There’s some misunderstanding in the posts above about the circumstances. Just hours before the CBS announcement the World Health Organization raised its level of concern on the potential for this particular virus the spread from High to Very High, its most severe level of concern. In addition, a second case was identified in the U.S. that was unrelated to travelers from an area of infection or from the quarantined cruise ship in Japan. It’s highly concerning because it demonstrates community transmission of the virus in places where protocols are not in place to reduce transmission. And then the coronavirus was now confirmed to have cases on every continent, except Antartica. This includes Africa, (including sub-Saharan Africa) Australia and South America. The coronavirus while not transmitted through the air, can last in an open environment for nine days. Symptoms are nor consistent, some people have mild symptoms and can die, others will have severe symptoms and survive. And you can be exposed to ad become ill more than once. So there’s no established natural immunity.
And it is still not clear what the incubation period is. Travel has become a major concern for transmission as well as inadequate means of isolating people who may have been exposed or have been exposed or have come down with the illness.
It’s clear that production had run out of options for filming additional legs due to these circumstances. With the now global spread of the coronavirus it can’t. Be considered seasonal like the flu, and it is not a flu to begin with. SARS was the closest thing they’ve seen like this, but the newer coronavirus appears to have features to make it harder to treat and control. Official a vaccine or treatment is thought to be 12 to 18 months away, but some potential treatments are already undergoing human trials to expedite this.
The other immediate issue to shortages of the tests need to detect coronavirus, and other supplies such as masks on a global basis. Many medical masks are not the right type for coronavirus, and would be ineffective.
Personally the filming could resume wherever production chooses for the fourth leg, they wouldn’t have to return to a particular location from the three filmed legs. I suspect affected third parties (I.e., employers and so forth can be persuaded to cooperate under the circumstances.
Just remember, there hasn’t been anything like this in a century, the 1919 pandemic. And this is the first season to be drastically affect since TAR 2, filmed immediately after 9/11 when security constraints were unexpectedly difficult. And that was worked out.