How do you stop a stomach bug from going through the whole family?

Norovirus-type bugs spread extremely efficiently, and hand sanitiser is notably poor against them — soap and water is what works. Practical measures that actually help: the ill person uses a separate towel and ideally a separate bathroom if possible, wash hands properly after any contact, clean high-touch surfaces with a bleach-based cleaner rather than a general spray, and wash soiled laundry separately on a hot cycle. The infectious period continues for about 48 hours after symptoms stop, which is why families get a second wave.