This past Thursday and Friday, the Centers for Disease Control and Prevention (CDC) convened a meeting of its Advisory Committee on Immunization Practices (ACIP), a pivotal group providing guidance to the CDC director regarding vaccine recommendations for the public.
Ultimately, the panel decided to delay its most contentious vote while making recommendations that could raise doubts about the safety of Covid-19 vaccines, despite their continued availability. Several presenters and panelists voiced concerns over potential unverified safety issues regarding mRNA Covid vaccines developed by Moderna and Pfizer/BioNTech.
One prominent voice of concern was Retsef Levi, chair of ACIP’s working group on Covid vaccines. He highlighted apprehensions that mRNA, the lipid nanoparticles used for encapsulation, and the spike protein induced by the vaccines might persist within the body and provoke an immune response that is not fully understood. Both Moderna and Pfizer have countered these claims, asserting that they have been debunked by thorough studies adhering to global regulatory standards.
In an interview with Drew Weissman, a professor at the University of Pennsylvania and co-recipient of the 2023 Nobel Prize in Physiology or Medicine for his contributions to mRNA vaccine technology, STAT inquired about these claims. Below, we present an edited version of that conversation for clarity.
At the recent ACIP meeting, there was much discussion about whether mRNA is distributed widely throughout the body or has a prolonged presence.
There are studies suggesting a range of viewpoints—including erroneous claims like the Earth being flat and DNA being non-double stranded. However, the overwhelming consensus is supported by thousands and millions of robust papers that debunk such outlandish assertions.
Some critics isolate a singular paper or two that make extreme claims based on flawed data, ignoring the multitude of studies that contradict them. For instance, they might cite a study claiming the spike protein remains in the body for nine months, which simply isn’t true. Many reputable studies indicate that the RNA from the vaccines is eliminated from the body within days. It does not reach the brain or eyes. Studies that injected massive doses of RNA into mice created a different scenario, leading to widespread distribution. In contrast, at vaccine-equivalent doses, we see RNA localized primarily in the muscle and nearby draining lymph nodes.
What about concerns regarding the ongoing production of spike protein? For example, there’s the preprint authored by Akiko Iwasaki, which includes respected researchers from Yale and indicates residual spike protein.
Unfortunately, that study utilized a flawed assay for measuring spike proteins. Although their assay is ultra-sensitive, it is prone to errors. Researchers must only believe data that exceeds a certain threshold to be considered real. What they found fell within an ambiguous range, possibly mere noise rather than actual spike. Many other studies employing validated methodologies have not detected circulating spike proteins.
(In late August, Iwasaki communicated to STAT: “We have already conducted two distinct approaches to measure spike proteins and are now refining methods to enhance sensitivity and accuracy for validation.”)
How confident are you that mRNA is not widely disseminated in the body?
I am certain it is not broadly distributed. We demonstrated this back in 2017 with vaccine doses, analyzing various animal models—including mice, macaques, and rabbits—as well as human data. We have not observed RNA circulating in areas like the placenta, testes, heart, eyes, or brain, which are often raised as concerns. Many researchers have investigated these questions, and the evidence remains consistent: we do not see widespread RNA distribution.
It’s improbable, then, that a single mRNA dose could continue producing spike proteins for months in rare individuals?
That is absolutely impossible. mRNA is rapidly degraded. Even modified forms last around 24 hours but never extend to six months. Claims to the contrary result from the misuse of specific assays leading to inaccurate conclusions.
I would like to cite particular concerns raised by Dr. Retsef Levi about “wide biodistribution and prolonged persistence of spike proteins, mRNA, and nano-lipid particles.” He also mentioned unverified prolonged immune responses.
While rare, prolonged immune responses do mainly occur in immunized mice. Although we can find human cases with varying responses, they remain infrequent.
Another issue discussed was a potential “frameshift leading to unintended protein production,” which suggests the vaccine alters how DNA constructs proteins.
That was based on a single paper alleging that uridine caused frameshift mutations, but no evidence supporting this has been found in countless other studies.
What about concerns regarding DNA contamination in vaccines? Some assert that DNA impurities are present at unacceptably high levels, and that the lipoprotein facilitating mRNA delivery could lead to their uptake.
DNA contamination is virtually universal in vaccines—stemming from their production in living cells or eggs. When purifying vaccines, low levels of DNA are common, but we’ve never observed associated adverse events. The contaminations from mRNA vaccines are minuscule, typically comprising just a couple of nucleotides. Integration into genomic DNA or inducing cancer has not been documented.
Is there anything else you’d like to add?
What worries me the most from these recent meetings is their dismissal of recommending combined childhood vaccinations. They have turned down proposals to expand Covid-19 vaccine availability and are likely to vote against administering hepatitis B vaccinations to infants as well.
Looking back at the evidence, it’s clear that 250 years ago, 40% of children did not survive to adulthood—today that figure stands at merely 4%. Vaccines are responsible for this dramatic improvement, saving lives more than any other medical intervention, including antibiotics. The mRNA vaccines underwent more rigorous testing than any other, were administered to more individuals than any other vaccine, and were proven exceedingly safe, outpacing the safety of other platforms. They have reportedly saved 20 million lives and played a crucial role in halting a pandemic that disrupted the globe.
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