Vivid dreams and COVID arms: The weird vaccine ‘side effects’ you’re experiencing are likely harmless

Some of the expected side effects of COVID-19 vaccines include a sore arm, fatigue and a mild fever – but what about strange dreams?

While there is an abundance of anecdotal reports of odd side effects from the vaccines, few are proven to be caused by them. And though COVID-19 vaccines are reported to have more intense side effects than a regular flu shot, this is merely a sign that your immune system is doing its job.

Side effects are analyzed throughout an extensive clinical trial process when a vaccine is in development. This is typically divided into three phases.

Phase 1 involves a small number of participants to “assess safety, toxicity and dosage,” says Catharine Chambers, an epidemiologist and public health researcher. “Once we’ve determined that the vaccine among that very, very small subset is safe, we then go into a Phase 2 study. Phase 2 trials are typically where we start (…) looking at how the immune system responds to the vaccines.”

The U.S. Food and Drug Administration’s (FDA) second phase is described as an expansion of the first and is similar to Canada’s. According to the Centers for Disease Control’s website, the vaccine is given to individuals who match characteristics “similar to those for whom the new vaccine is intended.” Phase 3 involves dosing tens of thousands of participants to test the vaccine for efficacy and safety.

Image provided by Health Canada

Side effects are closely monitored at each stage. Typically, to seek approval in the American market, vaccine developers must use the FDA toxicity assessment scale. With this, side effects and other adverse events are broken down into four separate categories: mild (grade 1), moderate (grade 2), severe (grade 3) and potentially life threatening (grade 4).

For a vaccine to be approved by the FDA, reactions in clinical trials must be mostly mild and moderate. 

One of four charts in the FDA’s toxicity grading scale. Graphic by Miranda Caley.

Side effects also are categorized as local or systemic reactions. Local reactions are specific to one part of the body, such as pain where the vaccine is injected; systemic reactions are felt throughout the body, like a fever or fatigue. These side effects are common in almost any vaccination, but especially so for COVID-19 vaccines.

Even after the third phase of clinical trials and the beginning of a vaccine’s distribution to the public, vaccines continue to be monitored and reviewed to confirm their safety and that their benefits outweigh the risks. It is only when the vaccine is widely distributed that rarer or abstract side effects might come to light.

Pfizer-BioNTech, Moderna, AstraZeneca-Oxford and Janssen have all reported similar side effects with their COVID-19 vaccines: redness, pain or swelling at the site of injection, fatigue, headache, muscle pain and fever. However, as millions of people are vaccinated, other potential side effects have become the subject of online discourses, leaving many wondering if the medical mysteries they’re experiencing are linked to their vaccinations. Here are five frequently described ones and what we know about them so far:

1)   Lymphadenopathy

Swollen lymph nodes have been reported by Moderna, Pfizer-BioNTech and AstraZeneca-Oxford. Recent research has found those reporting this side effect experienced it in the axilla (basically the arm pit) of the injected arm several days after vaccination. While swollen lymph nodes may be worrisome at first, this has been deemed as a perfectly normal reaction that will fade, with 11.6 per cent of patients in Moderna’s trials and 0.3 per cent of Pfizer-BioNTech’s patients reporting swelling after their first dose. Lymph nodes are an essential part of the immune system, housing white blood cells to fight infection. If the swelling persists or other health issues coincide with it, a trip to the doctor may be needed.

2)   COVID arm

Some say they have experienced “COVID arm” from the Moderna vaccine in particular. Researchers at Massachusetts General Hospital (MGH) found that Phase 3 clinical data from the Moderna trial shows “delayed skin hypersensitivity” in a small number of more than 30,000 participants. The large, red and sometimes raised, itchy or painful skin reactions were not fully explained. In clinical observations of 12 patients with COVID arm, the side effect appeared between four- and 11-days post-vaccination and lasted about eight days.

“For most people who are experiencing this, we believe it’s tied to the body’s immune system going to work,” says Esther Freeman, director of Global Health Dermatology at the hospital.

