Your second COVID-19 shot might cause more side effects than the first â don't panic Health leaders said it only happens for about 20% of patients and itâs not a reason to avoid getting vaccinated, but itâs important to know what to expect when you get the shot. and last updated 2021-01-15 18:43:23-05 The side effects from the second dose of the COVID-19 vaccine might pack more of a punch than the first one, local health leaders confirmed Friday. It only happens for about 20% of patients, they said, and itâs not a reason to avoid getting vaccinated, but itâs important to know what to expect when you get the shot.