Cat flue

Hey ppl,can a pitbull or anyathr dog,get sick 4rm cat flue 4the 2cnd time?my pit spend the whole wk at the vet last wk bcz of cat flue,and yar i dd take it 2the vet wen he was 6wks 4the vecsin.5in1 and again the nxt mth aftr,and stil got sick,evin the doc ddnt undrstnd y he gt sick,and nw am just afraid that he wil gt sick again.we paid around 1600 4the bil,i 4gt 2ask the doc at the vet,and nw am askin u guys.