Hexyon has been studied in several countries worldwide in 12 main studies involving over 3,400 children between six weeks and two years of age who were given three doses of the vaccine during their first six months of life according to different local vaccination schedules. The effects were compared with a combination of separate vaccines designed to protect against the diseases included in Hexyon. The main measure of effectiveness was the production of antibody levels known to be protective against those diseases.

Five of these studies examined the effect of giving a booster dose at least 6 months after the initial vaccination schedule in 1,511 children. The studies showed that protective antibody levels against the various diseases developed in between 90 and 100% of children after the first three doses of Hexyon; protection was maintained or improved when a booster dose was given.

A subsequent study involving 455 children looked at the longer-term persistence of protective antibodies up to 3 years after a booster dose with Hexyon, and another study in 1336 children evaluated the response to different lots of the vaccine and what happened when it was given with vaccines for infections caused by the bacterium Streptococcus pneumoniae (Prevenar) and rotavirus (Rotarix). These studies showed that Hexyon produces similar antibody profiles over time to comparable vaccines, and that the vaccine can be given at the same time as Prevenar and Rotarix.

The two-dose vaccination schedule was investigated in an additional main study involving 554 children. In the study, children who either received Hexyon produced a similar antibody response to those who received a comparator vaccine (Infanrix hexa), when given as a two-dose schedule followed by a booster 6 months later.