Arm pain, fatigue, muscle aches and fever are some of the side effects reported in those who receive COVID-19 vaccines, and experts say this is usually a good thing.
Vaccines should elicit an immune response, they say. That’s how you know they work.
“If you have a vaccine that doesn’t cause a response in humans, the resulting immune response is weaker,” said Earl Brown, a microbiologist at the University of Ottawa.
Brown says vaccines work by stimulating our immune cells to grow and communicate with each other, providing clues as to where to prepare for an upcoming attack by the virus. That results in inflammation, in which some of those cells travel to the lymph nodes and cause swelling.
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The mRNA vaccines from Pfizer-BioNTech and Moderna instruct immune cells to make the COVID spike protein and produce antibodies. Viral vector vaccines such as Oxford-AstraZeneca and Johnson & Johnson, meanwhile, force an immune response from the harmless version of the virus injected with those shots.
“The vaccines make your immune cells recruit more of their friends by saying ‘we come up with a new response’. We need you all here, ” said Brown. So the ignition is good. It makes the immune system stronger. “
The World Health Organization says the side effects of COVID vaccines were usually “mild to moderate and short-lived” and included: fever, fatigue, headache, muscle aches, chills, diarrhea, and pain at the injection site.
But how often do they occur?
Dr. Lynora Saxinger, an infectious disease expert at the University of Alberta, says the number of side effects is increasing because so many people are now being vaccinated. The percentage of those who develop these mild to moderate side effects is still quite low compared to the number of people who are immunized.
She notes that while more serious effects are possible – a small number have experienced serious allergic reactions – these events are rare.
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Fever was common after the first dose of Pfizer and “very common” – defined as present in 10 percent of the participants or more – after the second dose. It was unusual after the first dose of Moderna, but very common after the second dose.
Brown says the effects are generally more evident after second doses because the body has built a stronger immune response from the first shot.
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Although Saxinger says a fever is a “strong reaction” to a vaccine, it shouldn’t last more than a few days. She also says that taking anti-inflammatories before a vaccine to reduce potential effects is not recommended because you want to debunk that immune response.
“It appears that mRNA vaccines are particularly talented at mimicking infections,” she added. “That highly targeted and strong immune response is what we ultimately want.”
Data from Health Canada shows that 0.085 percent of doses administered in the country from mid-December to March 5 resulted in an adverse reaction, with 0.009 percent 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 generally elicit stronger responses than the viral vector shots.
Saxinger says this may be related to the initial efficacy of the vaccines. While Pfizer and Moderna offer higher effectiveness right away, AstraZeneca and Johnson & Johnson build over time.
“It’s more of a slow and stable profile compared to the hot-off-the-presses, fast mRNA response,” she said. “So there is a parallel with the strength of the initial immune response.”
But why do some people experience side effects and others not?
Brown says age is perhaps the biggest determining factor, noting that older people, who tend to have less robust immune systems, report fewer responses. Canada’s vaccine supply to date has mainly been administered to older populations.
The absence of side effects doesn’t mean the vaccine isn’t working, Brown added. Some people just won’t show any outward reactions.
News from Europe last week raised concerns about AstraZeneca’s product after some side effects, including blood clots, were reported after vaccination. That spurred nearly a dozen countries to discontinue use of the product while experts investigate a possible link.
Canadian health authorities said they were closely monitoring European investigations, but added that there is no evidence that the blood clots were caused by the vaccine.
AstraZeneca released a statement on Sunday saying that a review of 17 million patients who received the injection in Europe and the UK did not show an increased risk of blood clotting.
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Ann Taylor, the company’s chief medical officer, said there is no increased risk of pulmonary embolism, deep vein thrombosis, or thrombocytopenia in any age group, gender, batch of vaccines, or country.
The company said there were reports of 15 patients with deep vein thrombosis and 22 pulmonary embolisms on March 8, which is much lower than what would naturally occur in a population of more than 17 million people.
Blood clots are quite common, Saxinger says, so researchers will look at the total number of people who received the AstraZeneca vaccine compared to those who reported the condition.
“There are so many people who receive vaccines every day that every health event that happens to someone around the time they get their shot may or may not be related,” Saxinger said.
Brown says news of potential side effects shouldn’t stop people from getting vaccinated.
“Think of it as manageable short-term discomfort with no harm, compared to a real illness that can be life-altering or life-ending.”
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© 2021 The Canadian Press