Potential impact of changes in influenza vaccination coverage and effectiveness on pediatric influenza burden in the United States, 2022/23-2024/25

Every year, seasonal influenza sweeps through communities, causing a wide range of illness from mild fevers to severe pneumonia. While many people recover quickly, the virus poses a significant threat to children, leading to thousands of hospitalizations and hundreds of deaths across the United States annually. To protect against this, health officials recommend an annual flu shot for everyone six months and older. The vaccine works by training the body's immune system to recognize and fight the virus, a process that has been proven safe and effective for decades. However, the protection a community receives depends on two main factors: how many people get the shot, known as vaccination coverage, and how well the shot matches the circulating virus, known as vaccine effectiveness. When coverage drops, the shield around the population weakens, leaving more children vulnerable to severe outcomes.

Researchers at the Centers for Disease Control and Prevention recently examined what happened to children during three recent flu seasons, from 2022 through 2025, a period when vaccination rates among children had fallen below previous highs. They wanted to understand the true cost of this decline. Using a computer model that simulates how the virus spreads and causes illness, the team reconstructed the burden of disease during these years based on actual hospital records and vaccination data. They then ran a series of simulations to see what would have happened if more children had been vaccinated or if the vaccines had worked slightly better. The goal was not to rewrite history, but to measure the potential difference that higher vaccination rates could have made in preventing hospitalizations and saving lives.

The analysis began by tallying the real-world impact of the flu during the 2022/23, 2023/24, and 2024/25 seasons. The researchers estimated that across these three years, approximately 120,000 children between the ages of six months and 17 years were hospitalized due to influenza, and about 1,650 children died. The 2024/25 season was particularly severe, accounting for the highest number of deaths and hospitalizations in that period. The team then tested different scenarios to see how the numbers might have changed. In one scenario, they imagined if vaccination coverage had increased by just five percentage points across the board. In another, they imagined if the vaccines themselves had become five percentage points more effective at preventing illness. They also combined these two improvements and, finally, they simulated what would have occurred if vaccination rates had returned to the levels seen in the 2019/20 season, which was the peak of pediatric vaccination coverage in recent years.

The results of these simulations offered a clear picture of the potential benefits of higher vaccination rates. When the researchers increased vaccination coverage by five percentage points, they estimated that the number of hospitalizations would have dropped by about 3.1 percent, and deaths would have fallen by 3.2 percent. This translates to roughly 3,770 fewer hospitalizations and 54 fewer deaths across the three seasons. Improving the effectiveness of the vaccine by the same margin yielded a nearly identical result, suggesting that either factor alone could have made a meaningful difference. When they combined both improvements—raising coverage and effectiveness by five percentage points each—the reduction in hospitalizations grew to 6.6 percent, and deaths dropped by 6.7 percent.

However, the most significant impact came from the scenario that restored vaccination rates to their 2019/20 levels. In this simulation, the model predicted that 8,670 fewer children would have been hospitalized and 130 fewer children would have died across the three seasons. This represents a reduction of 7.2 percent in hospitalizations and 7.9 percent in deaths. The researchers noted that the 2019/20 season had the highest vaccination rates on record, with 76 percent of young children and 60 percent of older children receiving the vaccine. Since then, rates have declined, with only 58 percent of young children and 48 percent of older children vaccinated in the 2024/25 season. The study highlights that the drop in coverage coincided with a period of high severity, particularly in the most recent season, which saw a record number of pediatric flu deaths.

The authors emphasized that their findings are based on simulations using available data, which means the exact numbers of prevented cases are estimates rather than direct measurements. The model accounted for how many children were vaccinated and how well the vaccine worked in different age groups, but it did not include the indirect benefits of vaccination, such as the reduced spread of the virus from vaccinated children to others. Despite these limitations, the trend was consistent: higher vaccination coverage consistently led to fewer severe outcomes. The study suggests that the decline in vaccination rates over the last few years likely contributed to the high number of severe cases and deaths observed. By returning to the higher coverage levels achieved in 2019/20, the public health system could have significantly reduced the burden of influenza on children, preventing thousands of hospitalizations and saving over a hundred lives. This work underscores the importance of maintaining high vaccination rates as a primary defense against seasonal influenza, especially for the youngest and most vulnerable members of the population.