Almost 2 million additional cases of influenza could have been averted last season if 70% of Americans got the vaccine — a national target for overall coverage.
Even small increases in vaccine effectiveness and coverage could have had a large impact on patient health, according to newly presented findings.
The CDC recommends all Americans aged 6 months and older get vaccinated against influenza each season, but coverage rates consistently fall well below target levels and vaccine effectiveness is often between 40% to 60%.
To assess the impact of modest increases in vaccine effectiveness and coverage, Michelle M. Hughes, PhD, Epidemic Intelligence Service (EIS) officer in the CDC’s Influenza Division, and colleagues used a mathematical model based on federal surveillance data from the 2016-2017 influenza season. According to recently published CDC estimates for the 2016-2017 season, the vaccine was close to 40% effective, and coverage was around 47%, preventing an estimated 5.29 million illnesses and 84,700 hospitalizations.
The model showed that a 5% to 10% increase in vaccine effectiveness could have prevented an additional 698,000 to 1.38 million illnesses and 16,600 to 32,900 hospitalizations, while a 5% to 10% increase in vaccination coverage could have had a similar effect, preventing 483,000 to 960,000 more illnesses and 6,950 to 13,800 more hospitalizations, Hughes and colleagues reported.
If coverage reached the Healthy People 2020 target of 70% vaccine coverage, 1.88 million additional illnesses and 17,300 hospitalizations could have been averted, they said.
Hughes presented the findings on Monday during the EIS conference in Atlanta, where disease detectives from the federal agency meet annually to present research conducted over the previous year. She said the same modeling could be used for 2017-2018 once data for the season is finalized and may produce even higher estimates.
The U.S. has experienced very high levels of influenza-related illness and hospitalizations this season — a burden driven by low vaccine effectiveness and a predominant strain, H3N2, that is difficult to target with the vaccine.
“The model depends on a season’s burden of disease, vaccination coverage and vaccination effectiveness,” Hughes told Infectious Disease News. “The projections may be higher for the 2017-2018 season due to a higher burden of disease. However, the projections also depend on vaccination and coverage.”
The 2017-2018 influenza season overwhelmed some hospitals, caused spot shortages of antivirals and rapid influenza tests and exacerbated a national shortage of IV saline linked to Hurricane Maria’s impact in Puerto Rico. Hughes and colleagues did not estimate the impact that increased vaccination would have on health care infrastructure, but there would likely be one.
“Reducing the numbers of influenza-related hospitalizations and outpatient visits could reduce the use of IV bags, testing kits and antivirals in future epidemics, but the impact on possible shortages is unclear and would require additional research,” Hughes said. “What we do know is that the increased use of the influenza vaccine and/or the use of a more effective influenza vaccine would prevent a substantial number of additional influenza-associated illnesses, outpatient visits, and hospitalizations.” – by Gerard Gallagher
CDC. Estimated influenza illnesses, medical visits, and hospitalizations averted by vaccination in the United States. https://www.cdc.gov/flu/about/disease/2016-17.htm. Accessed April 16, 2018.
Hughes MM, et al. Modeling projected impact of increased vaccination effectiveness and coverage on influenza burden — United States, 2016-2017. Presented at: Epidemic Intelligence Service conference; April 16-19, 2018; Atlanta.
Disclosures: The authors report no relevant financial disclosures.