A dose of the Pfizer-BioNTech COVID-19 vaccine is given to a recipient at a vaccination site in Vancouver Thursday, March 11, 2021. THE CANADIAN PRESS/Jonathan Hayward

A dose of the Pfizer-BioNTech COVID-19 vaccine is given to a recipient at a vaccination site in Vancouver Thursday, March 11, 2021. THE CANADIAN PRESS/Jonathan Hayward

Fatigue, soreness, fever: experts say some side effects mean vaccines are working

Data from Health Canada shows 0.085 per cent of doses resulted in an adverse reaction

Sore arm, fatigue, muscle pain and fever are some of the side effects being reported in those receiving COVID-19 vaccines, and experts say that’s mostly a good thing.

Vaccines are supposed to trigger an immune response, they say. That’s how you know they’re working.

“If you have a vaccine that doesn’t produce a reaction in people, the resulting immune response is weaker,” said Earl Brown, a microbiologist with the University of Ottawa.

Brown says vaccines work by stimulating our immune cells to grow and communicate with each other, giving directions on where to set up for an impending attack by the virus. That results in inflammation, with some of those cells traveling to lymph nodes and causing swelling.

The mRNA vaccines from Pfizer-BioNTech and Moderna give immune cells instructions to make the COVID spike protein and produce antibodies. Viral vector vaccines like Oxford-AstraZeneca and Johnson & Johnson, meanwhile, force an immune response from the harmless version of the virus that’s injected with those jabs.

“The vaccines get your immune cells to start recruiting more of their buddies, saying ‘we’re making a new response. We need all you guys here,’” Brown said. “So the inflammation is good. It makes the immune system stronger.”

The World Health Organization says side effects to COVID vaccines have been mostly “mild to moderate and short-lasting” and include: fever, fatigue, headache, muscle pain, chills, diarrhea and pain at the injection site.

But how often do they happen?

Dr. Lynora Saxinger, an infectious disease expert with the University of Alberta, says cases of adverse effects are increasing because so many people are getting vaccinated now. The percentage of those that develop these mild to moderate side effects is still quite low compared to the number of people being immunized.

She notes that while more severe effects are possible — a small number have experienced serious allergic reactions — those events are rare.

Fever was common after the first dose of Pfizer and “very common” — defined as present in 10 per cent of participants or more — after the second dose. It was uncommon after the first dose of Moderna but very common after the second.

Brown says effects are generally more apparent following second doses because the body has built up a stronger immune response from the initial jab.

While Saxinger says a fever is a “strong reaction” to a vaccine, it shouldn’t last more than a few days. She also says taking anti-inflammatories before a vaccine to lessen possible effects isn’t advised, since you want to illicit that immune response.

“It looks like mRNA vaccines are particularly talented at mimicking infection,” she added. “That very targeted and strong immune response is what we ultimately want.”

READ MORE: Why is there no COVID vaccine for kids yet? A B.C. researcher breaks it down

Data from Health Canada shows 0.085 per cent of doses administered in the country from mid-December to March 5 resulted in an adverse reaction, with 0.009 per cent considered serious. Pain, redness and swelling at the vaccination site were the most common effects.

Most of those doses would have been mRNA vaccines, which are generally eliciting stronger reactions than the viral vector jabs.

Saxinger says that could be related to the initial efficacy of the vaccines. Whereas Pfizer and Moderna offer higher levels of effectiveness right away, AstraZeneca and Johnson & Johnson build up over time.

“It’s more of a slow-and-steady profile versus the hot-off-the-presses, quick response from the mRNA,” she said “So there’s a parallel there with the vigorousness of the initial immune reaction.”

But why do some people experience side effects while others don’t?

Brown says age is perhaps the biggest determining factor, noting older people, who tend to have less robust immune systems, report fewer reactions. Canada’s vaccine supply to date has mostly been administered to older populations.

The absence of side effects doesn’t mean the vaccine isn’t working, Brown added. Some people simply won’t show outward reactions.

News out of Europe last week caused concern over AstraZeneca’s product after some adverse events, including blood clots, were reported following vaccination. That spurred nearly a dozen countries to pause their use of the product while experts investigate a possible link.

Canadian health authorities said they were keeping a watchful eye on the Europeans investigations, but added there is no evidence the clots were caused by the vaccine.

AstraZeneca released a statement on Sunday saying a review of 17 million patients who received the shot in Europe and the U.K. showed no elevated risk of blood clotting.

Ann Taylor, the company’s chief medical officer, said there’s no increased risk of either pulmonary embolism, deep vein thrombosis or thrombocytopenia in any age group, gender, batch of vaccines or country.

The company said there are reports of 15 patients experiencing deep-vein thrombosis and 22 pulmonary embolisms as of March 8, which is much lower than what would occur naturally in a population of more than 17 million people.

Blood clots are fairly common, Saxinger says, so investigators will look at overall numbers of people who received the AstraZeneca vaccine compared to those who reported the condition.

“There’s so many people receiving vaccines daily that any health event that happens to anyone around the time they get their shot may or may not be related,” Saxinger said.

