Concern about side effects is the leading reason many Americans are wary of getting a coronavirus vaccine, but experts say side effects are common with any vaccine, and a sore arm, fatigue or headache is far better than getting sick with COVID-19.
"There don’t appear to be any unexpected side effects," said Dr. Wafaa El-Sadr, a professor of epidemiology and medicine at Columbia University. "They are the side effects you’re used to with other vaccines."
Side effects are "a sign that your body is building an immune response associated with the vaccine, and that’s what you’re trying to do," said Onisis Stefas, chief pharmacy officer at New Hyde Park-based Northwell Health.
A Kaiser Family Foundation poll released Dec. 15 found that concern about side effects is the top reason that more than one in four Americans said they probably or definitely won’t get a vaccine, even if it’s free and scientists say it’s safe. A September Pew Research Center poll found similar concern.
The U.S. Food and Drug Administration reviewed side effects for vaccines developed by Pfizer and BioNTech, and by Moderna and the National Institutes of Health, before this month giving emergency use authorization for the two vaccines.
The vaccines caused similar side effects, with pain at the injection site on the arm the most common, reports by an FDA independent advisory committee of experts said. In addition, a majority of clinical trial subjects had fatigue and headaches. Muscle pain, chills and joint pain were next among common symptoms.
"There’s nothing there that stands out to me as alarming, and they’re happening when they’re supposed to happen, which is early on after vaccination," El-Sadr said. "And they’re not lasting for a long time. They resolve usually by themselves in a day or two."
The rare cases of severe side effects — such as severe allergic reactions of a few people to the Pfizer-BioNTech vaccine — also are common with other medications, said Dr. Bettina Fries, chief of the infectious diseases division at Stony Brook Medicine.
"You can never guarantee a patient they won’t have an adverse reaction when you give them a new medication," she said.
That’s why anyone receiving the vaccine will be monitored for 15 minutes, because severe reactions typically occur within that period of time, and why New York pharmacists are required to have epinephrine on hand to treat severe allergic reactions, Stefas said.
Coronavirus vaccines work in different ways, but what they and other vaccines have in common is that they try to trick the body into thinking the vaccine is a harmful pathogen, so the body can create disease-fighting antibodies.
The immune system can’t tell that the vaccine is beneficial, Stefas said.
"It sees it as a foreign body and basically attacks it," he said. "That’s how you build that immune response, and that’s how you build antibodies that have memory, which will give you that level of immunity over time."
Memory means that if there is a real infection with the coronavirus, the body will have antibodies ready, he said.
The side effects signal the body is working hard to fight what it perceives as a threat, although the absence of side effects doesn’t mean the vaccine isn’t working, Stefas said. People react differently to vaccines.
Side effects to the Pfizer-BioNTech and Moderna vaccines were more common after the second required dose, clinical trials found.
The body’s immune system was "already activated, so it gets even more activated by the second dose," Fries said.
The Pfizer-BioNTech and Moderna vaccines use mRNA, or messenger RNA. The mRNA instructs cells to create a harmless piece of a coronavirus protein, and the immune system starts to make antibodies against it, according to the U.S. Centers for Disease Control and Prevention.
The next two vaccines expected to come before the FDA for approval, likely by February — from Johnson & Johnson, and from the University of Oxford and British-Swedish company AstraZeneca — use a different technique.
In the Johnson & Johnson vaccine, nonreplicating, harmless genetic material from the coronavirus is put inside adenoviruses, which cause the common cold but are inactivated, according to the company. The immune system then creates antibodies. The Oxford-AstraZeneca vaccine works roughly in the same way.
Health practitioners must report any potential severe vaccine reactions to the FDA, which will look for trends, Stefas said.
One challenge will be determining whether a health problem is caused by a vaccine or has other roots, said Dr. David Battinelli, Northwell’s chief medical officer.
"Let’s say we vaccinate a million people," he said. "Those million people are going to get illnesses. They’re going to have heart attacks, they’re going to have strokes. They’re going to have appendicitis. They’re going to have all these things. So people need to be extremely careful and cautious and have to figure out, is there any cause and effect? You’re going to have to try to figure out what’s from this and what’s not. That’s a big task."
El-Sadr said any side effects from vaccines must be balanced with the benefit of immunity to the coronavirus.
"We know how deadly COVID-19 can be," she said. "On the benefit side, we have vaccines that have 95% effectiveness, which is remarkable. The benefits far outweigh the risks."
The vaccines' side effects
Most people who took the two federally authorized COVID-19 vaccines reported side effects that ranged from pain where they received the injection to muscle and joint pain.
From the Pfizer-BioNTech vaccine
- Injection-site pain, redness or swelling: 84.1%
- Fatigue: 62.9%
- Headache: 55.1%
- Muscle pain: 38.3%
- Chills: 31.9%
- Joint pain: 23.6%
From the Moderna-National Institutes of Health vaccine
- Injection-site pain: 91.6%
- Fatigue: 68.5%
- Headache: 63%
- Muscle pain: 59.6%
- Joint pain: 44.8%
- Chills: 43.4%
SOURCE: U.S. Food and Drug Administration, Vaccines and Related Biological Products Advisory Committee