“COVID arm” is not a verified side effect of Moderna’s vaccine. If it’s experienced after receiving a dose, it should go away on its own in about a week. If it continues to persist or happens quickly after receiving a dose and spreads to the rest of your body, it may be a severe allergic reaction that should be cared for immediately.

3)   Other skin reactions

Similarly, eczema flare-ups have been anecdotally reported. However, the National Eczema Society says there is no substantial evidence to indicate COVID-19 vaccines worsen underlying skin conditions.

Facial swelling was very rare in clinical trials for Moderna, but three participants who had received dermal filler injections reported to have developed it after receiving the vaccine. Two had received fillers in their cheeks and subsequently experienced facial swelling. The third had a history of lip injections and developed a swollen lip; however, they reported having a similar reaction in the past following an influenza vaccine. In each case, the swelling remained local and resolved itself after treatment with steroids or antihistamines.

In a December report on the Moderna vaccine, the FDA says, “It is possible the localized swelling … is due to an inflammatory reaction from interaction between the immune response after vaccination and the dermal filler.” This reaction has not been listed as a verified side effect of any vaccines, though clinical trials continue to explore the possibility of more side effects.

4)   Vivid dreams

A bizarre experience many are discussing online is strange or vivid dreams. While it could be coincidental, it’s not entirely uncommon for medications to contribute to intense dreaming. Various other medications, including antidepressants, beta blockers, Parkinson’s disease drugs, blood pressure medications and drugs to stop smoking have all been reported to cause intense dreaming.

However, it could simply be because you’re finally getting enough sleep. Fatigue is a common side effect of every approved COVID-19 vaccine thus far and it may cause you to sleep longer than you normally do. Heavy dreaming usually occurs during rapid eye movement (REM) sleep, which cycles every 90 minutes as you sleep, lasting up to 25 minutes. If you sleep longer, you’ll experience more REM sleep and potentially more vivid dreams.

The likelihood of weird dreams is increased if a low-grade fever is added to the mix. “Fever dreams” is a common saying for a reason, so it’s understandable that someone would enter an intense dreamworld after getting the jab.

5)   Menstrual cycle changes

A major discussion taking place online recently is about menstrual cycles seemingly changing post-vaccination. From more intense cramps to a heavier period, many are wondering if COVID vaccines have an impact on their cycles – but the only evidence we have is purely anecdotal. While no studies have been conducted yet on whether the vaccines are partially responsible for these changes, there are several logical reasons for experiencing a shift.

Womb lining is a part of the immune system – its immune cells create, maintain and break down the lining, which is what sheds during a period if an egg isn’t fertilized. Vaccinations cause an immune system to kick into gear, which could lead to spotting or premature lining shedding.

But don’t worry: temporary changes to menstrual cycles have also been seen in people after getting the flu or HPV vaccines as well. There have been no long-term side effects, and current evidence is that COVID-19 vaccines in particular do not affect fertility and are safe for pregnant people.

“During the years that someone could get pregnant, precaution should be taken with certain live virus vaccines (…) The COVID-19 vaccines in use are not live virus vaccines. There is no biological reason to believe that the current (vaccines) could impact someone’s ability to get pregnant,” says Ottawa Public Health.

Vaccines also cause an inflammatory response in the body, which encourages it to produce antibodies and other cells to fight disease. A link between inflammation and menstruation has been distinguished in the past, with studies suggesting people with signs of inflammation from infections generally experience more painful periods.

“The current evidence does not suggest an increased risk of either menstrual disorders or unexpected vaginal bleeding following the vaccines,” says the Medicines & Healthcare products Regulatory Agency’s latest weekly report.


It’s important to remember that COVID-19 vaccines have been deemed safe and effective by many international regulatory agencies, including Health Canada and the FDA, and that several of these anecdotally reported side-effects have not been proven to be caused by COVID-19 vaccines.

The reasons some reported symptoms often aren’t caught in clinical trials are simple: sample sizes are drastically smaller in even the largest of trials compared to the world’s population; and it’s difficult to prove or rule out causation without rigorous epidemiological studies.

