DNA Contamination in Pfizer and Moderna Covid Vaccines

The mRNA vaccine technology (Riggs, 2021)

Published: November 2023

Newly discovered DNA contamination in Pfizer and Moderna covid vaccines: a global pharmaceutical scandal or much ado about nothing?

Previous covid vaccine quality issues

The newly discovered DNA contamination in Pfizer and Moderna covid vaccines, which will be discussed in detail below, is not the first instance of covid vaccine quality issues.

Already in late 2020, hacked and leaked data from the European Medicines Agency (EMA) revealed that mRNA molecule integrity in commercial batches of the Pfizer covid vaccine was significantly lower than required: only about 50% instead of about 80% of mRNA molecules were intact. Nevertheless, EMA approved the vaccine and didn’t notify the public.

In early 2021, US pharmaceutical company Emergent BioSolutions (EBS) was found to have serious manufacturing issues that caused the contamination of millions of doses of J&J and AstraZeneca covid vaccines. US authorities stopped the sale of all EBS-produced vaccine doses in the United States but allowed the exportation of “clean doses” to neighboring Canada and Mexico.

In August 2021, Japanese health authorities found that some batches of the Moderna covid vaccine were contaminated with a “metallic substance” and recommended “to be on the watch for possible health problems” if one had received a Moderna vaccine dose. This unfortunate episode once again spurred untrue rumors on social media that covid vaccines contained toxic “graphene oxide”.

In early 2023, an investigation by Danish researchers found that some batches of the Pfizer covid vaccine were responsible for a disproportionate number of reported adverse events, while other batches didn’t result in any reported adverse events. Such an imbalance may indicate differences in vaccine quality, but it could also be due to different batch sizes and recipients.

The Danish researchers could not resolve this question because the vaccine manufacturer and national regulators did not release the necessary data. The head of epidemiology research at the Danish State Serum Institute argued in a response that the observed differences were mostly due to the size and timing of vaccine batches (early batches were small, late batches not yet used).

DNA contamination in Pfizer and Moderna vaccines

In the spring of 2023, a US genomics expert found that Pfizer and Moderna covid vaccines contained billions of fragments of so-called plasmid DNA arising from the industrial-scale bacterial production process of these vaccines. These findings have since been confirmed by other researchers from Germany and the US, including by a professor at the University of South Carolina.

Vaccine skeptics and some genomics experts have expressed concerns that these plasmid DNA fragments might pose a health risk. The main concern is that plasmid DNA fragments might integrate into cellular DNA and modify the genome of affected cells, which in turn might increase the risk of cancer, autoimmune diseases, and other long-term adverse events.

This concern is heightened by three factors: first, unlike mRNA contained in covid vaccines, the DNA fragments do not require reverse transcription to integrate into the genome; second, while “naked” DNA is quickly degraded, the use of nanolipids in mRNA vaccines might enhance the transfer of DNA fragments into cells; and third, DNA fragments found in the Pfizer vaccine contain the notorious SV40 “monkey virus” promoter sequence, which might enhance DNA integration and expression.

In recent weeks, several health agencies, including the US FDA, the European EMA and Health Canada, have acknowledged the presence of these plasmid DNA fragments. However, the agencies emphasize that the presence of these residual DNA fragments was already known (to them); that their amount is usually below current regulatory limits (for “naked” DNA); and that there is no evidence that these DNA fragments pose any health risks anyway.

It has also been pointed out that other vaccines – such as the live-attenuated chickenpox vaccine, adenoviral vector vaccines (such as the AstraZeneca covid vaccine), or actual DNA plasmid vaccines (such as the Indian ZyCoV-D covid vaccine) – contain more DNA than the residual DNA found in Moderna and Pfizer mRNA covid vaccines. While true, this will hardly convince skeptics.

Some health agencies have acknowledged that they were not aware the plasmid used by Pfizer contained the SV40 promoter sequence (the sequence is “visible” in the genetic code but wasn’t highlighted or annotated by Pfizer). Yet the agencies argue that this doesn’t really matter since the promoter sequence is not a bioactive vaccine ingredient anyway.

This point is disputed by some genomics experts. The SV40 promoter sequence obviously is a bioactive component of the plasmid itself: its role is to boost the expression of a plasmid gene for antibiotics resistance that supports bacterial growth and selection during the vaccine manufacturing process. Whether residual DNA fragments containing the SV40 promoter sequence are still bioactive in the Pfizer vaccine remains an open question (see concern #3 above).

The cancer question

Back in the 1950s, early batches of the newly developed polio vaccine were contaminated with the SV40 monkey virus, a virus that in some cases can cause cancer. However, it was never established that the contaminated polio vaccines did in fact cause any cases of cancer. Furthermore, the current Pfizer covid vaccine isn’t contaminated with the SV40 virus, but only with fragments of its promoter sequence, which by itself isn’t known to cause cancer.

Health agencies are correct that there is currently no evidence of any unusual increase in cancer cases or cancer-related deaths. Some case studies of unusual post-vaccination tumor growth do exist, however, and some cancer specialists keep reporting unusual cases of post-vaccination or post-booster cancer. Such cases, if they are at all linked to covid vaccination, have sometimes been attributed to transient post-vaccination immune suppression or immune dysregulation.

In addition, in some states there appears to be an unexplained increase in certain types of cancer, such as lymph node cancer. Lymphadenopathy (enlarged lymph nodes) is a well-known and rather frequent adverse event of covid mRNA vaccination: about 10% of people who received a Moderna booster were affected. Post-vaccination lymphadenopathy is likely due to an inflammatory response and may be linked to the IgG4 antibody switch observed after repeated mRNA vaccination.

