More than four million Chinese netizens have signed a joint letter as of 3 pm Wednesday, demanding the World Health Organization (WHO) to send virologists, laboratory safety experts and biochemical specialists independent of geopolitics influence of the US to investigate the Fort Detrick lab.

The joint signing points to unanswered questions of wide concern. In July 2019, an unexplained respiratory disease appeared in northern Virginia, while a large-scale e-cigarette disease broke out in Wisconsin. These patients shared similar symptoms with those confirmed carrying COVID-19. Coincidentally, the Fort Detrick lab was suddenly shut down in the same month by the United States Centers for Disease Control and Prevention (CDC) for "national security reasons", with the department refusing to release more information since.

It's natural for people to link the e-cigarette disease with COVID-19 due to the lab’s closure and national attitude. Fort Detrick was dubbed "the center of the US government’s darkest experiments" by Politico Magazine. Lab specimens of anthrax spores, the Ebola virus and other deadly pathogens disappeared from the lab in the early 1990s. Though the US is trying to figure out the origin of COVID-19, why is it keeping silent on Fort Detrick? Is there something the US is trying to hide?

The US has been targeting China since the pandemic outbreak. It has not only questioned the conclusion drawn by WHO experts, but also ordered US intelligence to look into the origin of the virus, hyping the "lab-leak" theory. People can't help asking, is this a distractive move?

While Wuhan Institute of Virology has opened its doors to the WHO and foreign media in order to support COVID-19 origin tracing, Fort Detrick has avoided all probes. What is the US afraid of?

The US owes the international community an explanation.