Many struggle with 2nd dose

Becca Young woke up the day after getting her second dose of a COVID-19 vaccine with a body so sore and head so achy it felt as if she’d been dancing and drinking at a raging party the night before.

Young, a trivia host from Kitchener, Ont., and her husband Matt Neil received their second mRNA vaccine on Saturday. But while Neil felt fine aside from a minor headache, Young could barely get out of bed for most of Sunday.

“Sore arm, sore back, just super achy. And my head – it was kind of reminiscent of an alcohol hangover,” she said with a laugh. “It’s funny because the first vaccine I got was Pfizer and the second was Moderna. So I did get a cocktail.”

Young, who had only a sore arm after her first dose, is among many Canadians to experience stronger reactions to the second jab, and experts say that’s normal.

Nafissa Ismail, director of the Neuro Immunology, Stress and Endocrinology (NISE) Laboratory at the University of Ottawa, said while the immune system generally responds less severely when reexposed to a pathogen a second time, that’s not how our COVID-19 vaccines work.

Instead, mRNA and viral-vector vaccines give cells instructions on how to detect the coronavirus’s spike protein so that the body can mount a defence if it meets the actual virus.

“They are not injecting us with a weakened form of the virus or a dead form of the virus,” Ismail said, referring to common methods of other vaccines. “So the first time we get the message, our immune system hasn’t yet produced antibodies.

“But when we get the second dose ... there’s this dual action where some antibodies are already there and ready to fight, plus we’re asking the immune system to make more antibodies. So symptoms tend to get amplified.”

Everyone’s immune system responds differently to vaccines, which Ismail said is the reason so many varying side effects are reported. Soreness, headache, fatigue and fever symptoms tend to last only a day or two, but can linger for some people.

Younger adults, who typically have robust immune systems, are more likely to experience routine reactions, Ismail added, while women also generally have stronger responses for the same reason.

Health Canada’s report on COVID-19 vaccine side effects, which includes reactions disclosed by people following first or second doses, shows 79.1 per cent of adverse events are reported by women – a rate of 38.6 reports per 100,000 doses administered, compared to 11.6 from men.