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Millions of Americans are currently receiving coronavirus vaccinations as the US works to restore a sense of normalcy from the pandemic.

According to the Centers for Disease Control and Prevention (CDC), 33 percent of the U.S. population has received at least one dose and 19.4 percent has been fully immunized, either from Pfizer-BioNTech, Moderna or Johnson & Johnson.

However, some people have been wary of vaccination for fear of side effects such as fever or headache, while others have heard anecdotal reports of more extreme reactions, including a large rash on the arm or anaphylaxis.

Doctors say that serious reactions are rare and common side effects, such as pain at the injection site, are a sign that your immune system is building a response. spoke with three infectious disease experts about what side effects to expect from each COVID-19, why some people get them, and what it means.


The most common symptoms of the Pfizer vaccine are pain or swelling at the injection site, headache, fatigue, fever, chills, and muscle aches.

“ Somewhere between 20 and 80 percent of people will experience that, ” Dr. Richard Kennedy, a professor of medicine at the Mayo Clinic in Rochester, Minnesota, and co-director of the Mayo Clinic Vaccine Research Group, told .

“They are usually mild to moderate symptoms and last about a day or two.”

Dr. Thad Stappenbeck, chair of the Lerner Research Institute at the Cleveland Clinic, in Ohio, said that, in his experience, the most common side effect is headache.

‘Headaches are probably the most common and, anecdotally, of people I know who have been vaccinated,’ he told

Then there are rarer side effects, such as nausea, vomiting and swelling of the lymph nodes and armpits.

Kennedy says less than one in ten people will experience these side effects.

Finally, there are the rare allergic reactions to the vaccine, including hives, itching and swelling, and even anaphylaxis.

The most common symptoms of the Pfizer vaccine are pain or swelling at the injection site, headache, fatigue, fever, chills, and muscle aches. Pictured: bials of the Pfizer-BioNTech COVID-19 vaccine in Pfaffenhofen, southern Germany, January 15

Anaphylactic shock is a serious and potentially life-threatening reaction to an allergy from food, medicine, or even some type of material.

The immune system releases chemicals that flood the body, blood pressure suddenly drops, and the airways narrow, preventing a person from breathing normally.

Kennedy said about one in 100,000 people who receive the vaccine will experience such a reaction.

The good news, however, is that ‘it is reasonable rare and flightly treatable, ”he said.

For this reason, the CDC requires that vaccination sites check everyone 15 minutes after receiving their injection and those with a history of severe allergies for 30 minutes.

The doctors also add that people are more likely to have stronger reactions after the second dose, because the immune system is prepared to fight the virus and has a reaction after taking the last injection, only to realize that it is a is a false alarm.

As with the Pfizer vaccine, the most common side effects of the Moderna vaccine are injection site pain, fever, chills, headache, and fatigue.

“Mild fever, aches and pains, trouble sleeping on the first night, they’re flu-like symptoms,” Dr. Robert Murphy, an infectious disease specialist at Northwestern Medicine, in Chicago, Illinois, told

“They are self-limited and disappear within 48 hours.”

Another rare reaction, but only in Moderna patients, is the ‘Covid arm’, where people experience itchy and swollen skin, sometimes accompanied by red bumps.

Like Pfizer, people are more likely to have stronger side effects after the second dose.

A very small number of Moderna patients have also reported having anaphylaxis after their first dose.

“This is a well-documented phenomenon,” said Murphy. “They can have hives and swelling, but it’s a very small number.”

Some recipients – but only of the Moderna injection – have reported experiencing ‘Covid arm’, where people have itchy and swollen skin, sometimes accompanied by red bumps or hives.

But the stain is a harmless immune system response to the shot that disappears from the arm within a week.

The official term used by dermatologists and allergists to describe the side effect is ‘delayed skin hypersensitivity’.

“The vaccine pulls cells from the immune system to the injection site, so you see a rash, which goes away and within a day or two,” said Stappenbeck.

