Covid-19 Vaccine Side Effects Showdown: Pfizer vs. Moderna

published on 07 March 2021

As a global consumer health safety and community reporting website, we receive a wide range of reports on our site. Since the launch of the Covid-19 vaccines we have accumulated reports relaying peoples' experiences after taking the vaccines. We analyzed, and categorized the results so far, so we can share back to our community and others who may find this helpful. 

We hope that by sharing this information, people will feel better informed on the range of possible outcomes as they move ahead with their vaccinations, and for those who have been vaccinated already, there may be some comfort in knowing that you are not alone in experiencing certain side effects.

A percentage breakdown of reported side effects:

Percentage breakdown of Covid-19 Vaccine Side Effects. Source: Safelyhq.com
Percentage breakdown of Covid-19 Vaccine Side Effects. Source: Safelyhq.com

To categorize reports we used the following approach:

  • None: User stated they had ‘no side effects’
  • Mild: typically just soreness and side effects described as ‘mild’ by the users. 
  • Strong: Unusual or notable description, which includes trips to ER, or intense reactions. 
  • Medium: Is everything that falls in between mild and strong.

Important: The focus of this story is the comparison between Moderna and Pfizer, please see our data notes at the bottom about reporting bias & data skew, we are not concluding that only 13% of vaccine recipients will escape side effects.

Side effect breakdown, Pfizer vs Moderna:

Covid-19 Vaccine Side Effect Comparison - Pfizer vs Moderna. Source: Safelyhq.com
Covid-19 Vaccine Side Effect Comparison - Pfizer vs Moderna. Source: Safelyhq.com

We more commonly saw reports with no side effects from Pfizer, and where Pfizer side effects were reported they were more commonly reported as mild vs Moderna.

What are the most commonly reported side effects?

Of people who experienced side effects,  the most common mentions are shown below. We excluded soreness as this was common to the majority of reports. 

The Most Commonly Reported Covid-19 Vaccine Side Effects. Source: Safelyhq.com
The Most Commonly Reported Covid-19 Vaccine Side Effects. Source: Safelyhq.com

What is the side effect breakdown in Moderna vs Pfizer? 

Top 10 Side Effect Mentions Comparing Pfizer & Moderna Source: Safelyhq.com
Top 10 Side Effect Mentions Comparing Pfizer & Moderna Source: Safelyhq.com

This shows the top 10 mentions by vaccine (again excluding soreness). Moderna has more mentions of each side effect. Moderna has a lot more side effect mentions per report - in total  60% higher than Pfizer. 

Which countries have we received reports from so far?

Covid-19 Vaccine Side Effects Reports by Country. Source: Safelyhq.com
Covid-19 Vaccine Side Effects Reports by Country. Source: Safelyhq.com

Which states within the US participated so far?

We have received reports from most states in the US - with the highest participation coming from California, Texas, and Florida. 

Source of US Covid-19 Vaccine Reports by State. Source: Safelyhq.com
Source of US Covid-19 Vaccine Reports by State. Source: Safelyhq.com

Where can I see the reports and raw data? 

You can view the reports on our covid-19 vaccine landing page here. If you would like raw data extracts to do your own analysis please contact us at [email protected]

I got a Covid-19 vaccine, how can I participate and share my experience? 

We welcome you to share your experience simply go to our covid-19 vaccine landing page and fill out the form as show below. To start click here

How to share your Covid-19 Vaccine experience on safelyhq.com
How to share your Covid-19 Vaccine experience on safelyhq.com

What are some sample reports ?

A sample 'No Side Effects' report: 

Long Island City, Queens, NY, USA
I am a teacher and am authorized to get the Moderna vaccine. I made an appointment in Ridgewood 2 days ago. Appoint was at 5:20 but didn't get my shot until 7:40. The lines are extremely long at night. But the nurse said they are empty in the morning. Once you get inside it is very fast, everyone is very helpful and you can sign up for your second vaccine. They make you wait 15 mins to make sure you're ok before you leave. I have no side effects from the shot and feel fine.
— Reported By SafelyHQ.com User January 14, 2021 8:51 PM

A sample 'Mild' report:

Syracuse, NY, USA
Symptoms: Soreness
I just finished getting my second Pfizer Covid-19 vaccination 1 week ago, and the only side effect I had was a sore arm, from both of them. Many of my coworkers got fever, chills, headache, and vomiting. But not me. I had absolutely nothing.
— Reported By SafelyHQ.com User January 18, 2021 5:19 PM

A sample 'Medium' Report: 

Sevierville, TN, USA
Symptoms: Headache, Chills, Fatigue, Joint Pain, Muscle Pain, Soreness
Moderna first vaccine 12/23/20. Arm felt sore a little worse than a tetanus shot. Felt pretty fatigued the next two days afterwards. Second Moderna vaccine 01/20/21. Arm felt sore pretty much within a couple of hours. The next day had hot/cold chills, muscle/joint pain and headache. The 2nd day my injection site was red/warm to touch and has spread quite a bit. Showed the Covid screeners and they said that this is common after the 2nd shot. Took Tylenol and will continue to watch.
— Reported By SafelyHQ.com User January 22, 2021 1:14 PM

A sample 'Strong Side Effects' report:

Pittsburgh, PA, USA
Symptoms: Headache, Soreness, Skin Rash
Morning recieved: Arm sore. Headache. Then broke out in welt type hives from my face down to my toes. Had to go to ER for epi pen and steroids.
— Reported By SafelyHQ.com User February 1, 2021 4:52 PM

What can I do to help?

  • Share your vaccine experience! If you had a vaccine, our community would love to see your report, as we continue to get reports, we will update and expand our analytics. To share you experience click here.
  • Share this article! The more people are able to read other people's experiences, the more we can help others on their vaccination journey.

How can I stay up to date with your work on Covid-19 Vaccines? 

You are welcome to sign up to our email list. Learn about new analysis ,   get the latest news, and get updates as new reports come in. To sign up click here.

What about Oxford, Johnson & Johnson and the other Vaccine Brands?

We have received reports for other vaccines but  so far there is not enough data to include in this analysis. We would love you to share your experience if you had one of these vaccines. To share your experience click here.

Notes about the data

  1.  This data represents a sample of 250 vaccine recipients, 125 Moderna, and 125 Pfizer, from the US, Canada, and the UK (primarily US)  between January 1st 2021 and March 5th 2020.
  2. This data is likely skewed toward older recipients and/or higher risk populations as they have been the priority recipients of vaccinations so far in the US.
  3. To the extent that there is reporting bias whereby those people who experience side effects are more likely to share their experience than those with no side effects - the overall 'no side effects' numbers may be under reported. However, all other things being equal, the relative comparison between Pfizer and Moderna may still reflect a fair comparison.

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