Endorsement for New Flu Strain Inclusion in Upcoming Vaccines
Even though the U.S. is no longer a part of the World Health Organization, American scientists continue to work with global researchers to monitor the development of influenza viruses.
In a recent development, a unanimous approval was given by an advisory committee on vaccines for the inclusion of recommended viral strains in fall flu shots. The final say, however, lies with the head of the organization that regulates food and drugs.
Introduction of a New Variant
Members of the committee gave the green light for the inclusion of a new strain, called A(H3N2) subclade K, in the fall flu vaccines. This strain made its first appearance in October, and although it was too late to be included in last year's vaccines, it has become the prevalent flu variant in the Northern Hemisphere, as informed by a flu expert at the national center for disease control.
The decision-making process concerning the annual flu shots has to take place in February or March, given the six-month time frame required to manufacture and distribute the vaccines using current technology.
Flu Viruses and Their Rapid Mutation
In a recent meeting, experts from the disease control center presented the genetic components of current flu viruses, based on samples collected worldwide. However, flu viruses are known to mutate rapidly, meaning there is no certainty that the three variants chosen today will be the ones spreading in the next fall and winter season.
"It's a combination of science and luck," said the acting chair of the advisory committee and a professor of public health and epidemiology.
Less Effective Vaccines this Year
The difference in strains is one of the reasons why this year's flu vaccines were less effective than usual. Based on interim results from three surveillance networks, it was found that vaccination reduced the number of flu-related outpatient visits among children by 38% to 41% and decreased their hospitalization risk by 41%.
For adults, the effectiveness of the vaccine in preventing outpatient visits and flu-related hospitalization was found to be 22% to 34% and 30% respectively. Separately, it was reported that the vaccine's effectiveness against lab-confirmed flu for all age groups was 33% (32% against influenza A and 47% against influenza B).
Heavy Impact on Young People
The flu has had a severe impact on young individuals in recent times, leading the disease control center to categorize this season as "high severity" for children. Approximately 90 children have succumbed to the flu, with around 85% of eligible children not being fully vaccinated. For adults, the flu season has been moderate. Among adults age 65 and older, flu vaccines reduced flu-related medical visits by 22% to 34% and hospitalizations by 30%.
The current flu season has seen the third-highest number of flu-related hospitalizations since the 2010-11 season, and the second-highest among children. A shift is being observed in the types of flu being treated, with fewer cases of influenza A and an increase in influenza B.
Since October, the flu has caused up to 42 million illnesses, up to 19 million medical visits, up to 660,000 hospitalizations, and up to 66,000 deaths, as per estimates.
Decrease in Flu Vaccination Rates
Since the onset of the COVID-19 pandemic, flu vaccination rates have seen a decrease. The number of flu vaccines distributed each season has dipped by 23% since the 2019-20 season. This season, manufacturers distributed 134.6 million flu doses.
Following recommendations, the advisory committee suggested that all three viral strains be replaced for next fall's flu vaccines. The specific recommendations for inclusion in this year's flu shots include:
- An A/Missouri/11/2025 (H1N1)pdm09-like virus
- An A/Darwin/1454/2025 (H3N2)-like virus
- A B/Tokyo/EIS13-175/2025 (B/Victoria lineage)-like virus
These recommendations apply to egg-based vaccines. However, for cell culture-, recombinant protein-, or nucleic acid-based vaccines, different strains may be suggested.