A side by side comparison of Covid-19 vaccines: Pfizer/ BioNTech vs Moderna

"Kathryn Chia" "Apothekathryn" "Covid-19" "Vaccine"

Since the Covid-19 pandemic began, groups of scientists from all over the world have been racing to develop a vaccine, in the hopes of saving millions of precious lives. The Pfizer and Moderna vaccine are two key mRNA vaccines, that have been approved in various countries. Although there are differences between the two, their most important similarity is that they have both been proven to be safe and effective. It is also important to note that in clinical trials, both Pfizer and Moderna vaccines had very large numbers of participants, exceeding the required sample of 10,000 participants by a mile, with Pfizer having more than 43,000 participants and Moderna having more than 30,000 participants.

Pfizer/ BioNTech Vaccine

The Pfizer vaccine or the BNT162b2 was manufactured by Pfizer Inc and BioNTech and was approved for use in the UK for those aged 16 and above in early December 2020.

Moderna Vaccine

The Moderna vaccine or the mRNA-1273 was manufactured by ModernaTX, Inc and was approved for use in the UK for those aged 18 and above in early January 2020, but the company has since begun testing its vaccine on 12-17 year olds.

Comparing the 2 Vaccines…

Storage and Delivery

Both vaccines require 2 doses of shots to the muscle of the upper arm, 28 days and 21 days in between doses for Moderna and Pfizer vaccine respectively.

They both have different compositions and thus require different storage requirements. The Moderna vaccine is much easier to store, only requiring a normal fridge with a temperature of 2°C to 7°C. It can be stored at this temperature for up to 30 days and is stable at room temperature for 12 hours. The Pfizer vaccine is much harder to store, requiring a special freezer at -80°C to -60°C. This means that for the time being, the Moderna vaccine is infinitely more accessible, while the Pfizer vaccine can most likely only be distributed at hospitals or clinics in developed countries with special freezers.

mRNA vaccines

The Moderna and Pfizer vaccine are both mRNA vaccines. This means that instead of receiving a weakened form of the virus, triggering an immune response, these vaccines give our cells instructions to make a harmless spike protein (which is found on the surface of the Covid-19 virus), provoking our immune systems to begin building an immune response and making antibodies. This mRNA vaccine cannot give someone Covid-19, as it does not contain the live virus of Covid-19 and does not interact with our DNA in any way as it never enters the nucleus of our cells, which is where our DNA is kept. The cell also quickly breaks down the mRNA after the harmless spike protein is produced.

"Kathryn Chia" "Apothekathryn"

Although it is a new type of vaccine, it is not to be feared. Researchers have already been working on mRNA vaccines for decades and they have been studied before for flu, Zika, rabies and cytomegalovirus (CMV).


Both vaccines have similarly high efficacies. Upon receiving both doses of the vaccine, the Moderna vaccine is 94.1% effective, while the Pfizer vaccine is 95%. These vaccines have a much higher efficacy rate as compared to a standard flu vaccination, at 70%. Experts say that this will provide immunity from the virus for at least a year, but more data is still needed to provide a clearer timeline.

Allergic reactions

Both trials, with Pfizer having more than 43,000 participants and Moderna having more than 30,000 participants included many people with a history of various allergies, with the only exclusion being people who were known to have allergies to components of the vaccine. In the trial, there were no issues of anaphylaxis. As of 6/1/21, out of the 1,893,360 first doses of the Pfizer vaccine, only 21 cases of anaphylaxis occurred, which is a mere 0.0011%. In the very rare cases of an allergic reaction, one would be able to go to a doctor’s office easily to get treated promptly, an alternative worlds better than contracting Covid-19, where there is no good treatment yet.

Side effects

The Moderna vaccine is slightly more reactogenic, which means that you’d get more symptoms from it. However, this may suggest that the body is producing more antibodies and may be why it is also slightly better at preventing severe Covid. On the other hand, the Pfizer vaccine was less reactogenic and had a slightly higher efficacy. Some symptoms by those who received the vaccine included Fatigue, Injection site pain, Muscle Pain, Joint Pain, Chills and Fever. In both vaccines, serious adverse events are very rare at less than 0.5% and these have not yet been proven to be linked to the vaccination. Nevertheless, it must be remembered that side effects from these vaccinations are perfectly normal signs that your body is building protection against the virus and are in no way an indication that the vaccine is unsafe. They are temporary and self-resolve within a few days. To date, there have been no serious long term side effects proven to be associated with either vaccine.

Does the vaccine cause Bell’s Palsy?

There has been speculation that the vaccine can cause Bell’s Palsy – a temporary paralysis of one side of the face. In the Moderna trial with more than 30,000 participants, there were 3 cases of Bell's Palsy in the vaccine group and 1 in the placebo group, while in the Pfizer trial with more than 43,000 participants, there were 4 cases of Bell’s Palsy in the vaccine group. The frequency of Bell’s Palsy in these groups is even less than the general population and hence no causal relationship can be drawn between Bell’s Palsy and the vaccine. Even so, if Bell’s Palsy was to be linked to the Covid vaccine, it is still a treatable condition. When compared to the alternative of life-threatening Covid, these potential side effects and Bell’s Palsy are unquestionably a superior option.

Despite their differences, both vaccines are brilliant at preventing the transmission of the virus and represent spectacular scientific breakthroughs in the field of vaccines. Together with the Oxford-AstraZeneca vaccine, they have been approved for use in the UK. Hopefully, all vulnerable groups in the population will be vaccinated against Covid-19 very soon. In the meantime, 65 more Covid vaccines are currently in clinical trials on humans, and 20 have reached the final stages of testing.

"Kathryn Chia" "Apothekathryn"

Find out more about Covid-19 here, on the NHS official website.


1. https://www.cdc.gov/coronavirus/2019-ncov/vaccines/different-vaccines/Pfizer-BioNTech.html

2. https://www.cdc.gov/coronavirus/2019-ncov/vaccines/different-vaccines/Moderna.html

3. https://www.bbc.com/news/health-51665497

4. https://www.cdc.gov/mmwr/volumes/70/wr/mm7002e1.htm

5. https://www.pfizer.com/news/hot-topics/the_facts_about_pfizer_and_biontech_s_covid_19_vaccine

6. https://www.standard.co.uk/news/health/how-does-vaccine-coronavirus-oxford-work-b73816.html

7. https://www.biospace.com/article/experts-say-benefits-of-covid-19-vaccines-far-outweigh-risks-of-reported-temporary-side-effects-/

8. https://www.nytimes.com/interactive/2020/science/coronavirus-vaccine-tracker.html

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