Why some people feel COVID vaccine side effects and others don't Vaxx Populi: Some research has found more side effects after one dose of AstraZeneca than of Pfizer. But there’s no evidence that a stronger reaction means stronger immunity. April 29, 2021 Prime Minister Justin Trudeau receives his COVID vaccination in Ottawa, Friday April 23, 2021. THE CANADIAN PRESS/Adrian Wyld On April 23, Prime Minister Justin Trudeau and his wife, Sophie, got their AstraZeneca COVID-19 vaccine shots at a pharmacy in Ottawa. Four days later, the PM reported, “We’re feeling great.” But some people are feeling downright rotten after getting a shot. My colleague Shannon Proudfoot spoke for many when she noted, “Just to offer encouragement to anyone else experiencing the AstraZeneca hangover, I felt like absolute garbage—fever, chills, headache, muscle aches—until about 27 hours after my shot, then things improved rapidly. So it’s brutal but brief, courage!”