ANN ARBOR--Fully vaccinating children reduces the risk of hospitalization associated with influenza by 54%, according to a study by researchers at the University of Michigan, the Clalit Research Institute, and Ben-Gurion University in Israel.

The study, published in the December 2019 issue of the journal Clinical Infectious Disease, is one of the few studies worldwide that has tested the effectiveness of childhood vaccination against influenza and risk of hospitalization due to influenza complications.

In Israel, as in the United States, government guidelines recommend that children 8 or younger who have never been vaccinated, or who have only gotten one dose of flu vaccine previously, should receive two doses of vaccine.

Children vaccinated according to government guidelines are much better protected from influenza than those who only receive one vaccine, said Hannah Segaloff, a research fellow at the U-M School of Public Health and lead author of the study.

"Over half of our study population had underlying conditions that may put them at high risk for severe influenza-related complications, so preventing influenza in this group is critically important," she said. "Our results also showed that the vaccine was effective in three different seasons with different circulating viruses, reinforcing the importance of getting an influenza vaccine every year no matter what virus is circulating."

The retrospective study used data from Clalit Health Services, the largest health fund in Israel, to review the vaccination data of 3,746 hospitalizations of children 6 months to 8 years old at six hospitals in Israel. They were tested for influenza over three winter seasons 2015-16, 2016-17 and 2017-18.

Not only do the findings reveal that the flu vaccine reduced hospitalizations associated with the flu by 54%, but they show that giving two vaccine doses to children up to age 8 who have never been vaccinated or only received one dose previously is more effective than administering one dose, in accordance with the Israel Ministry of Health's recommendations.

"Young children are at high risk of hospitalization due to influenza complications," said study co-author Mark Katz, a senior researcher at the Clalit Research Institute, the research arm of Clalit Health Services, and an adjunct associate clinical professor at the BGU School of Public Health and Medical School for International Health.

"Children with underlying illnesses such as asthma and heart disease have an even greater risk of getting the complications. It is important to prevent influenza infections in these populations."

The findings support health organizations' recommendations, including the Israel Ministry of Health to vaccinate children against influenza every year, preferably before the onset of winter or early childhood. Children under 5 are defined as having a high risk of influenza complications.

"This study mirrors a previous study we conducted at Clalit Institute where we found that flu vaccine reduces 40% risk of hospitalizations in pregnant women," said Ran Balicer, director of the Clalit Research Institute and professor at the BGU School of Public Health.

"It reaffirms that vaccination is the most effective way to prevent both the flu and hospitalization. We hope parents will be aware of these facts and make an informed decision about the importance of vaccinating their children."

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The researchers hope that this study and additional research will increase vaccination rates among the general public and, especially, children.