Complex sentence: The first vaccine against canine distemper was developed in 1923 and 1924 by an Italian named Puntoni, although he did not use a large population of dogs for his trials, his work shows dogs can be vaccinated against this disease producing solid immunity.
Split into simpler sentences: The first vaccine against canine distemper was developed in 1923 and 1924 by an Italian named Puntoni. Although he did not use a large population of dogs for his trials, his work shows that dogs can be vaccinated against this disease, producing solid immunity.