Following a series of potentially fatal accidents in recent weeks involving anthrax and avian flu viruses, the Centers for Disease Control and Prevention (CDC) announced the temporary closure of the two labs involved.

The agency reported in June that dozens of its scientists may have been exposed to live anthrax bacteria after potentially infectious bacteria were sent out from one its secure labs, the BBC reported Friday. The bacteria, which were supposed to have been inactivated, were sent to labs that lacked the adequate equipments needed to handle live bacteria.  

In an earlier incident that was only disclosed Friday, it came to light that a CDC lab had accidentally contaminated a benign flu sample with a highly virulent strain of the H5N1 bird flu virus and sent it to a government lab.  

In a report on the mishandling of the anthrax samples, published Friday, the agency said that the “overriding factor” that contributed to the incident was “the lack of an approved study plan reviewed by senior staff or scientific leadership to ensure that the research design was appropriate and met all laboratory safety requirements.”

“This is not the first time an event of this nature has occurred at CDC,” the report added.

CDC officials said that no one potentially exposed to anthrax had shown any signs of illness and that there had been no reported infections from the previous lapses.  

The agency also announced an immediate moratorium on all shipments of biological samples from high-security labs.

Stating that such events “should never have happened,” CDC Director Tom Frieden said he was “astonished” that such lapses had taken place. “I am disappointed, and frankly I am angry about it,” he told reporters in an hour-long press conference on Friday.

Frieden also expressed his frustration over the delay in reporting the bird flu incident, which reportedly happened in March and was confirmed in May. “It happened six weeks ago and I learned about it 48 hours ago,” he said.

 “Fundamentally, what the lapses revealed was totally unacceptable behavior. We need to look at our culture of safety throughout all of our laboratories,” Frieden said.

The revelations come just days after the recovery of smallpox samples in a cardboard box at a National Institutes of Health laboratory near Washington, D.C. By international agreement, only two labs in the world are supposed to store smallpox samples – the CDC in Atlanta and the State Research Centre of Virology and Biotechnology in Russia.

Frieden announced on Friday, that the samples, at least two of which contained the live virus, will be destroyed, adding that it should have been done “a couple of decades ago.”