mRNA vaccines are considered one of the most significant biomedical developments of recent years. Billions of doses have been administered worldwide, while numerous additional mRNA-based applications are currently under development – ranging from cancer immunotherapies to vaccines against a wide variety of infectious diseases.
The public discussion over residual DNA in mRNA vaccines did not begin with a regulatory announcement or official safety warning, but rather somewhat coincidentally in the course of molecular biology sequencing work.
In early 2023, a research team led by the U.S. geneticist Kevin McKernan was working on RNA sequencing experiments that required highly purified RNA samples. As part of this work, the team used unopened vials of the COVID-19 vaccines produced by BioNTech/Pfizer and Moderna. During the analyses, the researchers came across an unexpected finding: in addition to the modified mRNA, DNA sequences were also detected in the samples.
It is well known in the pharmaceutical industry – and taken into account by regulators – that small amounts of residual DNA can technically occur in certain biotechnological manufacturing processes. What was surprising, however, was that at that time there had been little public discussion about which manufacturing processes were actually being used for large-scale production and to what extent independent analyses of the final products were available at all.
Subsequent studies by McKernan and other research groups ultimately reported the presence of residual DNA in various vaccine batches – in some cases in amounts that, according to the authors, exceeded regulatory guidelines. This sparked a scientific debate that continues to this day.
But what exactly is this all about?
The public debate quickly focused on seemingly simple questions:
Are there residual DNA – or not?
Are regulatory limits being met?
And if DNA is detectable, what biological significance would that actually have?
However, on closer examination, it becomes clear that these questions are analytically much more complex than they first appear.
This is because the production of modRNA-based vaccines is already a multi-step process in which bacterial DNA templates are technically indispensable. The removal of this DNA is part of the standard purification steps in manufacturing. However, complete molecular separation in biological production processes is rarely a purely binary matter. What matters instead is:
Which fragments might remain in the final product?
In what quantity?
With what structure?
And above all:
What methods can be used to measure this reliably at all?
The debate garnered additional attention following the public disclosure of discrepancies between early development methods and later large-scale industrial production. While comparatively small amounts of DNA were amplified in early clinical development phases using PCR-like methods, bacteria-based manufacturing processes were used for the subsequent billion-dose production. These processes are industrially well established and enable large-scale output, but they also come with more complex requirements for purifying biological residual components.
It was precisely this transition between different production processes that was later the subject of intense debate – partly because a large portion of the early clinical trials had still been conducted using vaccine batches produced via the original manufacturing process.
There is also another issue: The detection of residual DNA depends strongly on the methodology used.
Different laboratory groups used different digestion methods, extraction methods, PCR designs, and sequencing approaches – with results that in some cases differed significantly from one another. The discussion therefore concerns not only the measured values themselves, but also the question of how reliable and comparable these measurements actually are.
This two-part series of articles therefore does not attempt to provide hasty answers. Instead, its aim is to make the scientific and methodological background underlying the current debates understandable.
The first part describes the manufacturing and purification processes of modRNA-based vaccines:
How is the mRNA produced?
Why are bacterial DNA templates needed?
What byproducts are generated during production?
And what methods are used to remove unwanted residual components?
The second part then focuses on the analytical perspective:
How can residual DNA be detected in the first place?
What is the interpretive value of qPCR, Qubit, or sequencing methods?
Why can different measurement techniques lead to different results?
And what do the independent studies published to date actually show?
It becomes clear that a distinction must be made between analytical detection and biological assessment. Many questions are still scientifically unresolved – such as the native fragment distribution of residual DNA, the possible role of RNA, or the biological relevance of specific sequence elements under real physiological conditions.
This is precisely why the debate ultimately touches on a fundamental scientific question:
How does modern biomedicine deal with uncertainty, detection limits, and methodological complexity – especially in the context of novel biological technologies?
The following two parts are intended as an invitation to consider these questions in a nuanced way: not as a headline, but as a scientific problem whose assessment requires precision, transparency, and methodological understanding.
This presentation aims to bridge the gap between often highly technical academic publications and simplified media reports, so that even interested non-specialist readers without prior expertise can follow the complex interrelationships.
The text does not claim to be exhaustive – it strives for objectivity, accuracy, and fairness toward all perspectives involved.
About the article series
The analysis is divided into two parts that build on each other thematically. Both can be read independently; however, for a comprehensive understanding, the suggested order is recommended.
Part 1: Production and Purification
Table of Contents – Part 1
1. Manufacturing Processes – An Overview
1.1. Product Formation – From Gene to mRNA
1.2. Impurities and Byproducts
1.3. Purification Methods in the Manufacturing Process
1.4. Comparison: Process 1 vs. Process 2
1.5. Summary: Production and Purification of modRNA
Part 2: Detection Methods and Current Evidence
Table of Contents – Part 2
2. Methods for Measuring DNA and RNA
2.1. Spectrophotometric Methods
2.2. Fluorescence-based Quantification
2.3. Amplification-based Methods
2.4. Sequencing-based Methods
2.5. Electrophoretic Fragment Analysis
2.6. Comparison of Key Detection Methods for Nucleic Acids
3. Guidelines for Limiting Residual DNA in Vaccines
4. Studies on Residual DNA in modRNA-based Vaccines
4.1. Why Independent Measurements?
4.2. Methodological Remarks
4.3. Overview and Individual Analyses of the Studies
4.4. Interim Conclusion: What do we know — and what do we not know?
5. Conclusion and Outlook
Current as of June 2026.
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