EPIDEMIOLOGY AND CLINICAL IMPACT OF PARAINFLUENZA VIRUS-INFECTIONS INOTHERWISE HEALTHY INFANTS AND YOUNG-CHILDREN LESS-THAN-5 YEARS OLD

Over a 20-year period in a population of otherwise healthy children, r espiratory viruses have been cultured from nasal wash specimens from e ach child with a clinically significant respiratory illness. Since eff orts are underway to develop vaccines for prevention of illness due to parainfluenza virus (PIV) type 3, the epidemiologic characteristics o f PIVs were reviewed, and the population size necessary to demonstrate vaccine efficacy was estimated. A population of 1429 children was fol lowed through early childhood. PIVs were isolated from 286 samples, 17 .4% of positive viral cultures. PIV-3 was the most common: 10% of the children had at least one symptomatic, culture-proven PIV-3 infection. PIV-3 was endemic during the study period, while the other two PIVs, PIV-1 and -2, caused biennial flu epidemics. Only four PIV-related hos pitalizations were seen. The efficacy of a PIV-3 vaccine could be demo nstrated in a trial of 600 carefully monitored children vaccinated by 3 months and followed to 15 months of age.