Research shows that flu shots have significantly reduced visits to doctors and hospitalizations due to influenza this season. (Photo by Witthaya Prasongsin via Getty Images)
According to preliminary data, this year, influenza vaccination has significantly reduced the number of hospitalizations associated with seasonal influenza.
For children and adolescents, the vaccines were at least 63% effective against flu-related hospitalizations, and up to 78% effective in some areas. The data came from two health care networks that the Centers for Disease Control and Prevention (CDC) uses to evaluate the effectiveness of flu vaccinations.
“Vaccine effectiveness” measures how much a vaccine reduces the likelihood of a particular health outcome in real-world settings, and is calculated by comparing the incidence of that outcome among vaccinated and unvaccinated people. So in this case, vaccinated children were 63% to 78% less likely to be hospitalized for influenza.
For people over 18 years of age, the vaccines demonstrated effectiveness against hospitalizations of 41% and 55%, respectively, in the two networks.
The vaccines also reduced the likelihood of influenza-related outpatient visits to the doctor, including routine consultations as well as urgent care and emergency department visits. For children and adolescents, the effectiveness was 32%, 59%, and 60% across three networks, while for adults, it was 36% and 54% across two networks.
These estimates, released Thursday (Feb. 28) in the Morbidity and Mortality Weekly Report (MMWR), are subject to change as the flu season progresses.
At first glance — compared with estimates provided for flu shots last season at this time last year — the 2024-25 vaccines appear to provide greater protection against childhood hospitalizations. However, they may be less effective against outpatient visits for some children. Meanwhile, adult protection appears to be slightly higher for both types of care this season.
“The results of this report indicate that influenza vaccination for 2024–2025 reduced the likelihood of influenza requiring medical intervention and support CDC’s recommendation to vaccinate all persons aged ≥6 months against influenza,” the MMWR noted.
“These data also support a significant protective effect of influenza vaccination against influenza-associated hospitalizations, highlighting the importance of vaccination to reduce more serious complications associated with this disease,” the study concluded.
The MMWR authors suggested that a flu subtype known as H3N2 could explain why vaccinations have not provided sufficient protection in outpatient visits among children this season.
Flu viruses in humans fall into two main types — classified as either “A” or “B” — which are then divided into subtypes and variants. CDC data shows that the vast majority of flu cases this year are caused by influenza A viruses. Scientists have genetically analyzed a subset of these A viruses and found that they fall into two subtypes: H1N1 and H3N2.
Nationally, H1N1 and H3N2 account for about half of influenza A cases. However, the ratio of H1N1 to H3N2 varies by region and therefore by network. The MMWR suggests that vaccines were less effective against outpatient cases in children in areas where H3N2 was more prevalent. Laboratory studies with ferrets have already shown that vaccines were not as good “matches” for circulating H3N2 viruses as they were for H1N1 viruses.
However, this season's flu shots show protection levels “consistent with those seen in the 2023-24 season and seasons associated with higher vaccine efficacy over the past 15 years,” the MMWR reports. The flu season in the United States could last until May, so it's not too late to get a flu shot.
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Sourse: www.livescience.com
