Coronavirus vaccines act like a shield against disease, not an impenetrable barrier, and they offer protection against the omicron variant. Health authorities say booster shots of the Moderna or Pfizer-BioNTech vaccine are the best defense against serious illness, providing robust protection against severe disease. Your likelihood of developing a breakthrough infection is lowest if you’ve gotten the additional shot. The initial two-shot vaccine regimen still offers protection, but it’s not as effective against the omicron variant without boosters.