Mild side effects are common after being vaccinated against COVID-19, but for people receiving dose regimens, the strongest symptoms are more common after the second shot.
Side effects can include headache, fatigue, pain, fever, and nausea. They are usually mild and go away in just a few days, according to federal health officials.
But why would the side effects be more intense after the second dose? Health experts say it has to do with how the immune system responds to the virus.
Pfizer-BioNTech and Moderna vaccines, the two-dose vaccines available, are mRNA vaccines that work by using genetic code to teach the body to produce a protein that establishes an immune response that helps generate antibodies.
When people who have never been exposed to COVID-19 are vaccinated before, their immune system recognizes the protein as strange and responds to it, but it is not very strong, said Dr. Beth Kassanoff, a northern internal medicine doctor. of Texas Preferred Health Partners and president of the Dallas Medical Society.
With the second dose of the vaccine, a person’s immune system “remembers” the protein and responds more aggressively.
“When you get the second vaccine, you will have a much more robust immune response because your body already has some of these antibodies,” he said. “They are ready to fight the infection.”
While this response can cause flu symptoms, it is actually a good sign and means the vaccine is doing its job.
But at the same time, people who have no side effects don’t have to worry, Kassanoff said. The lack of side effects does not mean that your body does not respond to the shot.
“I’ve seen people of all ages, some of whom had quite significant discomfort, low-grade fever and fatigue,” he said. “And then one of my partners, who is 50 years old, had zero side effects compared to the second. At first, he worried a little, but later he checked his antibodies and responded well. It was very interesting, you can’t really predict. “
Health experts are still learning more about why some people experience more intense side effects than others, but say age and past exposure to COVID-19 are factors.
“One pattern we see constantly is that older people have fewer side effects than younger people. We really don’t know why,” said Katelyn Jetelina, an epidemiologist at UTHealth School of Public Health in Dallas. “The other pattern we’re seeing is the one that COVID has had before and the vaccine has more serious side effects. That makes sense because that means they have a certain level of immunity and the body recognizes the antibodies to that vaccine and react ”.
Kassanoff said he heard reports of COVID-19 “long carriers” or people with symptoms that last a long time after they stop testing positive for the virus and that their symptoms resolve a little after the vaccine.
But health experts say the details of these trends are not yet known.
“I take care of whole families of people, like parents and adult children and all that kind of stuff, and everyone has a completely different response,” Kassanoff said. “Even within the same family, even with about the same age, even with about the same genetics, sometimes people respond more.”
This trend is not specific to the COVID-19 trait; even with other vaccines, some people respond differently than others, he said.
As more people get vaccinated, more information will be known about the side effects of the vaccine, health experts say.
While Jetelina said the side effects of the second dose may seem intimidating, people should not let them deter themselves from getting vaccinated.
“It’s discouraging, I’ll say, to sign up to get sick,” he said. “Not everyone gets sick and honestly most people don’t get sick, we just hear about these terrible people or cases where people get sick. What I say is suck it up, take a Tylenol and take the day off and it will clear up. I promise it will be clarified.