Effect of influenza virus vaccination in infants and children, with antibody studies

Summary 1. From October, 1946, to March, 1947, 100 children ranging in ages from one month to 18 years were inoculated with influenza virus type A and B vaccine adsorbed on calcium phosphate. The dosages given to the different age groups have been outlined. 2. Reactions were mild and consisted of slight local soreness for twenty-fourhours in the majority of cases. Four children had a slight febrile reaction (100° to 100.6° F.), and one child had an elevation of temperature to 102.° F. Nodules following injection appeared in eight cases and persisted for a short time only. 3. Of the 100 children inculated, complete serologic data including pre-andpostvaccination antibody titers were obtained in forty children. 4. Of these forty children, twenty-two received a second injection of thevaccine, at intervals from two weeks to three months. Complete serologic data was obtained in five children following the second inoculation. There were no systemic reactions to the second injection of the vaccine. In our study there were no cases of induced sensitivity to the calcium phosphate-adsorbed vaccine in those children who received more than one injection. 5. Two hundred children of similar ages as the vaccinated children servedas controls. In the injected children there were three cases of influenza, an attack rate of 3 per cent and in the controls there were nineteen cases, an attack rate of 9.5 per cent. 6. There was a significant response to vaccination in children over 2 yearsof age, as judged by antibody levels, for serologic evidence indicated that the injected children had a rise in titer from seven to twenty-three times. 7. Although the average antibody response to injection in children over 2years of age was, on the whole, very satisfactory, and comparable to adults, there was an unevenness of this response as some children did not produce antibody against the PR8 strain and others failed to produce a satisfactory increase in antibody against the Lee strain. 8. It is probably significant that children below 2 years of age did not respond to the vaccine with good antibody production. 9. It was observed that the second inoculation did not produce a further sharp rise in circulating antibody in children over 2 years of age. 10. The results of our studies are in agreement with the data and observations of other investigators; namely, that subcutaneous vaccination with a vaccine containing inactivated influenza virus, types A and B, adsorbed on calcium phosphate is usually followed by a satisfactory rise in circulating antibody against these viruses in children over 2 years of age. 11. In view of the fact that a widespread epidemic of influenza anticipatedduring the fall and winter of 1946–1947 did not fully materialize, the number of cases of influenza was far below expectancy. Although our vaccinated group had a reduction in the attack rate, further studies are needed to prove conclusively the clinical efficacy of influenza vaccination in children, and no final conclusion regarding the protective effect of influenza vaccination in children can be drawn from this study.