Brown says news of possible side effects shouldn’t dissuade people from getting vaccinated.

“Look at it as short-term, manageable discomfort without damage, compared to a real disease that could be life-altering or life-ending.”

The Canadian Press


Like us on Facebook and follow us on Twitter.

Want to support local journalism during the pandemic? Make a donation here.

Coronavirusvaccines

Get local stories you won't find anywhere else right to your inbox.
Sign up here

Just Posted

This photo shows crews the fire at 7987 Galbraith Cres. that caused extensive damage and displaced six residents early Sunday morning. (Central Saanich Fire/Department Twitter)
Central Saanich rallies around couple who lost home of 25 years

A GoFundMe campaign is currently underway for Carla and Brian Wallace

The government map (as of April 22) showing vaccine availability doesn’t have any Saanich Peninsula pharmacies listed, but the situation is fluid, and many readers have already registered. (Province of B.C. screenshot)
Vaccine availability a fluid situation for Saanich Peninsula

Government site may not show pharmacies, but registering still an option

Volunteers with the Esquimalt Farmers Market will be on hand at Bullen Field to direct attendees and clarify public health protocols. The market runs Thursdays now through Sept. 16, from 4:30-7:30 p.m. (Facebook/Esquimalt Farmers Market)
Esquimalt Farmers Market continues tonight at Bullen Field

Award-winning market features farm-fresh products, food trucks, COVID-19 protocols for safety

A member of the Belmont Secondary School in Langford has tested positive for COVID-19, the Sooke School District announced Thursday afternoon. (Black Press Media File Photo)
Positive COVID-19 case identified at Belmont Secondary School in Langford

Other school members could’ve been exposed on April 20

While Buccaneer Days public events are cancelled again, such as the annual parade, a home and business decorating contest will allow the spirit of the event to live on. (Facebook)
Esquimalt Buccaneer Days COVID-19 cannon fodder again

Annual celebration cancelled a second time, decorating contest full steam ahead

Canadian Prime Minister Justin Trudeau and United States President Joe Biden smile as they say farewell following a virtual joint statement in Ottawa, Tuesday, February 23, 2021. THE CANADIAN PRESS/Adrian Wyld
Trudeau pledges to cut emissions by 40% to 45% by 2030, short of U.S. goal

Trudeau announced target during a virtual climate summit convened by U.S. President Joe Biden

(Black Press Media file photo)
POLL: Have rising prices caused you to give up hope of buying a home?

Do you have a spare 50 grand or so kicking around (have… Continue reading

Anyone with information on any of these individuals is asked to call 1-800-222-TIPS (8477) or visit the website victoriacrimestoppers.ca for more information.
Greater Victoria Crime Stoppers wanted list for the week of April 20

Greater Victoria Crime Stoppers is seeking the public’s help in locating the… Continue reading

MLA Shirley Bond, right, answers questions during a press conference at Legislature in Victoria, B.C., on February 19, 2019. THE CANADIAN PRESS/Chad Hipolito
Former B.C. gaming minister says she wasn’t told directly about dirty cash flowing to casinos

Shirley Bond said Thursday civil forfeiture, gang violence and gambling addiction were also major concerns in 2011

RCMP Constable Etsell speaks to tourists leaving the area at a police roadblock on Westside Road south of Fintry, B.C., Thursday, July 23, 2009. THE CANADIAN PRESS/ Yvonne Berg
B.C. police say they take ‘exception’ to conducting roadblocks limiting travel

Asking the police to enforce roadblocks exposes officers to further risk and possible COVID-19 infections, says federation president Brian Sauve

The conservation service confirmed they do not relocate cougars from settled areas but that euthanasia is not necessarily the fate for an animal in the Fanny Bay area. The hope is that the animal will move on to wild areas. (File photo)
Woman hopes cat-stalking Fanny Bay cougar can avoid euthanization

Conservation officers do not relocate the animals from Vancouver Island

Tofino residents expressed frustration over a recent post by Long Beach Lodge owner Tim Hackett that falsely claimed all residents have been vaccinated. (Westerly file photo)
Resort owner apologizes for suggesting Tofino is safe to travel to

Long Beach Lodge owner Tim Hackett apologizes to community and visitors

BC Hydro released a survey Thursday, April 22. It found that many British Columbians are unintentionally contributing to climate change with their yard maintenance choices. (Pixabay)
Spend a lot of time doing yard work? It might be contributing to climate change

Recent BC Hydro survey finds 60% of homeowners still use gas-powered lawnmowers and yard equipment

Journal de Montreal is seen in Montreal, on Thursday, April 22, 2021. The daily newspaper uses a file picture of Prime Minister Justin Trudeau dressed in traditional Indian clothing during his trip to India to illustrate a story on the Indian variant of the coronavirus. Paul Chiasson/The Canadian Press
Montreal newspaper blasted for front-page photo of Trudeau in India

Trudeau is wearing traditional Indian clothes and holding his hands together in prayer beside a caption that reads, ‘The Indian variant has arrived’

Most Read