The success of these COVID-19 vaccines is remarkable and was far from guaranteed. mRNA is incredibly delicate. Enzymes in the environment and in our bodies are quick to chop mRNA into pieces, making lab experiments difficult and the delivery of mRNA to our cells daunting. On top of that, mRNA strands are large and negatively charged and can’t simply waltz across the protective lipid membranes of cells. Many scientists thought the technology would never work.