February 10, 2000
Nasal Spray May Protect Young Children Against Unexpected Flu Strain
Bethesda, MD (SafetyAlerts) - An experimental nasal
spray flu vaccine protected young children against an influenza strain not expected to be
covered by the vaccine, according to results from the second year of a study supported by
the National Institute of Allergy and Infectious Diseases (NIAID) and the vaccine
In an unexpected twist, during the 1997-98 flu
season when the study took place, the predominant circulating flu virus was A/Sydney.
Since this strain had not emerged as an upcoming threat when the vaccine was made, the
vaccine was not designed to protect against it. Yet the nasal spray vaccine proved 86
percent effective against A/Sydney. In addition, none of the children became infected with
the three strains of influenza the vaccine was specifically designed to prevent.
An estimated 35 to 50 million Americans come down
with influenza each flu season, which typically lasts from November to March. Children are
two to three times more likely than adults to become ill with flu, and children frequently
spread the virus to others. Although most people recover from the illness, influenza's
deadly potential among vulnerable p opulations is often underestimated, and at least
20,000 people in the United States die from influenza and its complications each year.
"This study gave us an unanticipated
opportunity to test how well this vaccine works against a variant virus, an influenza
strain that had undergone so-called 'antigenic drift,'" says Linda Lambert, Ph.D.,
influenza program officer at NIAID. "Virus proteins important to disease
development," she explains, "had undergone minor, spontaneous changes. Still,
the vaccine performed remarkably well in this 'natural experiment.'"
Of the 71 cases of influenza seen in the study
children, 66 were caused by A/Sydney. Only 15 of the A/Sydney cases occurred among the 917
children who got FluMist(tm). These 15 children had significantly milder disease symptoms
-- shorter duration of fever, fewer cases of influenza-related middle-ear infections, and
no lower respiratory tract disease -- than did the 51 placebo recipients who developed
A/Sydney flu. All five cases of non-A/Sydney flu occurred among the 441 children in the
NIAID has supported the development of this
"cold-adapted" live virus influenza vaccine concept for nearly 25 years. Early
work by researchers in NIAID's Laboratory of Infectious Diseases and their colleagues at
the University of Michigan paved the way. They developed weakened influenza viruses that
could stimulate immunity in the cooler nasal passages but could not cause disease in the
warmer temperatures of the lower airways. Simpler versions of FluMist(tm) were tested by
NIAID-supported researchers in smaller trials. Then in 1995, Aviron entered into a
Cooperative Research and Development Agreement with NIAID for development of an advanced
version of the vaccine into a commercial product.