(CN) — As the United States closes in on three months of the Covid-19 vaccine rollout, more than 57 million people have been able to receive at least one shot. The recent authorization of the Johnson & Johnson vaccine means more Americans will be able to make an appointment soon.
Compared to the previously approved Pfizer and Moderna vaccines, based on messenger RNA, the J&J vaccine works slightly differently. As a result, the side effects expected may vary, too — but many reactions, like fluish symptoms, are common to all three vaccines.
The main side effect patients report is pain around the injection site, said Kim Litwack, professor and dean of the University of Wisconsin-Milwaukee’s College of Nursing.
“This is true for dose one and two,” Litwack explained — and it can occur with the one-dose J&J vaccine too.
When a vaccine is injected, the body’s immune response jumps into action, responding to the presence of a foreign entity. So it follows that the response may be most intense around the source of the intruder: a needle in the arm.
Fatigue, headaches, muscle and joint aches and fever are all potential side effects as well. In short, it might feel like you have the flu. Those symptoms are similar in all vaccines, but in the two-dose vaccines, they are more common after the second shot.
Pain can be managed with acetaminophen, like Tylenol, or ibuprofen, Litwack said. Rest and drinking fluids can help with fatigue and fever.
However, you shouldn’t premedicate before heading to a vaccine appointment, said Todd Brown, instructor and vice chair of Northeastern University School of Pharmacy’s Department of Pharmacy Practice.
“You shouldn’t take something before getting the vaccine,” Brown explained, "because that depresses the immune system in the body” — meaning the vaccine may not work as effectively.
Side effects should all be short-lived: They typically start well within a day of getting vaccinated, and may last up to three days.
Adverse Reactions
As with any medicine, there’s a possibility of having an allergic reaction to a Covid-19 vaccine.
Allergic reactions could be more common with the Moderna and Pfizer vaccines, Brown explained, because of the technology used to develop them, which relies on genetic material called mRNA.
While researchers say that mRNA opens up new possibilities in medicine, the fragile material easily breaks down. To protect the mRNA-based vaccines, scientists bubble-wrapped the Pfizer and Moderna vaccines at the molecular level, packaging them in lipid nanoparticles, or tiny globs of fat.
The chemical that makes up the lipid molecules, polyethylene glycol — which is also used to make laxatives — seems to be causing most allergic reactions to the vaccines. The Pfizer and Moderna vaccines are the first mRNA-based vaccines authorized for use, “so that’s why it’s the first time we’re seeing this type of thing,” Brown explained.
Even so, the risk of vaccine allergy is “extremely low,” Litwack said. In data submitted to the Centers for Disease Control and Prevention in January, there were 2.1 cases of anaphylaxis per million doses of the Moderna vaccine, and 6.2 cases for the Pfizer vaccine.
“As more doses are given,” Litwack said, “this rate appears to be dropping even lower.”
Most reactions occurred within 15 minutes of receiving the vaccine, and most people who had a reaction also had a history of severe allergies or anaphylaxis.
“These vaccines are extremely safe,” Litwack said.
While the J&J vaccine doesn’t have the same potentially allergenic lipids, its recent introduction leaves some room for unknowns. Experts say it's too soon to say whether J&J vaccine side effects will differ from the others in the U.S. in a meaningful way.