Sore arm, fatigue, muscle pain and fever are some of the side effects reported in people who received the COVID-19 vaccines, and experts say this is a good thing.
Vaccines must trigger an immune response, they say. That’s how you know they are working.
“If you have a vaccine that does not produce a reaction in people, the resulting immune response is weaker,” said Earl Brown, a microbiologist at the University of Ottawa.
Brown says the vaccines work by stimulating immune cells to grow and communicate with each other, giving instructions on where to prepare for an impending virus attack. This results in inflammation, with some of these cells traveling to the lymph nodes and causing swelling.
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Pfizer-BioNTech and Moderna mRNA vaccines provide immune cells with instructions for making the spike protein COVID and making antibodies. Viral vector vaccines like Oxford-AstraZeneca and Johnson & Johnson, meanwhile, force an immune response from the harmless version of the virus that is injected with the jabs.
“Vaccines make your immune cells start to recruit more companions, saying ‘we’re giving you a new answer. We need all of you here, ”said Brown. “So the inflammation is good. This makes the immune system stronger. “
The World Health Organization says that the side effects of COVID vaccines have been mainly “mild to moderate and short-lived” 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 specialist at the University of Alberta, says that cases of adverse effects are on the rise because many people are being vaccinated now. The percentage of those who develop these mild to moderate side effects is still quite low compared to the number of people being immunized.
She notes that while more serious effects are possible – a small number have had severe 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 or more of the participants – after the second dose. It was unusual after the first dose of Moderna, but very common after the second.
Brown says the effects are generally more apparent after the second doses, because the body has developed a stronger immune response since the initial injection.
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Although Saxinger says that fever is a “strong reaction” to a vaccine, it should not last more than a few days. She also says that it is not advisable to take anti-inflammatory drugs before a vaccine to lessen the possible effects, since you want to elicit this immune response.
“It appears that mRNA vaccines are particularly talented at simulating infection,” she added. “This strong, very targeted immune response is what we ultimately want.”
Health Canada data shows that 0.085 percent of doses administered in the country from mid-December to March 5th resulted in an adverse reaction, with 0.009 percent being considered serious. Pain, redness and swelling at the vaccination site were the most common effects.
Most of these doses would have been mRNA vaccines, which generally elicit stronger reactions than viral vector jabs.
Saxinger says this may be related to the initial effectiveness of vaccines. While Pfizer and Moderna offer higher levels of effectiveness immediately, AstraZeneca and Johnson & Johnson increase over time.
“It is more of a slow and steady profile compared to the rapid response pattern of mRNA,” she said. “So there is a parallel to the strength of the initial immune reaction.”
But why do some people experience side effects and others don’t?
Brown says that age is perhaps the biggest determining factor, noting that older people, who tend to have less robust immune systems, report fewer reactions. Canada’s vaccine supply to date has been administered primarily to older populations.
The absence of side effects does not mean that the vaccine is not working, Brown added. Some people simply do not show external reactions.
News from Europe last week caused concern about the AstraZeneca product after some adverse events, including blood clots, were reported after vaccination. This has prompted nearly a dozen countries to pause using the product while experts investigate a possible link.
Canadian health officials said they were keeping an eye on European investigations, but added that there was no evidence that the clots were caused by the vaccine.
AstraZeneca issued a statement on Sunday saying that an analysis of 17 million patients who received the injection 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 pulmonary embolism, deep vein thrombosis or thrombocytopenia in any age group, sex, vaccine batch 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 less than what would naturally occur in a population of more than 17 million people.
Blood clots are quite common, says Saxinger, so researchers will look at the overall number of people who received the AstraZeneca vaccine compared to those who reported the disease.
“There are so many people who get vaccines daily that any health event that happens to someone at the time they get the vaccine may or may not be related,” said Saxinger.
Brown says news of possible side effects should not deter people from being vaccinated.
“See this as manageable, short-term discomfort without harm, compared to a real illness that can alter or end life.”
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© 2021 The Canadian Press