Clinical trial doses vs. commercial doses

Can the large covid vaccine trials run in 2020 help answer questions concerning the health effects of residual DNA fragments? The answer is no, and this is not just because these trials stopped their follow-up phase prematurely and appear to have suppressed adverse event reporting.

As one Israeli researcher pointed out, the DNA contamination and its potential clinical significance could not be identified during the vaccine trials in 2020 because Pfizer and Moderna used different manufacturing methods for trial batches and for commercial batches.

While the mRNA in clinical trial doses was synthesized in a direct and clean PCR lab process, the mRNA in commercial doses was produced in an industrial process that used bacterial DNA plasmids. Only the industrial manufacturing process resulted in DNA contamination and reduced mRNA integrity (as previously revealed in the hacked EMA files discussed above).

In fact, according to the Israeli researcher, Pfizer tested the commercial vaccine doses on only 250 people prior to their global distribution and never performed or published the required safety and efficacy comparison between trial batches and commercial batches.

Vaccines or gene therapy?

The DNA contamination issue has also reignited the old “vaccine vs. gene therapy” debate:  most health authorities still insist that covid mRNA vaccines are vaccines and not gene therapy, while many vaccine skeptics argue that they are gene therapy and not vaccines.

But as SPR noted already back in December 2021, this was one of the many misguided covid debates, since covid mRNA vaccines are both vaccines and gene therapy at the same time. Debating whether they are vaccines or gene therapy is like asking if a red car is red or a car.

It is true, however, that health agencies in 2020 excluded covid mRNA vaccines from the strictly regulated category of gene therapy products (GTPs) to speed up their development and approval process – which is why some “fact-checking organizations” could claim they weren’t GTPs.

Like most types of “gene therapy”, covid mRNA vaccines aren’t intended to alter the genome, and there is still no evidence that they have done so. The presence of plasmid DNA fragments might increase the risk of genome integration since DNA doesn’t require reverse transcription, but as previously mentioned, there is not yet any evidence that integration did in fact occur.

Covid mRNA vaccines: success or failure?

Many skeptics view covid mRNA vaccines as a complete failure, while many vaccine promoters view them as a huge success. Thus, many skeptics cannot understand why two mRNA vaccine pioneers recently won the Nobel Prize in Medicine and why pharmaceutical companies want to expand the use of mRNA products, while many promoters believe mRNA will revolutionize medicine.

The fact of the matter is that covid mRNA vaccines were indeed very successful in reducing covid mortality and restoring life expectancy in 2021. However, protection against infection and transmission waned within weeks; protection against severe disease and death waned significantly within six to twelve months; the likely synthetic omicron variant further degraded protection after just one year; updated boosters proved rather ineffective; the safety profile was rather poor, especially for young people; and potential long-term health effects remain unknown.

At the purely immunological level, covid mRNA vaccines were successful in producing a strong initial antibody response, but the immunity they provided proved to be rather short-lived. The initial hopes that mRNA vaccines would be quicker to develop and easier to adapt to new variants were not fulfilled: some traditional types of vaccines were developed and approved just as quickly and antigenic priming largely frustrated attempts to “update” covid vaccines.

Many former zero-covid countries that used mRNA vaccines have achieved a clear mortality advantage but no complete victory over other Western countries. This result was influenced by vaccine-escaping yet milder omicron variants, though: without vaccine-escaping variants, the success of zero-covid countries would have been complete, but with a deadlier vaccine-escaping variant (such as a delta plus variant), their advantage would have evaporated.

Thus, the long-term success of the mRNA technology in the field of vaccines and other medical fields remains an open question at this point in time. If it turns out that covid vaccine adverse events were caused not just by the notorious coronavirus spike protein, but by the mRNA core technology or the pro-inflammatory nanolipids, or if any long-term issues do materialize, mRNA biotechnology may ultimately be seen as a failed experiment.


The potential pharmaceutical and clinical effects of the newly discovered plasmid DNA fragments in Pfizer and Moderna covid vaccines need to be investigated very carefully. Vaccine promoters who claim the long-term safety of covid vaccines has already been established are just as wrong as vaccine skeptics who claim the global covid vaccine apocalypse is a certainty.

A worst-case scenario, comparable to Merck’s Vioxx scandal or Johnson&Johnson’s asbestos-laced baby powder, remains a possibility but has not yet materialized. Such a worst-case scenario could be caused by widespread cardiovascular, oncological, or other long-term adverse events.

Covid mRNA vaccines have already caused heart issues in about one in one thousand young males, including competitive athletes, whose long-term health outlook remains rather uncertain. The 1976 swine flu vaccine, which caused 500 cases of Guillain-Barré syndrome, and the 2009 swine flu vaccine, which caused narcolepsy in children, were eventually both taken off the market.

Health agencies who have approved covid vaccines and whose executives are often linked to the pharmaceutical industry may not be overly eager to investigate potential health issues. Because of this, the work of qualified independent investigators remains of utmost importance.

The detection of residual DNA fragments once again indicates that the production and approval process of covid vaccines was rushed and that they should never have been given to people not at risk of severe or fatal covid, as emphasized by Swiss Policy Research since early 2021.

You have been reading:

DNA Contamination in Pfizer and Moderna Covid Vaccines
An analysis by Swiss Policy Research.

Annex: The plasmid used for the Pfizer covid vaccine


Pfizer plasmid DNA analysis (McKernan 2023)

Video collection

Read more

Share on: Twitter / Facebook


Up ↑