A new study published in Influenza and Other Respiratory Viruses shows that influenza vaccination does not reduce absenteeism, or the number of days of school that kids miss because of flu, casting some doubt about how often the vaccine prevents severe illness in children ages 5 to 17 years.
The study contradicts previous research that showed lower absenteeism in vaccinated school-age children. Those studies looked at children suffering from any acute respiratory illnesses (ARIs). This is the first study to look at absentee rates among children with lab-confirmed flu, not just nonspecific respiratory illnesses, the authors said.
Results across three flu seasons
From 2012 through 2015 children who came to the Marshfield Clinic Research Foundation (in Marshfield, Wisconsin) for ARIs were tested for flu. If they were positive for influenza, they were surveyed 1 week later about vaccination status and number of school days missed.
Among 1,027 children, 2,295 days of school were missed because of medically attended ARIs. Influenza accounted for 40% of illnesses and 47% of days missed. Influenza caused more missed days of school (mean 0.96-1.19 days) than any other ARI.
The mean number of absences was not affected by flu subtype or strain, but children who presented with more symptoms, had higher fevers, and received a prescription for antivirals were more likely to miss school. But flu vaccination status had no effect on how many days, or if children missed school. Between 30% and 40% of the children testing positive for flu at the clinic had received a flu vaccine, said Huong McLean, PhD, MPH, lead author of the study and a researcher at the Marshfield Clinic.
"Our study confirms that flu is a major contributor to absenteeism, and vaccination status did not reduce this," said McLean. Also, surprisingly, results did not change when the 2014-15 flu season (a mismatched year for the vaccine) was excluded.
A question of severity
The major flaw of the study, according to McLean, was that it did not include the vaccine status of children who had influenza but mild enough symptoms to avoid a clinic visit. It's unknown, McLean said, if these children had milder illnesses because they received the flu vaccine.
"If someone gets sick and is coming into clinic, they are probably already sick enough to be missing school," said McLean. "So their vaccine status doesn't seem to matter."
Further studies, Mclean said, will need to determine if and how vaccination plays a role in milder forms of influenza.
The authors concluded, "Additional studies are needed among children who develop influenza despite vaccination to determine if influenza vaccine can reduce disease severity and duration, and subsequently school absenteeism."
Nov 25 Influenza Other Respir Viruses study