There’s been a great concern about the new Omicron variant of SARS-CoV-2, the coronavirus that causes COVID-19. A major reason is Omicron has accumulated over 50 mutations, including about 30 in the spike protein, the part of the coronavirus that mRNA vaccines teach our immune systems to attack. All of these genetic changes raise the possibility that Omicron could cause breakthrough infections in people who’ve already received a Pfizer or Moderna mRNA vaccine.