Head-to-Head Comparison Reveals mRNA Vaccines Behave Differently in Human Blood

In a scientific first, Australian researchers have carried out a direct head-to-head comparison of three mRNA-lipid nanoparticle vaccine platforms in human blood samples, uncovering striking differences in how the vaccines behave once they enter the bloodstream. The findings, published in ACS Nano, could reshape the design of future mRNA medicines, including the highly anticipated class of cancer vaccines now in development around the world.

The study, led by scientists at the Olivia Newton-John Cancer Research Institute (ONJCRI) and the Peter Doherty Institute for Infection and Immunity, analysed 327 blood samples from 73 participants who had received either the Moderna vaccine, the Pfizer vaccine, or an investigational COVID-19 mRNA vaccine. Rather than measuring immune responses, the team focused on something far more fundamental: what actually happens to the vaccine’s molecular cargo and its fatty delivery vehicle after injection.

mRNA-lipid nanoparticles, or mRNA-LNPs, are the tiny parcels that transformed vaccine delivery during the COVID-19 pandemic. Each particle is roughly 800 times smaller than the width of a human hair and is built from fatty acids, or lipids, that encase a payload of messenger RNA. This cargo carries the instructions cells need to produce a viral protein, triggering the immune response that generates protection against disease. Today, researchers worldwide are investigating mRNA-LNPs as candidates for cancer vaccines, which would deliver mRNA cargo designed to boost a patient’s immune system and empower it to kill tumours more effectively.

The research team assessed three critical properties across the different vaccine platforms: whether the mRNA cargo was present in the blood and remained intact after delivery, how stable the lipid-based packaging proved to be over time, and where along the mRNA molecule degradation occurred. These measurements provided an unprecedented molecular portrait of how each platform behaves in circulating human blood.

The results revealed that mRNA vaccines do not all behave the same way in the bloodstream. Dr Yi (David) Ju, senior author of the paper and laboratory head at ONJCRI, which is affiliated with La Trobe University as the School of Cancer Medicine, explained the central discovery. We found differences in how quickly their mRNA and lipid components declined, and how long sections of the mRNA remained intact, he said. In other words, the two commercially available vaccines and the investigational candidate each showed distinct kinetic profiles, with their genetic cargo and lipid envelopes degrading at different rates and in different patterns.

One of the most surprising findings concerned the integrity of the mRNA itself. The researchers discovered that much of the circulating mRNA measured in the Moderna and Pfizer groups was fragmented rather than whole. This means that by the time the vaccine’s genetic instructions could be detected in blood samples, a substantial proportion had already broken into pieces, a detail that had not previously been characterised in such detail in human recipients.

A more detailed analysis of samples from six Moderna recipients added an important layer of precision to this picture. The team found that the mRNA was less intact near one end of the molecule, a pattern that mirrored what was observed in the original vaccine formulation before injection. This suggests that some degradation may originate during manufacturing or storage rather than occurring exclusively inside the body, a clue that could prove invaluable for improving formulation stability across the entire supply chain.

According to the researchers, these findings provide strong clues on how to make the vaccines more stable. Greater stability would likely make the vaccines much more efficient, allowing patients to receive lower doses that cause fewer side effects while still generating a robust protective immune response. Because mRNA vaccines and therapeutics depend on intact RNA reaching the right cells at the right time, every improvement in cargo integrity translates directly into a more potent and better-tolerated medicine.

Prof Stephen Kent, first author of the study and laboratory head at the Doherty Institute, emphasised the broader significance of the work. These findings give us a way to compare the mRNA cargo and lipid delivery components of different vaccines in people, he said. That knowledge will help us design and evaluate future improved, more efficient mRNA vaccines and therapeutics, including approaches being developed for cancer. The comparison framework established in this study effectively gives researchers a standardised ruler for measuring how well any mRNA-LNP platform performs in the human body.

By establishing a framework to compare mRNA-LNP platforms directly in humans, the study opens a path toward rational, evidence-based improvement of mRNA-based medicines. As the field pivots from infectious disease toward cancer immunotherapy, where vaccines must coax the immune system into recognising and destroying tumour cells, understanding the fate of mRNA cargo in the bloodstream becomes more than an academic exercise. It becomes a blueprint for the next generation of vaccines, engineered to be more stable, more efficient, and gentler on the patients who receive them. The authors declared no competing financial interests, and the work stands as a landmark demonstration that even the most successful vaccines of the pandemic era still hold secrets worth uncovering.

Subject of Research: Comparative analysis of mRNA-lipid nanoparticle vaccine kinetics and transcript integrity in human blood samples

Article Title: mRNA vaccines compared head-to-head in world-first study

Article References: mRNA vaccines compared head-to-head in world-first study. (n.d.). Original publication

Image Credits: AI Generated

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Keywords: mRNA vaccines, lipid nanoparticles, cancer vaccines, vaccine stability, COVID-19 vaccines, ACS Nano, immunotherapy, vaccine design, mRNA degradation, Olivia Newton-John Cancer Research Institute, Doherty Institute, nanotechnology