Impact of a Fourth Hexavalent Vaccine Dose During Primary Vaccination After Haematopoietic Stem Cell Transplantation

It is recommended for patients who underwent an hematopoietic stem cell transplantation to receive, 6 months after the graft, 3 injections of hexavalent vaccine (diphteria-tetanus- poliomyelitis-pertussis-Hib-HBV) within 2 months, followed by a booster dose one yrar after. However, this strategy do not constantly lead to efficient antibody levels.

the investigators aim to determine whether a 4th dose in the initial vaccine schedule (month 0, 1, 2, and 3) allows to obtain a better response.

After informed consent, the investigators will recruit 6 months after the graft 200 patients who had received an hematopoietic stem cell transplantation . The participants will have a measure of their antibody level against 5 pathogens (diphteria toxin, tetanus toxin, Haemophilus influenza b, hepatitis B virus, poliomyelitis virus) at month 0 (before the 1st hexavalent vaccine injection), and one month after the 3rd injection of this vaccine. If the antibody response is not sufficient, they will be randomized for a 4th dose in the following month.

The one year booster dose will be then injected to all participants, and the antibody response will be again measured one month after this dose. The primary endpoint is to compare the antibody levels at this date in patients who had an unsufficient immune response after the 3rd dose and who received or not a 4rth dose in the initial vaccine schedule.