Flu vaccines significantly reduced hospitalizations and emergency room visits during the 2024-25 influenza season, which experts considered the most severe since 2017-18. A new study led by researchers at the Centers for Disease Control and Prevention (CDC) found that vaccination protected both children and adults from serious illness requiring hospitalization or urgent outpatient care.

How Effective Were the Flu Shots This Season?

Scientists examined electronic health records from patients who visited seven medical centers across the United States between October 2024 and April 2025. The analysis included data from 5,764 pediatric hospitalizations, 102,854 pediatric emergency department and urgent care visits, 76,072 adult hospitalizations, and 233,411 adult outpatient visits.

The vaccine effectiveness varied by age group and type of medical encounter:

• Children's Protection: The vaccine was 51% effective at preventing flu-related hospital stays and 54% effective at preventing emergency department and urgent care visits in children ages 6 months to 17 years.
• Adults' Protection: In adults, vaccine effectiveness was 43% against hospitalization and 49% against emergency department and urgent care visits.
• Critical Illness Prevention: Vaccines also provided protection against the most severe outcomes, including intensive care unit (ICU) admissions in children and ICU admissions and deaths in adults.

Among the study population, only 17% of children and 28.2% of adults had received the flu vaccine, highlighting a significant gap in vaccination coverage.

Why Does Vaccine Protection Fade Over Time?

Researchers discovered an important pattern in how long the vaccine's protection lasted. The flu shot provided the strongest protection during the first two months after vaccination, after which immunity gradually declined. This finding suggests that timing of vaccination and potential booster strategies could be important considerations for future flu seasons.

"Seasonal influenza vaccination provided protection against influenza-associated hospitalizations and emergency department and urgent care encounters among US children and adults during the 2024-25 season," the authors wrote. "These findings support influenza vaccination as an important tool to reduce influenza-associated morbidity and mortality across the lifespan."

CDC-led research team, Open Forum Infectious Diseases

The 2024-25 season was particularly challenging because it was classified as severe, making the vaccine's protective effect even more meaningful. During severe flu seasons, hospitalizations and deaths increase substantially, so any reduction in these outcomes has significant public health value.

What Should People Know About Rapid Respiratory Virus Testing?

Beyond vaccination, new diagnostic tools are helping clinicians identify flu and other respiratory viruses more quickly. A pilot study in New Zealand primary care clinics tested multi-viral rapid-antigen point-of-care tests (MVRA-POCTs) that can detect COVID-19, influenza A and B, and respiratory syncytial virus (RSV) within minutes. Among 1,754 patients tested during winter 2023, 14% tested positive for at least one virus.

The rapid tests had practical benefits for both doctors and patients. Clinicians reported that 63% of prescribers said the test results influenced their antibiotic prescribing decisions, helping reduce unnecessary antibiotics for viral infections. Additionally, 12% of clinicians used the results to guide decisions about referring patients to secondary care.

Patient response was overwhelmingly positive. All patients who tested positive and 96% of those who tested negative said they would want the rapid test available in future visits. Notably, patients who received a positive test result reported being more likely to follow non-pharmaceutical interventions like isolation and mask-wearing to reduce disease transmission.

"MVRA-POCTs were well-accepted and readily incorporated into practice. Routine integration into primary care could potentially improve management of common respiratory illnesses and promote patient behaviour change to reduce transmission," the researchers concluded.

New Zealand Primary Care Research Team, BJGP Open

The combination of vaccination and rapid diagnostic testing represents a two-pronged approach to managing respiratory viruses. While vaccines prevent infection and severe disease, rapid tests help clinicians make faster, more accurate treatment decisions and encourage patients to take steps to protect others.

Public health experts emphasize that the 2024-25 flu season underscores the importance of vaccination, particularly for vulnerable populations including young children, older adults, and people with chronic health conditions. The CDC-led study provides concrete evidence that despite the season's severity, vaccination remained an effective tool for preventing serious illness.