This Season’s Flu Vaccines Reduced Flu Medical Visits and Hospitalizations Across All Ages

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February 29, 2024 — Interim flu vaccine effectiveness estimates show that so far during the 2023-2024 flu season, flu vaccines have worked, substantially reducing the risk of flu-related medical visits and hospitalizations across all age groups, with some estimates higher than have been previously observed, even during well-matched seasons. Additionally, the data show that flu vaccination is working against both the influenza A and B viruses that have spread most commonly so far this season. CDC continues to recommend getting a yearly flu vaccine as long as flu viruses are spreading in the community.

Specifically, flu vaccination has reduced the risk of flu medical visits by about two-thirds and flu-related hospitalization by about half for vaccinated children and flu medical visits by half and hospitalization by about 40% for vaccinated adults. This is the first time that interim flu vaccine effectiveness estimates for children and adults from four major networks are available at the same time, providing extensive data on how well flu vaccines are working this season across influenza virus types, by age, and across a spectrum of illness severity.

Flu Vaccines Worked Across All Age Groups

Analyses were conducted in four different vaccine effectiveness networks, which provided consistent ranges of estimates across all age groups:

Children

Children (6 months-17 years) who got a flu vaccine were between 59%-67% less likely to visit a health care provider because of flu, and 52%-61% less likely to be hospitalized with flu.

Specifically:

For influenza A viruses overall, children who were vaccinated were 46%-59% less likely to visit a health care provider because of flu, and 46%-56% less likely to be hospitalized with flu.
- Vaccine effectiveness against influenza A(H1N1)pdm09 viruses was 54%-61% against flu-related health care provider visits and was 60% against flu-related hospitalizations.
- Flu vaccine effectiveness estimates were similar for influenza A(H3N2) viruses. Children who got a flu vaccine were 55% less likely to visit a health care provider for influenza A(H3N2).
For influenza B/Victoria lineage viruses, children who got a flu vaccine were 64%-89% less likely to visit a health care provider because of flu caused by that lineage of B viruses. (This is higher than has been typically observed during previous seasons.)

This is good news as many children are at higher risk of potentially serious flu complications either because they have a chronic medical condition or based on their age alone. Unfortunately, flu vaccine uptake among children so far this season is lagging compared to the same time last season and also compared to seasons before the COVID-19 pandemic. Additionally, disparities in flu vaccination coverage are worsening by urbanicity and race and ethnicity. Flu vaccination coverage in children living in rural areas is much lower compared with children living in urban and suburban areas. Additionally, flu vaccination coverage for Black children is lower compared with children of all other racial and ethnic groups in the United States. So far this season, 91 pediatric flu deaths have been reported to CDC. Similar to previous seasons, about 80% of these pediatric deaths occurred in children who were not fully vaccinated against flu.

Adults Overall

Consistent with the vaccine effectiveness estimates in children, flu vaccines have protected adults from flu-related health care provider visits and hospitalizations. For adults overall, those who got a flu vaccine were 33%–49% less likely to visit a doctor because of flu and 41%–44% less likely to be hospitalized with flu.

Specifically:

Against influenza A viruses overall, adults who got a flu vaccine were 27%-46% less likely to visit a health care provider because of flu and 40%-42% less likely to be hospitalized with flu.
- Vaccine effectiveness against influenza A(H1N1)pdm09 viruses was 25% for flu-related health care provider visits and 50% against flu-related hospitalizations.
- Adults who got a flu vaccine were 54% less likely to visit a health care provider for influenza A(H3N2).
For influenza B/Victoria lineage viruses, adults who were vaccinated were 78% less likely to visit a health care provider and 60% less likely to be hospitalized with influenza B/Victoria. (This is higher than has been typically observed during previous seasons.)

So far during 2023-2024, flu vaccination coverage among adults is similar to last season; however, disparities in flu vaccination coverage are sustained or worsening among people living in rural areas compared with those living in suburban or urban areas. Additionally, disparities by race and ethnicity persist, and Black adults continue to have the lowest vaccine coverage compared with all other racial and ethnic groups in the United States.

Older Adults

Adults 65 years and older who got a flu vaccine were 41%-51% less likely to visit a health care provider because of flu, and 42% less likely to be hospitalized with flu.

Specifically:

Against influenza A viruses, adults 65 years and older who got a flu vaccine were 40%-52% less likely to visit a health care provider for flu and 42%-47% less likely to be hospitalized with flu. Data by influenza A virus subtype for older adults are not available at this time.
Against influenza B/Victoria viruses, older adults were 69% less likely to visit a health care provider because of influenza B. (This is higher than has been typically observed during previous seasons.) There was not a large enough sample size to calculate vaccine effectiveness against hospitalization with influenza B/Victoria for older adults.

While flu seasons vary in severity, adults 65 years and older typically bear the greatest burden of severe flu disease. People 65 years and older are at higher risk of serious flu complications and usually also have a weaker immune response to vaccination. So far this flu season, vaccine effectiveness in older adults has been similar to younger adults. Similar protection among children and older adults has been seen during some previous seasons, especially against influenza A(H1N1) and influenza B viruses. However, this has not been consistent, especially for vaccine effectiveness against A(H3N2) viruses, which has been lower or in some cases with no measurable benefit observed. As a result, beginning with the 2022-2023 flu season, CDC and ACIP preferentially recommended the use of higher dose and adjuvanted flu vaccines for people 65 years and older. Comparisons between vaccine effectiveness for older adults this season with past seasons are difficult because of this preferential recommendation. Most adults 65 years and older included in the vaccine effectiveness studies received one of the preferentially recommended vaccines.

While flu vaccination coverage among adults 65 years and older remains higher than among younger adults, a decline in coverage in older adults has been seen since the 2020-2021 season. In 2020-2021, an estimated 75% of adults 65 years and older got a flu vaccine. At the end of last season (2022-2023), CDC estimated flu vaccination coverage among people 65 years and older to be 70%.

Get a Yearly Flu Vaccine for the Best Protection

Getting a yearly flu vaccine is the first and most important step in reducing the risk of flu illness and its potentially serious complications. Disappointingly, flu vaccination coverage among many groups of people has decreased significantly compared to before the COVID-19 pandemic. On the other hand, this report shows that for the most part, flu vaccines are working as well as, or better than, flu vaccines have in the past during seasons when vaccine viruses were well-matched to circulating flu viruses. This season, people who got a flu vaccine had a significantly reduced risk of a flu-related medical visit or hospitalization. Flu activity remains elevated nationally. There’s still time to get your flu vaccine if you haven’t already this season.

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