Unlocking Enhanced Vaccine Efficacy: Stabilized Flu Proteins and Nanoparticle Technology for Improved Immune Response in Flu Vaccines

How Influenza Evades Immunity Through Shape-Shifting Proteins

Influenza viruses are relentless shape-shifters, constantly altering their surface structures to dodge human immune defenses. According to background details in the August 13, 2026 study, this evasion primarily targets critical proteins like hemagglutinin (HA), which governs how the pathogen attaches to and invades human cells. The virus achieves this through two main pathways: gradual mutation accumulation that obscures HA recognition, or reassortment events that swap out entire viral proteins and threaten to trigger global pandemics.

The global toll of this viral agility is staggering. Influenza causes up to 5 million cases of severe illness annually and claims between 290,000 and 650,000 lives worldwide each year, while four major pandemics since 1918 have caused tens of millions of deaths. For decades, standard commercial flu vaccines relied on traditional manufacturing methods involving chicken eggs. However, vaccine production is gradually shifting toward nucleic acids like mRNA—popularized during the COVID-19 pandemic—and advanced protein platforms that offer significantly greater flexibility, efficiency, and scalability.

The Structural Vulnerability of Hemagglutinin Trimers

On the outer envelope of every influenza virus, groups of three identical HA proteins assemble into bundles called trimers. These specific structures coordinate binding and subsequent entry into host cells. Because conventional vaccines train the immune system to spot these viral proteins, researchers must manufacture stable laboratory versions of the trimers. Unfortunately, native HA trimers are notoriously fragile, frequently misfolding or falling apart when exposed to standard temperature fluctuations or acidic environments.

“Influenza HA is naturally poised to change shape by design because it needs to undergo a dramatic structural change during viral entry,” explains Jiang Zhu, a professor at Scripps Research and senior author of the research. To combat this instability, Zhu’s team analyzed diverse flu viruses infecting humans, birds, and pigs, noticing a striking anomaly at the 95th amino acid position, which consistently displayed water-loving properties in an otherwise hydrophobic environment.

“At the core of the trimer, there are many oily residues that tend to group together. But then in the middle of this oily group, there’s one pretty big and disruptive water-like amino acid. So, I wondered, will the structure be more stable if we change this to an oily amino acid as well?”

By swapping that single water-loving amino acid for an oily one—specifically within the HA derived from the 2009 California pandemic strain—the researchers observed an immediate physical response. “It turns out, once you get rid of this troublemaker, specifically in the HA from the 2009 California pandemic flu strain, the structure suddenly closes and becomes more stable. That’s the magic trigger I’ve been looking for,” Zhu notes.

Engineering Stability and Next-Generation Nanoparticle Vaccines

Following this initial discovery, members of Zhu’s lab systematically substituted the water-loving amino acid at position 95 across multiple flu strains and compared their durability against naturally occurring HA trimers. Utilizing biochemical, biophysical, and structural testing methods, the team confirmed that the amino acid swap rendered the trimers significantly less prone to splitting apart across various strains, subtypes, and lineages, while also boosting stability in acidic conditions.

To refine the platform further, the researchers incorporated complementary stabilizing mutations. These included the “HKE” mutation designed by a team at Johnson & Johnson for certain influenza A viruses, alongside a related “NS” mutation optimized for influenza B viruses. Once a reliable stabilization framework was established, the team displayed up to 20 copies of these engineered trimers on Zhu’s proprietary SApNP technology. Preclinical evaluations in mice demonstrated that these nanoparticle-bound vaccines persisted in lymph nodes much longer than free-floating trimers, triggering notably stronger immune responses. Testing showed robust protection against identical viral strains, though cross-protection against different strains varied.

With ongoing efforts focused on developing universal vaccines that cross-protect against a broad spectrum of influenza viruses, this recent publication marks a major milestone. Having spent a decade crafting vaccine candidates using SApNP technology for targets including hepatitis C, Ebola and other filoviruses, RSV, and HIV, Zhu views this study as a capstone. “Publication of this research closes the chapter on a decade-long effort to design optimized antigens for representative virus families and display them on our self-assembling protein nanoparticles,” Zhu concludes, adding that the work represents a broader platform technology and development pipeline for structure-guided protein vaccines.