They found that of more than 1.2 million adults who received at least one dose of either the Pfizer-BioNTech, Oxford-AstraZeneca, or Moderna vaccine, fewer than 0.5 per cent reported a breakthrough infection over 14 days after their first dose.
People most vulnerable to a breakthrough infection after their first vaccine dose included frail older adults, 60 years and older, and those living with underlying conditions such as obesity, heart disease, kidney disease, and lung disease, they said.