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It's Not the Vicar's Fault!
Published in Norman Begg, The Remarkable Story of Vaccines, 2023
A major source of anxiety about vaccine safety is that they contain chemicals that are perceived to be harmful. The reality is that these chemicals are either not present at all, or if they are present, they are in lower amounts than we are exposed to on a daily basis through food, water and other natural sources. The one that has attracted the most attention is thiomersal. Thiomersal is a derivative of mercury, and for many years was used in the process of manufacturing vaccines as a preservative. Several vaccines contained traces of thiomersal in the end product. Although this was well below the level that is harmful, it has been removed from all vaccines given to children for the last twenty years. Traces of thiomersal are still present in a few vaccines given to adults, at levels well below those found in nature.
Neurological events following immunizations
Published in Avindra Nath, Joseph R. Berger, Clinical Neurovirology, 2020
Another recent unproven safety concern was raised about the possible link between thimerosal and autism. Thimerosal has been used as a vaccine preservative since the 1930s; it is mercury-based and is metabolized into ethylmercury and thiosalicylate [124–126]. Because of concerns about ill health effects from exposure to environmental mercury, the U.S. Food and Drug Administration (FDA) conducted a risk assessment of the use of thimerosal in vaccines [127]. The assessment suggested that between 1989 and 1998, more thimerosal-containing vaccines were being added to the recommended childhood immunization schedule, leading to increased exposure of children to ethylmercury, and that this exposure could result in received doses of ethylmercury in excess of the U.S. Environmental Protection Agency’s exposure limit for related methylmercury [128]. Although no health effects were detected, out of precaution the U.S. Public Health Service and the American Academy of Pediatrics recommended removal of thimerosal from vaccine formulations [129].
Immunisation in primary care
Published in Ruth Chambers, Kirsty Licence, AI Aynsley-Green, Looking after Children in Primary Care, 2018
Some vaccines include a mercury-containing preservative – thiomersal. This was often added because many vaccines were dispensed in multidose containers and it was important to prevent bacterial contamination. In other vaccines it was part of the manufacturing process. There are no recognised safety limits for the injection of mercury, but there are some for its oral ingestion. However, these vary widely. In 1999, it was noted that if an infant was given all the recommended vaccines in the US programme in the first six months, they would exceed one of these limits. However, the amount would still be below many other thresholds, including those set by WHO and the American Federal Drugs Agency.18 Bearing in mind the precautionary principle and the fact that, in many countries, routine infant vaccines are rarely dispensed in multidose containers, manufacturers were asked to move towards thiomersal-free vaccines. In the UK, even if an infant had been given all the routine vaccines in the previous schedule, the amount of mercury received would not even exceed the lowest of the recommended safety levels. From autumn 2004 none of the routine childhood vaccines contain thiomersal.
Topical preservative-free ophthalmic treatments: an unmet clinical need
Published in Expert Opinion on Drug Delivery, 2021
Michele Figus, Luca Agnifili, Manuela Lanzini, Lorenza Brescia, Francesco Sartini, Leonardo Mastropasqua, Chiara Posarelli
On these bases, the European Medicines Agency (EMA) in 2009 published a statement providing key recommendations for the use of preservatives in ophthalmic preparations in humans [7]. Firstly, pharmaceutical companies should develop preparations without preservatives to cover specific needs of therapy, such as the management of neonatal or pediatric diseases, or chronic eye diseases of the adults, such as DED and glaucoma, or patients intolerant to preserved eyedrops for allergy. Secondly, if preservatives are required, a robust motivation should be given; nevertheless, their concentration should be minimized, maintaining a satisfactory antimicrobial function. Thirdly, pre-clinical and clinical studies are warranted to demonstrate the real advantages of PF formulations in terms of benefit/risk balance. Finally, mercury-containing preservatives, e.g. thiomersal, should be avoided at all [7].
Modern biologics for rabies prophylaxis and the elimination of human cases mediated by dogs
Published in Expert Opinion on Biological Therapy, 2020
Terapong Tantawichien, Charles E. Rupprecht
In general, the CCEEV were intended originally for a single-use application and are not supplied in multidose vials for administration. Also, vaccines prequalified by the WHO do not contain preservatives, such as thiomersal [https://extranet.who.int/gavi/PQ_Web]. Shelf-life is ≥3 years, provided CCEEV are stored at 2–8°C and protected from sunlight. Depending upon the manufacturer, some products have been evaluated for greater thermostability under tropical conditions, but the maintenance of a cold chain remains desirable. After reconstitution with sterile diluent, the vaccines should be used immediately or within ~6 h if kept at 2–8ºC, as partially used vials may become contaminated. These CCEEV are intended for both PrEP and PEP and have been administered to hundreds of millions of people worldwide. Prompt administration after exposure, combined with proper wound management and simultaneous administration of RIG where indicated in naïve individuals, is almost invariably effective in preventing rabies, even after high-risk exposures, such as recipients of RABV-infected tissues and organs [67].
Efficacy, safety, and formulation issues of the combined vaccines
Published in Expert Review of Vaccines, 2020
Physicochemical compatibility of the antigens and other components of the vaccines’ formulation, such as adjuvants, buffers, and preservatives is a crucial factor for development and especially formulation of the combined vaccines [2]. For instance, a trace amount of thimerosal, used as preservative during the early stages of the DTP vaccine manufacturing denatures the polio type 1–3 D-antigens and results in a decrease in the immunogenic potency of the inactivated poliomyelitis vaccine (IPV) in the DTP-based combined vaccines. For this reason, DTP-IPV combined vaccines either must be produced thimerosal-free, filled into the separate injections, or in one injection with separate chambers [103–105]. Incompatibility between Hib antibody response and alum compounds is another example. The reduced antibody quality and, consequently, lower immunogenicity and protection are observed when the alum compounds are used in the DTP-Hib combined vaccines as the adjuvants [106]. Similarly, there could be interactions between the antigens and other components of the combined vaccines’ formulations, such as buffers and stabilizers [2,107,108].