Study Shows Flu Vaccine Reduces Risk of Severe Illness

August 1, 2018 — A new CDC-supported study published in Vaccine conducted over multiple flu seasons shows that getting a flu shot lessened the risk of severe influenza (flu) among adults, including reducing the risk of hospitalization and admission to the intensive care unit (ICU), and also lessened the severity of illness. CDC recommends an annual flu vaccine for everyone 6 months and older. Annual flu vaccination varies in how well it works, but it is the best available way to prevent flu and its potentially serious consequences.

The study was conducted over four flu seasons from 2012 to 2015 and found that flu vaccination prevented severe disease:

  • Flu vaccination among adults reduced the risk of being admitted to the hospital with flu and placed in a general ward bed by 37 percent.
  • Flu vaccination was even more effective in preventing the most severe forms of flu and reduced the risk of being admitted to an ICU with flu by 82 percent.

Risk among vaccinated vs. unvaccinated

Because flu vaccine varies in how well it works and people who are vaccinated may still get sick, the study also looked at whether flu vaccination reduced the severity of illness among hospitalized people who were vaccinated compared to those who were unvaccinated and found that:

  • Among adults who were admitted to the hospital with flu, vaccinated adults were 59 percent less likely to have very severe illness resulting in ICU admission than those who had not been vaccinated.
  • Among adults in the ICU with flu, vaccinated patients on average spent 4 fewer days in the hospital than those who were not vaccinated previously.

The study was a collaborative project with CDC, conducted through the Southern Hemisphere Influenza and Vaccine Effectiveness Research and Surveillance project, which prospectively enrolled hospitalized adults 18 years and older from 2012 to 2015 in Auckland, New Zealand. Eligible hospitalized patients were those who had an overnight admission with acute respiratory illness. Once enrolled in the study, patients self-reported their flu vaccination status and were tested for flu infection by RT-PCR.

Since 2005, CDC has conducted annual flu vaccine effectiveness studies to assess how well the vaccine works in preventing medically attended illness. Until recently, there were few studies that looked at how well the vaccine works in preventing serious outcomes like admission to ICU. This study adds to a growing body of evidence that supports the importance of vaccination in order to prevent more serious flu outcomes.

About Vaccine

Vaccine is the pre-eminent journal for those interested in vaccines and vaccination. It is the official journal of The Edward Jenner Society and The Japanese Society for Vaccinology and is published by Elsevier

Copies of this paper are available to credentialed journalists upon request; please contact Elsevier’s Newsroom at or +31 20 485 2719.

Study title: “Influenza Vaccine Effectiveness in Preventing Influenza-Associated Intensive Care Admissions and Attenuating Severe Disease among Adults in New Zealand 2012-2015”, by Mark G. Thompson, PhD, Nevil Pierse, PhD, Q. Sue Huang, PhD, Namrata Prasad, MPH, Jazmin Duque, MPH, E. Claire Newbern, PhD, Michael G. Baker, MD, Nikki Turner, MD and Colin McArthur MD. DOI: ( ). It appears in Vaccine, (In press, Corrected proof) published by Elsevier.