When someone gets a headache or feels a little under the weather after getting a COVID-19 vaccine, it’s common to hear them say something like “Oh, it just means my immune system is working really hard.” On the other hand, if people don’t notice any side effects, they sometimes worry that the shot isn’t doing its job or that their immune system isn’t responding at all.
Is there a link between what you can notice after a vaccination and what is happening in your body at the cellular level? Here’s What You Should Know.
What Does Your Body Do When You Get a Vaccine?
Your immune system responds to the foreign molecules that make up a vaccine through two different systems.
The initial response is due to what is called the innate immune response. This system is activated as soon as your cells detect that you have been exposed to foreign material, from a splinter to a virus. The goal is to eliminate the intruder. White blood cells called neutrophils and macrophages travel to the invader and work to destroy it.
This first line of defense is relatively short in duration and lasts for hours or days.
The second line of defense takes days to weeks to get going. This is the long-lasting adaptive immune response. It depends on the T and B cells of your immune system learning to recognize certain invaders, such as a coronavirus protein. If the intruder is found again months or even years in the future, it is these immune cells that will recognize the old enemy and generate the antibodies that will knock it out.
In the case of the SARS-CoV-2 vaccines, it takes about two weeks to develop the adaptive response that provides long-term protection against the virus.
When you get the vaccination, what you notice for the first two days is part of your innate immune response: your body’s inflammatory response, aimed at quickly clearing out the foreign molecules that have broken through your body’s outline.
It varies from person to person, but how dramatic the initial reaction is does not necessarily relate to the long-term reaction. In the case of the two mRNA COVID-19 vaccines, more than 90% of the immunized people developed the protective adaptive immune response, while less than 50% experienced side effects, and most were mild.
You may never know how much your body’s adaptive immune response is preparing.
What are possible side effects?
Side effects are normal reactions to the injection of a foreign substance. They include such things as fever, muscle pain, and injection site discomfort, 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 response to occur every time a foreign substance is injected into the body.
In studies where neither the recipients nor the researchers knew which subjects were receiving the mRNA vaccine or a placebo, about half of the people aged 16 to 55 who received a SARS-CoV-2 vaccine developed headaches after the second dose. This reaction may be related to the vaccine, but a quarter of the people who only received a placebo also developed a headache. Thus, in the case of very common symptoms, it can be quite difficult to attribute them to the vaccine with any certainty.
Researchers expect some reports of side effects. Side effects, on the other hand, are things doctors don’t expect as a result of the vaccine. They include organ failure or serious damage to any part of the body.
The blood clots that prompted the US to interrupt distribution of the Johnson & Johnson vaccine are a very rare occurrence, apparently at a frequency of one in a million. Whether they are definitely caused by the vaccine is still under investigation – but if scientists conclude they are, blood clots would be an extremely rare side effect.
Which part of the shot causes side effects?
The only “active ingredient” in the Pfizer and Moderna vaccines are the mRNA instructions that tell the recipient cells to build a viral protein. But the recordings have other components that make the mRNA travel in your body.
In order for the vaccine’s mRNA to get into the cells of the vaccinated person, where it can do its job, it must bypass enzymes in the body that would naturally destroy it. Researchers protected the mRNA in the vaccine by wrapping it in a bubble of lipids to prevent destruction. Other ingredients in the injections – such as polyethylene glycol, which is part of this lipid coat – can cause allergic reactions.
If I feel nauseous after my injection, does that mean strong immunity?
Scientists have found no link between the initial inflammatory response and the long-term response that leads to protection. There is no scientific evidence that anyone with more obvious side effects from the vaccine is better protected against COVID-19. And there’s no reason having an overly innate response would make your adaptive response any better.
Both approved mRNA vaccines provided protective immunity to more than 90% of recipients, but less than 50% reported any response to the vaccine and many fewer had severe reactions.
The bottom line is, you can’t estimate how well the vaccine will work in your body based on what you can detect from the outside. Several people build up stronger or weaker immune responses to a vaccine, but side effects after the injection don’t tell you which one you are. It’s the second, adaptive immune response that helps your body get vaccine immunity, not the inflammatory response that causes those early aches and pains.
This article has been republished from The Conversation under a Creative Commons license. Read the original article.