The MedImmune Specialty Care division of AstraZeneca (MedImmune Specialty Care) has announced the publication of results from a new study that examined the burden of Respiratory Syncytial Virus (RSV) in preterm infants not receiving RSV immunoprophylaxis. The "RSV Respiratory Events Among Preterm Infants Outcomes and Risk Tracking" (REPORT) study is the first large, prospective study with active surveillance for laboratory-confirmed RSV disease in U.S. preterm infants born between 32 and 35 weeks gestational age (wGA). The study was published in the The Pediatric Infectious Disease Journal.

"I hope this study prompts a conversation about how best to identify infants at high risk of severe RSV disease."

The findings highlight the significant risk RSV poses to preterm infants. Infants 32-35 wGA were found to have substantial risk of RSV disease requiring medical attention through 6 months of age. The RSV-related hospitalization rate in the study (4.9%) was nearly three times greater than the rate reported in the general population of U.S. infants <6 months of age. Of those hospitalized for RSV, 16 percent required care in the intensive care unit (ICU) and 11 percent required mechanical ventilation.

The study highlighted that two environmental risk factors for RSV - attending daycare or having preschool-aged non-multiple birth siblings - are linked to a significant elevation in a preterm infant's risk of developing severe RSV disease. Hospitalization rates among preterm infants <6 months of age with these risk factors were significantly higher than all other preterm infants enrolled (9.2% per season versus 3.5% for all other infants, P<0.001); these infants also accounted for 75 percent of RSV ICU admissions observed in the study population.

These data support the risk factors recommended by the American Academy of Pediatrics for the identification of higher-risk 32-34 wGA infants for RSV prophylaxis. A significant burden of severe RSV disease was also observed in 35 wGA infants with these risk factors.

"The significant burden of RSV disease observed in this study highlights the risk of RSV hospitalization facing infants born between 32-35 weeks gestational age," said study co-investigator Dr. Eric Simões, MD, University of Colorado. "What's more insightful, however, are the findings that indicate a high risk for RSV-related hospitalization among certain sub-groups of infants within this population."

Currently, RSV prophylaxis recommendations issued by the American Academy of Pediatrics (AAP) exclude otherwise healthy infants 35 wGA. Infants 32-34 wGA are recommended to receive RSV prophylaxis if they have one of two AAP risk factors, and only until they are 90 days old. REPORT evaluated these wGA categories, environmental risk factors and chronological age when evaluating the burden of RSV disease.

Additional details of the findings from the study include:

Among those <6 months of age with AAP risk factors, RSV hospitalization rates were similar among 35 wGA infants and 32-34 wGA infants (9.3% per season vs. 8.9% per season). Infants with AAP risk factors continued to be at high risk for RSV hospitalization through 6 months of age, beyond the currently recommended 90-day cut-off for RSV prophylaxis Approximately 13 percent of all infants enrolled were eligible for RSV prophylaxis, but did not receive a single dose. These infants were more likely to be African American and Hispanic and of higher birthweight (>1500 grams).

"These results represent recent high-quality data regarding the burden of RSV in US preterm infants born at 32-35 weeks gestation," explained Dr. Simões. "I hope this study prompts a conversation about how best to identify infants at high risk of severe RSV disease."

RSV is the most common respiratory infection in infancy; approximately one-half of all infants are infected with RSV during the first year of life, and nearly all children have been infected at least once by the time they reach their second birthday. In most children, RSV disease presents with mild symptoms similar to the common cold and doesn't require medical attention. However, some infants - particularly preterm infants and babies with certain types of congenital heart disease (CHD) and chronic lung disease (CLD) of prematurity - are at increased risk of developing a serious infection from RSV, often requiring hospitalization.

The online version of this MedImmune-funded study is available here.

For more information on RSV and the REPORT study, please visit