When the Pfizer’s or Moderna’s COVID shot goes bad
mRNA is fragile and can easily “spoil” in many ways. It could be at the manufacturing plant or on the way to their intended destination.
Despite being encased by lipids, mRNA could deteriorate due to temperature changes.
Spoilage may also occur from a mistake of a worker when preparing single doses from a vial.
Estimates vary as to what percentage of doses are spoiled before even reaching the arms of code recipients.
Related: mRNA vaccine delivery using lipid nanoparticles (2016)