North Korea’s successful launch of an intercontinental ballistic missile on July 4 heightened global fears about the deadly threat of nuclear war.

But nuclear weapons are not the only weapons of mass destruction that experts think North Korea is developing. They warn that the secretive state also possesses chemical weapon stores and may maintain an ongoing biological weapons program as well.

Biological weapons are particularly scary, since they could ignite a global disease pandemic as devastating as nuclear war — a threat Bill Gates wrote about in an op-ed for Business Insider in February.

The status and capabilities of North Korea’s biological weapons program are mysterious, Sonia Ben Ouagrham-Gormley, an associate professor at George Mason University and the author of “Barriers to Bioweapons”, wrote in a recent analysis for the Bulletin of the Atomic Scientists.

It’s likely that North Korea has been developing such weapons since the 1960s, according to most experts. Defectors and South Korean reports have suggested that North Korean researchers have worked with biological agents the US governments considers serious threats, including plague, anthrax, viral hemorrhagic fevers, and potentially smallpox.

An attack that uses such agents could be particularly scary since it can be difficult to ascertain where they came from.

“With biological weapons, especially, there’s an opportunity for covert attack with deniability, since attribution would be difficult,” Andrew C. Weber, former assistant secretary of defense for nuclear, chemical and biological weapons defense programs, recently told the Washington Post while discussing North Korea’s bioweapon capabilities.

An active bioweapons program?

It’s impossible to know how far along North Korea is in developing bioweapons, Ouagrham-Gormleywrote.

Kim Jong Un visited Pyongyang’s Bio-technical Institute in 2015, where he was photographed by North Korean television posing with lab equipment and military personnel. This effort was likely “designed to send a message to the United States: that North Korea has an active bioweapons program,” Ouagrham-Gormley wrote.

South Korean news reports have also indicated that North Korea is “likely capable” or “suspected” of being able to produce biological weapons.

But Ouagrham-Gormley suggested that if you look at the scientific requirements for maintaining such a program and the political and technological infrastructure required, “the odds that North Korea has established a successful bioweapons program appear much lower than some estimates would suggest.”

Still, other experts caution that the risk of these weapons is real and that such programs could be well-concealed.

A recent report written by North Korea expert Joseph S. Bermudez Jr. for the US Korea Institute and Johns Hopkins School of Advanced International Studies suggested that “North Korea has deliberately built its NBC [nuclear, biological, chemical] infrastructures in extreme secrecy; undertaken camouflage, concealment and deception operations to mask the NBC infrastructure; made extensive use of legitimate defensive or civilian industrial and research infrastructures; and dispersed NBC facilities around the country.”

That report identifies a number of different institutions as potentially linked to a biowarfare program.

Bruce Bennet of the global policy think tank the RAND Corporation echoed a similar sentiment when he testified about North Korea before Congress in 2013.

“Biological weapon programs are easier to hide than most military programs because they can be developed in a university setting or hidden within efforts to develop related vaccines,” he said. “As a result, the outside world has little direct information on North Korean biological weapons and therefore has mainly indirect inferences, creating substantial uncertainties.”

In 2015, a North Korean scientist defected to Finland with what he said was electronic documentation that showed North Korea had tested biological and chemical weapons on citizens. He’s not the only defector to make such allegations, though none of those claims have been confirmed.

The most recent event to spur speculation about North Korea’s bioweapons capabilities was the assassination of Kim Jong Nam, the half-brother of Kim Jong Un, which used the chemical weapon VX. Though VX is chemical, not biological, experts suggested that the event proved North Korea is willing to use these types of weapons. Continue reading.