Other studies have investigated the persistence of bactericidal antibodies in young children after primary immunization and the level of immunogenicity after a preschool booster. The levels of bactericidal antibodies after primary 4CMenB vaccination at the ages of two, four, six, and 12 months had waned when measured at 40–44months, but an anamnestic response was observed following a booster dose given at the age of 40–44 months. Similarly, bactericidal antibody levels in infants who originally received 4CMenB during late infancy (6, 8, and 12 months) had also waned when measured at the age of 40 months but, once again, there was an anamnestic response to a booster dose given at 40 months.