This year’s flu vaccination program is witnessing a significant change as the flu shot will now protect against three strains of the virus instead of the usual four. This adjustment comes after the Influenza B/Yamagata lineage has not been detected since the spring of 2020, leading health authorities to conclude that it no longer poses a threat to public health.
The Food and Drug Administration (FDA) made the decision to exclude the B/Yamagata strain from this year’s flu vaccine due to its absence over the past few years. The lack of confirmed cases has surprised many experts in the field of infectious diseases, as this marks a unique instance of a virus going extinct as a direct result of human behavior changes during the COVID-19 pandemic.
Dr. Rebecca Wurtz, an infectious disease physician and epidemiologist at the University of Minnesota School of Public Health, remarked on the significance of this development. She noted that the widespread physical distancing and mask-wearing during the early days of the pandemic played a crucial role in eliminating the B/Yamagata strain. This phenomenon is particularly noteworthy as it demonstrates how public health measures can impact viral circulation.
Dr. Kawsar Talaat, an infectious disease physician at Johns Hopkins Bloomberg School of Public Health, explained that before the pandemic, there was already a considerable level of immunity within the population against B/Yamagata. The strain had been circulating at lower levels, which contributed to its eventual disappearance. In contrast, the SARS-CoV-2 virus was entirely new to the human population, and while mitigation efforts reduced its transmission, they could not completely eradicate it.
Despite the absence of the B/Yamagata strain, the Centers for Disease Control and Prevention (CDC) continues to recommend the flu shot for everyone over the age of six months. The remaining strains, including B/Victoria and two lineages of influenza A, are still prevalent and capable of causing illness. Dr. Talaat emphasized that the disappearance of B/Yamagata does not equate to a reduction in the overall burden of flu, as the impact of different strains can vary significantly from year to year.
The CDC estimates that influenza is responsible for between 12,000 and 51,000 deaths annually in the United States, underscoring the importance of vaccination in protecting public health. The simplification of the vaccine to a trivalent formulation, targeting three strains instead of four, has streamlined the manufacturing process. This change allows for an increase in the production of flu vaccine doses, ensuring that more people can be vaccinated.
As the flu season approaches, health officials are urging individuals to get vaccinated, highlighting the critical role of flu shots in preventing illness and reducing hospitalizations. With the ongoing circulation of influenza viruses, vaccination remains a key strategy in safeguarding individual and community health.
In summary, this year’s flu shot will be a trivalent vaccine, marking a historic shift in the approach to influenza vaccination due to the extinction of the B/Yamagata strain. The public health response to COVID-19 has inadvertently shaped the landscape of influenza, providing valuable insights into the dynamics of viral transmission and immunity.
