When genomic scientist Kevin McKernan discovered excessive levels of residual DNA in mRNA Covid vaccines, it sparked one of the fiercest safety debates of the pandemic.
Regulators insisted the fragments were present only in trace amounts and posed no biological risk, while critics warned they could potentially trigger autoimmune diseases or integrate into the human genome and contribute to cancer.
But the row overshadowed a far broader problem.
mRNA vaccines are not the only products made using recombinant DNA technology. Manufacturers also use it to produce vaccines against hepatitis B, human papillomavirus, shingles and influenza, as well as monoclonal antibodies given to infants to prevent RSV.
All of these products can carry residual DNA from the manufacturing process, yet fundamental questions about what happens to those fragments after injection remain largely unanswered.
This years-long investigation—built on internal company documents, regulatory filings, court records, and scientific interviews—points to a deeper issue.
Residual DNA may not be just a benign impurity. It can have adjuvant activity, stimulating the immune response and potentially boosting a vaccine’s efficacy.
Consequently, removing the impurity might also compromise its performance—a dilemma that may prove to be the vaccine industry’s dirty little secret.