At 6-8 weeks of age puppies should receive their first vaccination; this is temporary and needs to be followed up with another one at 12 weeks. After the 12 week vaccination you can then take your puppy out in public areas.
You can be contagious from a few days up to two weeks or more, depending on which virus is causing your stomach flu (gastroenteritis).
A number of viruses can cause gastroenteritis, including noroviruses and rotaviruses. The contagious period â the time during which a sick person can give the illness to others â is slightly different for each virus. 1  Norovirus.2  With norovirus â the most common cause of viral gastroenteritis in adults and children â you're contagious from the moment you begin to feel ill. number of viruses can cause gastroenteritis, including noroviruses and rotaviruses. The contagious period â the time during which a sick person can give the illness to others â is slightly different for each virus. 1  Norovirus.