Technically this canine vaccine is different, but they are kind of the same...
Both are vaccine acronyms for the viruses they protect against the following.
H -or- A2: Hepatitis /Adenovirus Type 2
In a DHPP vaccine, canine hepatitis protection is gained by Adenovirus type 1 (the canine hepatitis virus) in the vaccination, and is listed as "H".
In a DA2PP vaccination, canine hepatitis protection is gained by Adenovirus type 2, which cross protects against the hepatitis causing Adenovirus type 1, and is listed as "A2".