US health officials have confirmed fewer than 6,000 cases of Covid-19 in fully vaccinated Americans, according to the Centers for Disease Control and Prevention (CDC) Director Dr. Rochelle Walensky. Seventy-four of them died.

The cases represent just 0.007% of the 84 million Americans who have been fully vaccinated, reports CNBC. Despite the 'breakthrough' infections, Dr Walensky this week said the vaccines are working as intended. 

Read Half of US adults have received at least one COVID-19 shot

"With any vaccine, we expect such rare cases, but so far out of more than 84 million people who were fully vaccinated, we have only received reports of less than 6,000 breakthrough cases," Walensky told reporters at a press briefing on Monday. Breakthrough cases are defined as someone contracting the virus more than 14 days after their second shot of the vaccine, i.e. when they can be said to be fully vaccinated.

"Although this number is from 43 states and territories and likely an underestimate, it still makes a really important point, these vaccines are working. Of the nearly 6,000 cases, approximately 30% had no symptoms at all," Walensky said. "This is really encouraging news. It demonstrates what we’ve already discussed about these vaccines. They also help prevent you from getting seriously ill."

Also read: Oregon: CDC investigating woman’s death after J&J vaccine

Out of the 6,000 or so breakthrough infections, 396 people were hospitalized and 74 people died, according to CDC data released last week.

The breakthrough infections have been reported in people of all ages. Around 45% of the infections were in patients over 60 years old. 

Some 65% of these breakthrough infections have been reported in females. 

Also read: Global Covid-19 cases cross 144 million

Half of all American adults have received at least one dose of the coronavirus vaccine. Of those aged 65 and older, 81% have received one dose or more and about two-thirds are fully vaccinated.

CDC's breakthrough case investigations

According to the CDC, there will be "a small percentage of people who are fully vaccinated who still get sick, are hospitalized, or die from COVID-19." Variants will cause some of these breakthroughs. 

Also read: Fully vaccinated people can travel safely again, CDC says

It adds that "[t]o date, no unexpected patterns have been identified in the case demographics or vaccine characteristics among people with reported vaccine breakthrough infections." The CDC website reiterates that the Covid-19 vaccines are effective, and recommends that all eligible people get a COVID-19 vaccine as soon as one is available to them.