If someone gets a headache or feels a bit under the weather after receiving a COVID-19 vaccine, it’s become common to hear them say something like Oh, it just means my immune system is really working hard. On the flip side, when people don’t notice any side effects, they sometimes worry the shot isn’t doing its job or their immune system isn’t reacting at all.
WHAT DOES YOUR BODY DO WHEN YOU GET A VACCINE?
Your immune system responds to the foreign molecules that make up any vaccine via two different systems.
The initial response is due to whats called the innate immune response. This system is activated as soon as your cells notice you’ve been exposed to any foreign material, from a splinter to a virus. Its goal is to eliminate the invader. White blood cells called neutrophils and macrophages travel to the intruder and work to destroy it.
This first line of defense is relatively short-lived, lasting hours or days.
The second line of defense takes days to weeks to get up and running. This is the long-lasting adaptive immune response. It relies on your immune systems T and B cells that learn to recognize particular invaders, such as a protein from the coronavirus. If the invader is encountered again, months or even years in the future, it’s these immune cells that will recognize the old enemy and start generating the antibodies that will take it down.
When you get the vaccine shot, what you are noticing in the first day or two is part of the innate immune response: your bodys inflammatory reaction, aimed at quickly clearing the foreign molecules that breached your bodys perimeter.
It varies from person to person, but how dramatic the initial response is does not necessarily relate to the long-term response. In the case of the two mRNA COVID-19 vaccines, well over 90% of people immunized developed the protective adaptive immune response while fewer than 50% developed any side effects, and most were mild.
You may never know how strongly your bodys adaptive immune response is gearing up.
WHAT ARE SIDE EFFECTS, ANYWAY?
Side effects are normal responses to the injection of a foreign substance. They include things like fever, muscle pain and discomfort at the injection site, and are mediated by the innate immune response.
Neutrophils or macrophages in your body notice the vaccine molecules and produce cytokines molecular signals that cause fever, chills, fatigue and muscle pain. Doctors expect this cytokine reaction to happen any time a foreign substance is injected into the body.
In studies where neither recipients nor researchers knew which individuals were getting the mRNA vaccine or a placebo, approximately half of people aged 16 to 55 who received a SARS-CoV-2 vaccine developed a headache after the second dose. This reaction may relate to the vaccine but a quarter of people who received just a placebo also developed a headache. So in the case of very common symptoms, it can be quite difficult to attribute them to the vaccine with any certainty.
Researchers anticipate some reports of side effects. Adverse events, on the other hand, are things that physicians do not expect to happen as a result of the vaccine. They would include organ failure or serious damage to any part of the body.
WHAT COMPONENT IN THE SHOT CAUSES SIDE EFFECTS?
The only active ingredient in the Pfizer and Moderna vaccines is the mRNA instructions that tell the recipients cells to build a viral protein. But the shots have other components that help the mRNA travel inside your body.
To get the vaccines mRNA into the vaccinated person cells where it can do its job, it must evade enzymes in the body that would naturally destroy it. Researchers protected the mRNA in the vaccine by wrapping it in a bubble of lipids that help it avoid destruction. Other ingredients in the shots like polyethylene glycol, which is part of this lipid envelope could cause allergic responses.
IF I FEEL SICK AFTER MY SHOT, DOES THAT SIGNAL STRONG IMMUNITY?
Scientists haven’t identified any relationship between the initial inflammatory reaction and the long-term response that leads to protection. Theres no scientific proof that someone with more obvious side effects from the vaccine is then better protected from COVID-19. And theres no reason that having an exaggerated innate response would make your adaptive response any better.
Both the authorized mRNA vaccines provided protective immunity to over 90% of recipients, but fewer than 50% reported any reaction to the vaccine and far fewer had severe reactions.
By Robert Finberg, a professor of medicine at the University of Massachusetts Medical School
This article is republished from The Conversation under a Creative Commons license. Read the original article.
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