SAN DIEGO – Children who received the influenza vaccine at school were three times less likely to become infected with the influenza virus and missed half the of number of school days during the flu season, compared with their counterparts who did not, results from a large study showed.
The finding "supports the implementation of school-located influenza immunization programs to bring down the rates of flu in this age group," lead researcher Dr. Pia S. Pannaraj said during a press telephone conference in advance of IDWeek.
During the 2010-2011 influenza season, Dr. Pannaraj and her associates conducted active influenza surveillance among 4,455 children enrolled at eight elementary schools in the Los Angeles area with similar sociodemographic characteristics. Four of the schools served as controls while the other half served as intervention sites, where school-located influenza vaccination was offered. The researchers conducted polymerase chain reaction (PCR) testing for respiratory viruses on nose and throat swabs collected from febrile children with influenzalike illness to the school nurse or during absenteeism.
"A fundamental difference between this study and previous studies is that [our] research actively documented the reasons for absences and confirmed cases of flu instead of relying on parent surveys," noted Dr. Pannaraj of the department of pediatrics at the University of Southern California, Los Angeles.
Between 27% and 47% of students attending an intervention school received at least one dose of influenza vaccine. Dr. Pannaraj reported findings from 1,021 PCR specimens obtained from 898 children during the 15-week surveillance period. Of these 898 specimens, 21% were positive for influenza, including 2009 H1N1 (31%), H3 (9%), and B (60%). An additional 126 children (12%) tested positive for other respiratory viruses.
Rates of influenza were significantly higher among control schools, compared with schools where vaccination was offered (5.8 vs. 4.0 per 100 children, respectively; P = .011). Unvaccinated children who attended any school were 3.1 times more likely to acquire influenza infection, compared with vaccinated children (5.5 vs. 1.8 per 100 children, respectively; P less than .001).
Rates of absenteeism were higher among control schools compared with schools where vaccination was offered (4.2 vs. 3.9 days per 100 school days, respectively; P = .02), and children with influenza missed more school days, compared with those who had developed other respiratory viruses (a median of 2 days vs. 1 day, respectively; P less than .001).
Protection for unvaccinated children was observed in one school that achieved a vaccination rate of 47% (odds ratio, 2.1; P = .039). In an interview, she speculated that efforts to achieve a 50% vaccination rate in elementary schools "might be a target number to use in planning for pandemics, or even in preparing for the regular flu season. More studies are needed to be sure," she said in advance of the combined annual meetings of the Infectious Diseases Society of America, the Society for Healthcare Epidemiology of America, the HIV Medicine Association, and the Pediatric Infectious Diseases Society.
Dr. Pannaraj said that she had no relevant financial conflicts to disclose. One of the study investigators, Dr. Laurene Mascola, disclosed being a member of the speakers bureau and receiving speaker honorarium from Merck and MedImmune.