A new CDC study found the flu vaccine was 38% effective last year, but it also stopped more than 100,000 hospitalizations.
Melissa Rolfes, PhD, MPH
The 2017-2018 flu season was a standout season—and not in a good way—with 79,000 flu-related deaths and the highest number of flu cases since the 2009 swine flu outbreak. And yet, a new analysis by the Centers for Disease Control and Prevention shows that matters could have been much worse had it not been for the influenza vaccine.
The flu vaccine prevented 7.1 million illnesses, according to the analysis, along with 109,000 hospitalizations, and 8000 deaths. Hospitalizations were 10% less than would be expected without the vaccine and 41% lower among young children ages 6 months to 4 years. This despite the fact that last year’s flu vaccine was found to only be 38% effective.
“We hope that our findings are helpful for clinicians to use when they talk to their patients about getting vaccinated against influenza and we hope that the findings can be a trigger for the general public to seek out vaccination, too,” said Melissa Rolfes, PhD, MPH, an epidemiologist in the CDC’s influenza division, and the lead author of the study.
The CDC estimates that about 42% of the US population received a flu vaccine in the 2017-2018 flu season.
“With our current vaccines, if more people were to be vaccinated, more people would be protected and the burden of influenza would be lower,” she said. “On the other hand, better vaccine effectiveness could generate greater protection. It’s important to find a balance between promoting the use of existing vaccines while at the same time pursuing enhanced vaccines that might offer better protection.”
Strategies to improve vaccine efficacy include increasing the antigen dose in vaccines, and looking for non-egg-based methods of vaccine cultivation. The latter would specifically be helpful with A(H3N2) viruses, Rolfes said.
“Most influenza vaccines are produced with viruses that are propagated in eggs; and the influenza A(H3N2) viruses that are passaged in eggs tend to adapt changes that move the virus further and further away from the original A(H3N2) that was placed in the egg,” she explained.
That can lead to vaccines that are more reactive against the egg-based version of the virus than against the real-world version. She said there are some commercially available vaccines that aren’t egg-based, but there isn’t enough data yet to know if they outperform their egg-based counterparts, or if any benefit would persist from year to year.
In the meantime, Rolfes said it isn’t too late for patients to get the flu vaccine—doing so could still have important public health benefits. Even if the vaccine effectiveness is just 38%, for thousands of people each year, taking the vaccine or not could be a life or death decision.
“It’s humbling, and honestly scary, to see that thousands of people get hospitalized and die from influenza each year—it is not a benign infection and even healthy people can succumb to flu,” she said.
The study, “Effects of Influenza Vaccination in the United States during the 2017—2018 Influenza Season,” was published in Clinical Infectious Diseases.