The nanoparticles in the Covid vaccine could trigger adverse reactions

mRna vaccines such as Pfizer's and Moderna's contain nanoparticles coated with Peg, a substance also used in other pharmaceutical and cosmetic products, against which the body sometimes produces antibodies

(photo: Leonardo Fernandez Viloria / Getty Images) What triggers some serious (but rare) adverse reactions to Pfizer and BioNTech's anti-Covid vaccine, among other things just approved in Europe? We don't know yet, but the world's leading experts are scrambling to find the answer, so that they can take all the necessary precautions. A hypothesis, already being examined by the National Institute of Allergy and Infectious Diseases (Niaid) and the United States Food and Drug Administration (Fda), is that the polyethylene glycol (Peg) nanoparticles surrounding the body are overexcited the immune system. mRna contained in the vaccine. Not everyone, however, agrees.

What is Peg

Polyethylene glycol, or Peg, is a polymer that finds many applications in the bio-pharmaceutical field. It is used in research for the production of monoclonal antibodies, but also in laxatives and in the formulations of other pharmaceutical products (from ointments to tablets) and in cosmetics, including toothpastes and shampoos. In short, it is considered a safe molecule.

Before now, however, it had never been used in a vaccine. Pfizer-BioNTech and also Moderna have instead introduced it in the composition of the brand new mRna vaccines against Covid-19: the mRna (i.e. the fragment of genetic material that serves to confer immunity) is wrapped in lipid nanoparticles (Lnp) chemically combined with the Peg. The Lnp serve to facilitate the entry of mRna into the cells while the Peg increases the stability and duration of the nanoparticles.

Anti-Peg antibodies

Until recently, Peg was considered an inert substance, that is, it does not react with biological systems. In recent years, however, scientists have found that the human body produces antibodies against it. A 2016 study reports that as much as 72% of people have some type of antibodies against Peg, perhaps due to the wide use made of them for cosmetics. Only in 7% of cases the presence of these antibodies would be high enough to predispose to the onset of anaphylactic reactions.

Not all studies on the subject, however, agree on the percentages. And if on the one hand there are companies that as a precaution have decided to eliminate pegylated molecules from their products, on the other there are experts who believe that such concerns are excessive.

Anaphylactoid reactions

It is not yet clear which immune mechanism may be involved. The antibodies against Peg would be of the IgM and IgG type, which do not give allergic and anaphylactic reactions (instead due to IgE).

Perhaps - some argue - other mechanisms are involved: non-specific immune responses that see the nanoparticles of Peg like viruses.

For others, however, there would not be a strong enough rationale to argue that Peg triggers exaggerated immune reactions to the vaccine: intramuscular injection would dilute the concentration of Peg in the blood over time , where most of the anti-Peg antibodies are found, making it irrelevant. More likely, however, that these are reactions linked to a hyper-reactivity of the local immune system of some people.

We need to investigate

The hypothesis that these strange adverse reactions to the Pfizer vaccine may be triggered by the PEG, however, is seriously considered by the US Niaid and the US FDA who have convened international experts and who intend to launch specific studies to verify this possibility.

It will take time, of course . Therefore, as both the CDCs and Pfizer and Moderna (who have not tested their respective vaccines on people with previous adverse reactions to pegylated pharmaceutical products) recommend, in the meantime it is best not to vaccinate those who have had a severe reaction to another vaccine or another injectable drug, and keep those who might develop an anaphylactic reaction under observation for about half an hour after administration, so as to be able to intervene immediately if it occurs.

In any case, for the moment, the plate of benefits still weighs much more than risks on the anti-Covid vaccine scale.

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