COVID vaccine hangover: Symptoms just mean the shot is working, expert says

VANCOUVER – Some Canadians are experiencing more intense reactions after a second dose of a COVID-19 vaccine, and experts say that’s to be expected.

The usual side effects people feel after vaccines, including fever, soreness, and headache, can feel stronger following the second dose. That’s been the case for many people around the world.

Steven Kerfoot, an immunologist with Western University in Ontario, says reactions feeling more intense with your second shot may be because your immune system has already produced antibodies from the first jab.

“Well I don’t think the experiments have been done to absolutely confirm the link here. But I think it’s reasonable to think that that’s why people may be feeling more severe symptoms a second time around, just because there’s this additional antibody detection system in the area that’s ready to respond more quickly and more strongly,” he explained.

But not everyone’s immune systems react the same, and many people have also reported not feeling severe symptoms — and in some cases, say they’ve felt nothing at all.

Kerfoot says that’s OK too.

“People who felt fine after the vaccine or didn’t feel that terrible, I think should still be very confident. For most people, their immune systems have responded just fine, and especially their t-cell responses are just as large. And they still have a good antibody response,” he said.

Related articles: 

• NACI says you can mix-and-match COVID-19 vaccines

• At least 1.3 million Canadians opted to mix COVID-19 vaccines by the end of June

• Flu-like symptoms after COVID jab ‘normal,’ should not deter people from getting vaccinated

It’s been reported mixing and matching vaccines could spark a more intense reaction for some Canadians.

As of the end of June, Health Canada reported at least 1.3 million Canadians opted to mix doses.

A Canadian Press analysis of the data suggests at least half of the mixed-vaccine group in June were people who got the Oxford-AstraZeneca dose first before turning to either Pfizer-BioNTech or Moderna for their second.

In early June, the National Advisory Committee on Immunization (NACI) gave the go-ahead for people to take different vaccines for their first and second doses. NACI noted that a second shot of an mRNA vaccine, Moderna or Pfizer, can be the follow-up to a first dose of AstraZeneca, but that an mRNA shot should be followed by a second dose of an mRNA vaccine.