Measles Vaccination V. The Booster Effect of Purified Hemagglutinin in Children Previously Immunized with this Product or Formalin-Killed Vaccine

Two groups of children immunized at the age of 6 months to two years with three monthly doses of either formalin-killed (FK) or Tween-ether (TE) measles vaccine were submitted to clinical and serological follow-up analysis up till 17 months after vaccination and then given a booster of TE vaccine of moderate potency. Among 8 cases of clearcut exposure to measles before the booster 6 responded with mild clinical symtoms; 3 without and 3 with a faint rash. An increase in HI serum titer was recorded in 3 out of the 6 cases. All of them had received FK vaccine. Between 11 and 17 months after vaccination no change in HI titers was demonstrable. After the booster the geometric mean HI titer increased 20 times in children primarily vaccinated with TE vaccine and 83 times in children given FK vaccine. In the pre-booster serum samples only 75 antibodies were detectable, where-as the post-booster serum samples in addition to 75 antibodies contained 1 to 3% 19S antibodies.