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

Rainbow trouts thrashing with life as they’re about to be transferred to the largest lake of their lives, even though it’s pretty small. These rainbows have a blue tinge because they matched the blue of their hatchery pen, but soon they’ll take on the green-browns of their new home at Lookout Lake. (Zoe Ducklow/News Staff)
VIDEO: Lookout Lake stocked with hatchery trout to delight of a seniors fishing club

The Cherish Trout Scouts made plans to come back fishing soon

Traffic is backed up due to a crash on Highway 1. (Photo courtesy of Google Maps)
Traffic backs up on Highway 1 westbound in View Royal after crash

First responders are reportedly on the scene in View Royal

A driver stopped by Saanich police following a road rage incident on April 15 was found to be impaired, in violation of a license restriction and in a damaged vehicle. They received a 90-day driving prohibition and a 30-day vehicle impound. (Saanich Police Traffic Safety Unit/Twitter)
Driver stopped on Pat Bay Highway after road rage reports fails breathalyzer test: police

Several witnesses reported driver to Saanich police, school officer intercepted

Pacific Institution in Abbotsford. (Black Press Media file photo)
Inmate with ties to Victoria dies in Abbotsford institution

Brodie Bingley, who was sentenced for aggravated assault in Maple Ridge died April 13

The site of the proposed rental housing development at 2197 Otter Point Rd. (District of Sooke)
District of Sooke approves development with 77 rental units

New parking lot for John Phillips Memorial Park included in project

A woman wears a protective face covering to help prevent the spread of COVID-19 as she walks past the emergency entrance of Vancouver General Hospital in Vancouver, B.C., Friday, April 9, 2021. COVID-19 cases have been on a steady increase in the province of British Columbia over the past week. THE CANADIAN PRESS/Jonathan Hayward
Top doctor warns B.C.’s daily cases could reach 3,000 as COVID hospitalizations surge

There are more than 400 people in hospital, with 125 of them in ICU

(Black Press Media file photo)
POLL: Do you have a plan in place in the event of a tsunami?

Tsunamis have claimed the lives of more than 250,000 people between 1998… 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 13

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

A crossing guard stops traffic as students wearing face masks to curb the spread of COVID-19 arrive at Ecole Woodward Hill Elementary School, in Surrey, B.C., on Tuesday, February 23, 2021. A number of schools in the Fraser Health region, including Woodward Hill, have reported cases of the B.1.7.7 COVID-19 variant first detected in the U.K. THE CANADIAN PRESS/Darryl Dyck
COVID-infected students in Lower Mainland schools transmitting to 1 to 2 others: data

Eight to 13 per cent of COVID cases among students in the Lower Mainland were acquired in schools, B.C. says

An armed officer walks outside Cerwydden Care on Cowichan Lake Road near Skinner Road Wednesday, April 14 around 5:30 p.m. (Kevin Rothbauer/Citizen)
Police standoff at Duncan apartment ends peacefully

Officers surround building as homeowner held in apartment for nearly four hours by adult son

Latest modelling by public health shows cases generated by COVID-19 infections into places where it can spread quickly. (B.C. Centre for Disease Control)
Industrial sites, pubs, restaurants driving COVID-19 spread in B.C.

Infection risk higher in offices, retail, warehouses, farms

The District of Sooke will continue to flower with Communities in Bloom. (Pixabay)
Sooke will bud but not bloom in provincial competition

Council scales back participation in Communities in Bloom

The father of Aaliyah Rosa planted a tree and laid a plaque in her memory in 2018. (Langley Advance Times files)
Final witness will extend Langley child murder trial into May or June

Lengthy trial began last autumn with COVID and other factors forcing it to take longer than expected

Most Read