Thank you for writing.
It's recommended that the pneumococcal vaccination be repeated every five years. It would not hurt to have the repeat vaccine at four years but there is no benefit to getting it before 5 years. Is there a way you can narrow down when he/she had the first vaccination? If not then you need to work with his/her physician who can take his/her medical history (and look up records) into consideration to determine whether to start the process all over or give him/her the standard second dose of the vaccination.