Severe allergic reactions have been reported in only eight individuals who received Pfizer and BioNTech’s Covid-19 vaccine that raises some concern about its safety. Scientists believe that the compound used for the messenger RNA packaging (mRNA), i.e., polyethylene glycol (PEG), may be responsible to cause allergic reactions.
Previously, PEG was considered a biologically inert nanoparticle and has been used to develop many cosmetics and pharmaceutical products. Several studies have recently indicated that in very rare cases, drugs containing PEG may trigger anaphylaxis in very few individuals having a history of allergic reactions. Researchers have claimed that anaphylactic reactions can happen with any vaccine, but it is sporadic, i.e., about one per million doses. According to a report by the U.S. Centers for Disease Control and Prevention (CDC), among 272,001 people who received the Covid-19 vaccine, only six individuals reported anaphylactic reactions, as of 19 December 2020. Two similar cases have been reported in the United Kingdom.
PEG triggers the production of two groups of antibodies, namely, immunoglobulin M (IgM) and immunoglobulin G (IgG). Dr. Janos Szebeni, director at Semmelweis University, Budapest, believes that the allergic reaction to the Covid-19 vaccine is due to complement activation-related pseudoallergy (CARPA). CARPA is acute immune toxicity to nanoparticle-based medicines (e.g., PEGylated drugs) that the immune system incorrectly recognizes as a harmful agent such as viruses. During the clinical trials of Pfizer and Moderna mRNA vaccines, no adverse reaction was found.
However, Dr. Moein Moghimi, a nanomedicine researcher at Newcastle University, is not convinced that PEG is causing the allergic reaction and believes that a conventional mechanism is responsible. Other scientists have highlighted that the amount of PEG present in the mRNA vaccines, is much lower than the most PEGylated drugs.
Dr. Katalin Karikó, a senior vice president at BioNTech and co-inventor of the mRNA technology, stated that she had a prior discussion with Dr. Szebeni about the use of PEG and they agreed that intramuscular administration of the vaccine containing a meager amount of PEG would minimize the risk significantly. Karikó also said that all vaccines carry some risks, but the benefits far outweigh them.
According to the present CDC guidelines, Covid-19 vaccines developed by Pfizer and Moderna will not be administered to individuals with a history of severe allergic reactions to any component of the vaccine.
