There is always a danger of vaccine reaction even with only a single vaccine.
Most traditionally vets continue to use the same vaccine protocol that they have beentaught in vet school. However, there is a growing trend toward in the holistic vet community, of giving less vaccines and performing vaccine titers instead.
Vaccine titers are measurements of vaccine antibodies in the blood, and tell the vet if the vaccine from the previous year is still adequate to prevent the disease. Many vaccines can protect much longer than the yearly limit of protection dictated by the vaccine manufacturers. Additionally, many vets split vaccines in smaller dogs, like the Shih-Tzu by giving no more than two vaccines per visit. It requires that you take your dog to the vet more often, and that can be an inconvenience.
In the future request the following for your dog: Titers in place of the Distemper combo vaccine; that only one vaccine be given per time to determine which vaccine is the cause of the vaccine reaction in your dog, and premedication with benedryl.