Hello, Sorry about this illness in grandson. Most probably your husband will have lifelong immunity from an attack of this virus.
Please however ask him to contact virologist or infectious disease specialist in China if he develops any rash.
Medicine will be available in such case there.
Took too long to reply considering the scant reply when it came and had to contact own GP who provided a much more detailed answer for free.
Good system in UK. Good luck to him in his business trip.