more than 3,200 counties are experiencing substantial or high transmission.

Substantial is defined as being between 50 to 100 daily cases per 100,000 people over seven days, while high is defined as more than 100 daily cases per 100,000 over seven days.

Biden said he would lay out new steps on Thursday to overcome the lag in vaccinations after the country’s strong start to its program.

– Viral load –

In a separate address to the US intelligence community, when asked about a possible vaccine mandate for US federal workers, Biden replied: “That’s under consideration right now.”

On Monday, the Veterans Affairs department said it would require its frontline health workers, some 115,000 people, to get the shot, becoming the first federal agency to institute the requirement.

Walensky stressed that so-called “breakthrough” cases among people who are vaccinated remain rare — shots reduce the risk of symptomatic disease seven-fold, and hospitalizations and deaths by a factor of twenty.

However, new CDC research showed that when a vaccinated person does become infected, their viral load is similar to an unvaccinated person.

“That leads us to believe that the breakthrough infections, rare as they are, have the potential to forward transmit at the same capacity of an unvaccinated person,” she said.

To stem the spread of the Delta variant, the CDC will recommend schools adopt universal masking, including teachers, staff, students and visitors, regardless of vaccination status, when they reopen in fall, she added.

Infection numbers in the United States are now swelling, thanks to the Delta variant, which accounts for around 90 per cent of cases.

The latest seven-day average of daily cases is more than 56,000, similar to levels last seen in April.

In total, more than 610,000 people have died of COVID-19 in the United States.

Forty-nine per cent of the US population is fully vaccinated, but the vaccination rate is heavily skewed towards politically liberal parts of the country.

Walenksy stressed she saw masks as a “temporary” measure, adding: “What we really need to do to drive down these transmissions in areas of high transmission is to get more and more people vaccinated.