Fun fact: Up to the Civil War or WWI, more soldiers died of illness than of battle wounds. So much for the fabled immune system. And if WWI killed more soldiers in battle, the flu still won that round, because the Spanish Flu killed heaps more later. Now we still remember WWI for its bloodiness, but without Covid-19, who would remember the Spanish Flu?

  Lipid nanoparticle mRNA vaccines have revolutionized vaccinology and saved many lives during the COVID-19 pandemic.1 Lipid nanoparticle mRNA vaccines typically contain 5 materials – mRNA, an ionizable lipid, a polyethylene glycol (PEG)–lipid, a helper lipid and cholesterol. Although the vaccines are delivered intramuscularly (IM) and act primarily in the draining lymph node, recent studies have suggested that at least small amounts of the mRNA vaccines may distribute in humans more widely than originally anticipated. A primarily cross-sectional study detected mRNA in blood for up to 15 days after mRNA vaccination.2 Low levels of the vaccine mRNA were detected in breast milk up to 45 hours post-vaccination.3,4 An autopsy study of people dying incidentally after vaccination found mRNA in tissues (axillary lymph nodes and heart) up to 30 days after vaccination.5 Presumably the mRNA reached breast milk and tissues following circulation in blood. Despite evidence in animals and humans that mRNA can be detected in blood after vaccination,2,6 studies of the pharmacokinetics of mRNA lipid nanoparticle components in blood in humans are lacking.