We should expect to learn about rarer potential side effects as more people get doses, which is why we need robust safety monitoring. It’s also why vaccine guidelines are updated over time.

“That’s why things like blood clots (…) only got picked up once we started rolling out these vaccines to the entire population,” says Chambers. “These very, very rare events that are happening in the order of one in 10,000 – or even one in a million – aren’t going to get picked up in a clinical trial where you’ve only got 40,000 people enrolled.”

As with any drug, there is a small but serious chance of a severe allergic reaction called anaphylaxis, which can be easily treated with an EpiPen. This is why you are observed for 15 minutes after receiving the vaccine; up to 30 minutes is recommended for people who have a history of allergic reactions and/or anaphylaxis.

But most of these rarer post-vaccine experiences have a simple explanation: Your immune system is doing what it is supposed to do.

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  • K o H T F says:

    I’ve taken drugs to quit smoking as well as antihistamines in high doses as anti anxiety. Doctors told me to stop taking those. Or atleast the nicotine pouch I saw that I had exceeded my use for it. Regardless this Pfizer vaccine is the only other drug I’ve had this intense of an affect with as far as vivid dreaming. So I encourage everyone who has gotten the vaccine to track whether they’re waking up in the middle of the night during vivid dreams.

  • Steve Martin says:

    I had my Pfizer shot on Friday the 27th of August, Sunday morning my sore arm is almost better but suffered severe lethargy for a day. Last night, the 28th I had bizarre dreams & diarrhoea at midnight. Both of which rarely happen. Sue, I hope you get better soon.

  • Sue says:

    I’m writing this at 3am as I lay awake, unable to sleep due to catching my breath and sleep starts which I’ve had pretty much every night since I took this vaccine. It was Pfizer, which I was assured was the ‘safest’ one. I’m reading your article which says I should have had a ‘better sleep’. That’s not what’s happening. It’s been about a week and 2 days, and it’s only the first dose. Yet this injection has affected every inch of my body like no other vaccine I’ve ever had. Every day I have a total energy crash and can’t keep my eyes open, and every night I can’t sleep due to palpatations, night starts, over-alertness, muscle twinges and pins and needles in the oddest places. (Like the side of my face). I have a full time job I need to do. I really feel like it’sabsolutely crazy that I’m required to take another shot of this, and I’m honestly dreading it. I genuinely could cry. I have no history of any medical issues whatsoever and have never been on any medication. Is this really fair? Oh just to add, the couple of hours I did manage to sleep, I got one of those lovely night terrors you mentioned. It was horrific and made me very alert until I had to get up.

    • Miakota says:

      Having vivid nightmares where I can’t go back to sleep and heart pain After 2.5 weeks after first Pfizer which I did not have before. .
      I am wondering if this will subside.

      I hope you feel better Sue and everyone else out there having any reactions from mild to severe.

  • Richard J. Sullivan says:

    Ahm, I think you left out death and swollen heart as a side effect. YOU BETTER SUPPLEMENT YOUR STORY.

    I’m serious.

  • Mohit kumar says:

    Mohit kumar

  • LN says:

    I’m surprised that Healthy Debate published an article (on such an important topic) that was written by a mere journalism student with no medical background. In all her ‘wisdom’, she attempts to assuage readers that reports of ‘odd’ side-effects to the Covid-19 vaccines are merely ‘anecdotal’ thereby implying that there is no basis for inquiry or concern. She really has no business writing this as there are, in fact, many reports of serious side-effects in all age groups. I have to wonder why she is trying to hoodwink the general public into thinking there is absolutely nothing to worry about. People need to be fully informed before they consent to immunization. The author has obviously not done any serious or thorough research. A lot can be written about Covid-19 vaccine side-effects, and Healthy Debate chose this??? Why?


Miranda Caley

Editorial Intern

Miranda Caley is a fourth-year journalism student with a minor in women’s and gender studies. Originally from Newfoundland, she moved to Ottawa for her studies to learn about the rich and diverse cultures across Canada.

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