“It’s a bit troubling at first, but not significant and there are no long-term effects.”

As with the Pfizer vaccine, the most common side effects of the Moderna vaccine are injection site pain, fever, chills, headache, and fatigue. Pictured: Cartons containing the Moderna COVID-19 vaccine are being prepared for shipment to the McKesson distribution center in Olive Branch, Mississippi, December 2020


The single-dose coronavirus vaccine Johnson & Johnson has noticeably milder side effects than the Pfizer or Moderna vaccines.

“Almost across the board, fewer people are reporting side effects,” Kennedy said.

‘They are milder. The most common are pain at the injection site, which is not surprising given that it is a needle that enters your arm, which about 50 percent will experience. ‘

He said about a third of recipients report fatigue and muscle pain, 10 to 15 percent report nausea, and about 10 percent report swelling and redness at the injection site.

So why does J & J’s injection produce fewer side effects? Murphy said it’s because this vaccine is different from the other two.

J & J’s vaccine combines genetic material from the new virus with genes from the adenovirus – which causes the common cold – to trigger an immune response.

Relatively speaking, the Pfizer and Moderna vaccines use a newer platform, part of the pathogen’s genetic code called messenger RNA, or mRNA, to make the body recognize the coronavirus and attack it if a person becomes infected.

“They are very different mechanisms and different production processes,” said Murphy.

There have been no reports of anaphylaxis among J&J recipients, but Stappenbeck said it may be because fewer people have received the injection.

“It could just be a numbers game right now,” he said.

Side effects are much rarer in those who received the Johnson & Johnson vaccine, possibly due to the fact that it uses a different platform from Pfizer and Moderna. Pictured: Vials of the J&J vaccine during a vaccination surgery hosted by St John’s Well Child and Family Center in Los Angeles, California, March 25


As more vaccines have been administered, younger people have been reported to have more serious side effects than younger people.

The doctors say this because the immune system evolves as we age.

‘As we get older, everything to or about bodies doesn’t work so well and the immune system system is no exception, ”Kennedy said.

Data from clinical studies showed that young people reported more side effects after receiving vaccine doses than elderly people.

The reality is that younger people have stronger immune systems and when you’re older, you not such a big response, ”Murphy added.

However, it doesn’t mean that the elderly are not protected and that the vaccines are still just as protective for seniors as they are for young adults.


Women also report more side effects.

Women are more likely to report worse side effects after receiving COVID-19 vaccines than men, CDC data reveal.

Last month, officials looked at nearly 7,000 responses reported to the agency’s Vaccine Adverse Event Reporting System.

They found that nearly 80 percent of the reactions were reported by women, making them four times more likely to report an adverse reaction than men.

Kennedy said the reason behind this is a mix of biological and behavioral.

“Women’s immune systems behave slightly differently, they have a stronger antibody response,” he explained.

“They’re also more likely to go to the doctor when something is wrong, while men are more likely to try it out.”


All three doctors say the unequivocal answer is yes, you should get a COVID-19 vaccine as soon as it becomes available to you.

“The efficacy of these vaccines was remarkable,” said Stappenbeck.

Less than one percent of fully vaccinated people become infected later. That is better than the figures we received in the tests. we call this real-world data. ‘

Stappenbeck also encourages you to prepare for the possibility of side effects, such as being able to stop working the next day just in case and having enough water and Tylenol.

However, he suggests not taking the medication as a prophylactic.

“Wait until you have symptoms, if you have symptoms, then take it,” said Stappenbeck.

“The limit is four grams a day and you don’t want to overdose on Tylenol.”

The group also adds that potential side effects that you may have may be less worse than the possibility of getting COVID-19.

“You don’t know how sick you get until you get infected,” Kennedy said.

You may be asymptomatic or on a ventilator. Then you’ll say I wish I had gotten the vaccine and it’s too late by then

Reporting by Mary Kekatos, Senior Health Reporter for

This content was originally published here.