Immunizations Run in the Family

The act of getting a flu shot could be contagious.

According to a study conducted by two Oregon researchers, children of flu-immunized parents are 2.77 times more likely to get vaccinated for that season. The team also discovered that, if after several years of not receiving a flu shot, parents decide to get immunized, their children are 5.44 times more likely to be immunized as well. “Encouraging parental immunization is a potential tool for increasing children’s immunization rates,” said Steve Robison, MPH, a researcher with the Oregon Public Health Division and lead author on the study.

Dr. Robison and his co-author pulled data from the Oregon ALERT Immunization Information System (ALERT IIS) on individuals residing in the Oregon Sentinel Surveillance Region, the six counties around the Portland metro area and the upper Willamette Valley. The Centers for Disease Control and Prevention (CDC) includes this area of Oregon in its immunization surveillance network program that tracks influenza and immunization trends across the country. This program has been in place since 2006 and is responsible for “special studies involving new vaccines and vaccine recommendations,” according to the CDC. The program also evaluates the cost-benefit of vaccine programs, and handles feasibility studies as well as new vaccine recommendations.

The Oregon study cohort included “matched adult caregiver-child pairs, based on children between 9 months and 17 years of age as of January 1, 2015, with a last-reported residence in the Oregon Sentinel Region.” Adult influenza vaccine history was compiled from data collected from the 2010-2011 flu season through the 2014-2015 flu season, while child vaccine history (including history of flu shots as well as other recommended vaccines) was collected from birth through June 30, 2015.

Oregon was chosen as the study site because more than 95% of Oregon children receive their vaccinations from clinics or medical practices that participate in the state’s Vaccines for Children program, which requires all administered immunizations to be reported. Similarly, Oregon pharmacies administer more than 40% of all adult flu vaccines, and must also report the administration of those immunization shots. “In the 2014-2015 influenza season, more than 1.3 million influenza immunizations were reported to the [program] out of an estimated total of 1.6 million given during the season,” the researchers observed.

The primary analysis in the study compared adult caregivers’ decisions to receive the flu shot themselves with their decisions to have their children immunized. The researchers noted that rates of child immunizations are likely overreported in Oregon, and, in contrast, adult immunizations may be underreported. In the secondary analysis, the group “compared adult influenza immunization in the 2014-2015 flu season with their children’s immunizations in a 4:3:1:3:3:1 series (4 diptheria-tetanus-acellular pertussis [DTaP], 3 polio, 1 measles-mumps-rubella, 3 hepatitis B, 3 Haemophilus influenza type b, 1 varicella) for those age 4 to 10, to 3+DTaP among those aged 9 months to 3 years, and to adolescent meningococcal and human papillomavirus immunizations for those age 11 to 17.”

The study included 450,687 children, 36.5% of whom received a flu shot during the 2014-2015 flu season. Similarly, 17.2% of those children’s corresponding adult caregivers also received a flu shot that season. As children aged, the rate of flu shot vaccination diminished. The researchers reported that children at the youngest age tier (ages 9 months to 3 years) were most likely to have received both influenza vaccinations and non-influenza vaccinations according to schedule, while children ages 4 to 6 years were 2.56 times more likely than their counterparts to get a flu shot if their parent was also immunized. Patients 7 to 10 years of age were 3.08 times more likely to receive flu shots if their caregivers got them, and children ages 11 to 17 years were 3.23 times more likely to get immunized if their caregivers also did. In general, “adults were also more likely to be immunized before or on the same day as their children,” Dr. Robison wrote.

The team determined that parental changes in flu shot “behavior” are mirrored by their children, meaning that “when parents change from immunizing to non-immunizing, their children are almost twice as likely to miss an influenza immunization,” the group reported. “When parents improve their own behavior, their children are more than 5 times more likely to also receive an influenza immunization,” they added.

If more parents and caregivers start receiving flu shots themselves, then it is likely that child immunization rates will increase, for influenza and other preventable diseases, the researchers believe.