@Bronwen3, there is a whole thread about the coronavirus here: https://community.withairbnb.com/t5/Hosting/ABB-s-policy-towards-endemic-disease-is-insane/td-p/1221...
@Joy298had the opposite problem, i.e. being unable to cancel guests from the Wuhan region. Wuhan and several other districts have been quarantined by the Chinese government; therefore, people cannot enter or leave. It sounds like your guests would have had no choice but to cancel their plans, meaning that they would have met the extenuating circumstances policy. According to Airbnb terms of service:
9.2 Guests can cancel a confirmed booking at any time pursuant to the Listing’s cancellation policy set by the Host, and Airbnb Payments will refund the amount of the Total Fees due to the Guest in accordance with such cancellation policy. Unless extenuating circumstances exist, any portion of the Total Fees due to the Host under the applicable cancellation policy will be remitted to the Host by Airbnb Payments pursuant to the Payments Terms.
As hosts, we have agreed to the terms of service. Frankly, I'd be happy that Airbnb did this. Going forward, yes, you could decline booking requests from guests from affected areas.