This work introduces and discusses the use of state sequence analysis (SSA) as an analytic framework for vaccination data. SSA is a well-known data-mining tool used in sociological literature however, to date, epidemiological studies featuring longitudinal categorical data have mostly relied on probabilistic models or summary measures at the aggregate level. Leveraging data on the uptake of hexavalent vaccine in the Lombardy region, we show how SSA helps in disentangling timeliness of vaccination.