Photo credit: Diagram: The Conversation, CC-BY-ND Source: Gee J., Marquez P., Su J., et al. First Month of COVID-19 Vaccine Safety Monitoring – US, December 14, 2020 – January 13, 2021. MMWR Morb Mortal Wkly Rep 2021; 70: 283-288
When someone gets a headache or feels a little under the weather after receiving a COVID-19 vaccine, they are often heard saying, “Oh, that just means my immune system is working really hard.” On the flip side, when people aren’t experiencing any side effects, they sometimes worry that the shot isn’t doing its job or that their immune systems aren’t responding at all.
Is there a link between what you may see after a vaccination and what is happening in your body at the cellular level? Robert Finberg is an infectious disease and immunology doctor at the University of Massachusetts Medical School. He explains that this perception is inconsistent with the reality of how vaccines work.
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 reaction is due to what is known as the innate immune response. This system is activated as soon as your cells discover that they have been exposed to foreign material, from splinters to viruses. Your goal is to eliminate the intruder. White blood cells called neutrophils and macrophages migrate to the invader and work to destroy it.
This first line of defense is relatively short-lived and lasts for hours or days.
The second line of defense takes days to weeks to get operational. This is the long lasting adaptive immune response. It is based on your immune system’s T and B cells, which learn to recognize certain invaders, such as a protein from the coronavirus. When the intruder is encountered again months or even years later, these immune cells recognize the old enemy and create the antibodies that turn them off.
With the SARS-CoV-2 vaccines, it takes about two weeks to develop the adaptive response that provides permanent protection against the virus.
When you receive the vaccine, what you notice on the first or second day is part of the innate immune response: your body’s inflammatory response, which aims to quickly get rid of the foreign molecules that break through the girth of your body.
It varies from person to person, but how dramatic the initial response is isn’t necessarily related to the long-term response. For the two mRNA COVID-19 vaccines, well over 90% of those immunized developed the protective adaptive immune response, while less than 50% developed side effects and most were mild.
You may never know how much your body’s adaptive immune response is speeding up.
The bottom line is that you can’t judge how well the vaccine is working inside your body based on what you can tell from the outside. Different people will be more or less responsive to a vaccine, but the side effects after the shot won’t tell you who you are. It is the second adaptive immune response that helps your body gain immunity to vaccines, not the inflammatory response that causes this early pain.
What are side effects anyway?
Side effects are normal reactions to the injection of a foreign substance. These include 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 occur every time a foreign substance is injected into the body.
In studies where neither recipients nor researchers knew which people were receiving the mRNA vaccine or a placebo, about half of 16- to 55-year-olds 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 people who received only a placebo also got a headache. If symptoms are very common, it can therefore be difficult to assign them to the vaccine with certainty.
The researchers await some reports of side effects. Adverse events, on the other hand, are things doctors don’t expect because of the vaccine. These include organ failure or severe damage to parts of the body.
The blood clots that caused the US to cut off the distribution of the Johnson & Johnson vaccine is a very rare occurrence that appears to occur with a frequency of one million. Whether they are definitely caused by the vaccine is still being investigated – but if scientists conclude that it is, blood clots would be an extremely rare side effect.
Which component in the intake causes side effects?
The only “active ingredient” in the Pfizer and Moderna vaccines are the mRNA instructions, which tell the recipient’s cells to make a viral protein. But the recordings have other components that help the mRNA move around your body.
In order to get the vaccine mRNA into the vaccinee’s cells where they can do their job, they have to evade enzymes in the body that would naturally destroy them. The researchers protected the mRNA in the vaccine by wrapping it in a lipid bubble to prevent destruction. Other ingredients in the shots – such as polyethylene glycol, which is part of this lipid shell – can cause allergic reactions.
If I feel sick after my shot, does that signal a strong immunity?
Scientists have not found a link between the initial inflammatory response and the long-term response that leads to protection. There is no scientific evidence that someone with more obvious vaccine side effects is better protected from COVID-19. And there is no reason why an exaggerated innate response would make your adaptive response any better.
Both approved mRNA vaccines provided protective immunity for over 90% of recipients, but less than 50% reported a reaction to the vaccine and far fewer showed severe reactions.
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