Sore arms, fatigue, muscle aches, and fever are some of the side effects reported in those receiving COVID-19 vaccines, and experts say this is especially good.
Vaccines are said to elicit an immune response. This is how they are known to be working.
“If you have a vaccine that produces no reaction in people, 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, giving indications to establish an impending attack by the virus. This causes inflammation, with some of these cells traveling to the lymph nodes and causing swelling.
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Pfizer-BioNTech and Moderna mRNA vaccines instruct immune cells to make the COVID spike protein and produce antibodies. Meanwhile, viral virus vaccines, such as Oxford-AstraZeneca and Johnson & Johnson, require an immune response from the harmless version of the virus that is injected with these stings.
“Vaccines get immune cells to start recruiting more of their friends, saying‘ we are giving a new answer. We need everyone here, “Brown said.” So the inflammation is good. It makes the immune system stronger. “
The World Health Organization says the side effects of COVID vaccines have been mostly “mild to moderate and short-lived” and include: fever, fatigue, headache, muscle aches, chills, diarrhea, and injection site.
But how often do they happen?
Dr. Lynora Saxinger, an infectious disease expert at the University of Alberta, says cases of side effects are on the rise because so many people are now getting vaccinated. The percentage of people who develop these mild to moderate side effects is still quite low compared to the number of people immunized.
She points out that while more serious effects are possible (a small number have experienced severe allergic reactions), these events are rare.
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Fever was common after the first dose of Pfizer and was “very common,” defined as present in 10% or more of participants, after the second dose. It was uncommon after the first dose of Moderna, but very uncommon after the second.
Brown says the effects are usually more evident after second doses because the body has accumulated a stronger immune response from the initial puncture.
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Although Saxinger says fever is a “strong reaction” to a vaccine, it shouldn’t last more than a few days. He also says it is not recommended to take anti-inflammatory drugs before a vaccine to lessen the possible effects, as this immune response is intended to be illicit.
“It seems that mRNA vaccines are especially talented at mimicking infection,” he added. “This very targeted and strong immune response is what we finally want.”
Health Canada data show that 0.085% of doses administered in the country from mid-December to March 5 caused an adverse reaction, with 0.009% considered severe. Pain, redness, and inflammation at the site of vaccination were the most common effects.
Most of these doses would have been mRNA vaccines, which generally cause stronger reactions than viral vector spikes.
Saxinger says this could be related to the initial effectiveness of the vaccines. While Pfizer and Moderna offer higher levels of efficiency immediately, AstraZeneca and Johnson & Johnson are accumulating over time.
“It’s more of a slow, steady profile versus the fast press, a fast mRNA response,” he said.
But why do some people experience side effects while others do not?
Brown says age is perhaps the most important determinant, noting that older people, who tend to have a less robust immune system, report fewer reactions. To date, Canada’s vaccine supply has been administered primarily to larger populations.
The absence of side effects does not mean the vaccine will not work, Brown added. Some people will simply not show external reactions.
Last week, news outside Europe caused concern about the AstraZeneca product following the notification of some adverse events, including blood clots, following the vaccination. This encouraged nearly a dozen countries to stop using the product while experts investigated a possible link.
Canadian health authorities said they were monitoring European investigations, but added that there was no evidence that the clots were caused by the vaccine.
AstraZeneca released a statement on Sunday saying that a review of 17 million patients who received the vaccine in Europe and the UK showed no high risk of blood clotting.
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Ann Taylor, the company’s medical director, said there is no increased risk of either pulmonary embolism, deep vein thrombosis or thrombocytopenia in any age group, gender, vaccine batch 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 would occur naturally in a population of more than 17 million people.
Blood clots are quite common, Saxinger says, so researchers will examine the overall number of people who received the AstraZeneca vaccine compared to those who reported the disease.
“There are so many people who get vaccinated on a daily basis that any health event that happens to anyone at the time of receiving the shot may or may not be related,” Saxinger said.
Brown says news of possible side effects should not deter people from getting vaccinated.
“Look at it as a short-term, manageable nuisance without damage, compared to a real illness that can alter life or end life.”
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