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Wednesday, October 27, 2021

Pfizer, Moderna and AstraZeneca vaccines: Whats the difference?


As several countries around the world roll out their inoculation programmes, questions about the different brands of vaccines have surfaced. Here is all you need to know about the Pfizer, Moderna and AstraZeneca vaccines.

A year ago, the world embarked on an endeavour to develop safe and effective vaccines for Covid-19. Today, and in record time, a few vaccines have now been authorised by relevant authorities, leading to the biggest global vaccination campaign in history.

More than 181 million doses of Covid-19 vaccines have already been administered worldwide across 79 countries. The latest rate recorded by Bloomberg falls at roughly 6.19 million doses a day. 

All vaccines are similar in that they work by exposing the human body to molecules that, in turn, trigger an immune response. These can be small fragments of the disease-causing organism, or “blueprints” that signal the body to make these small fragments. 

The learned immune response is stored and “memorised” by our bodies and this enables them to react quickly and to produce antibodies when exposed to the same germ again. 

Read also: Myths vs facts: Your biggest vaccine worries extinguished

Vaccines, in general, can cause some mild and temporary side effects. When it comes to the Covid-19 vaccines, these side effects are mostly limited to injection-site pain, headache and fatigue. 

These potential side effects are signs that the vaccine is triggering an immune response and are not related to the safety of the vaccine. 

All manufacturers go through regulatory approval, and candidate vaccines are continuously and rigorously assessed for their safety and efficacy in animals first and in humans. Vaccines that fail safety tests cannot progress into clinical trials. 

To date, approximately 10 vaccines for Covid-19 have been authorised or approved for use around the world, while over 200 vaccine candidates remain under development, according to December 2020 figures from the World Health Organisation. These vaccines can be categorised based on the method of exposure to the virus that was used.

Whole virus vaccine

This type of vaccine uses a technology that has been around for years. It is well established and can be used for people with weak immune systems. It uses either a deactivated or weakened form of the disease carrying pathogen (microorganisms that cause diseases for example a virus or bacterium).

This causes the body to kick-start its immune response. Whole virus vaccines are relatively simple to manufacture. Approved vaccines Sinopharm and Sinovac are examples of whole virus vaccines.

RNA or mRNA vaccine

This is a novel technique, as there are no other existing approved vaccines (for diseases other than Covid-19) that use it.

However, scientists have been testing and studying mRNA vaccines for many years. They can be developed faster than the traditional vaccines since they are created in a laboratory with readily available material – meaning that process can be standardised and scaled up.

Read more: Is there a vaccine for WhatsApp’s ‘infodemic’?

Once injected into the body, the mRNA vaccine teaches our cells how to make “spike proteins” which are proteins that are found on the surface of the virus that causes COVID-19.

Once these spike proteins are made and displayed on the surface of the cells, the body’s immune system then recognises that these proteins are foreign and starts making antibodies as part of an immune response against the infection. The body here learns how to protect itself against future infection. 

Non-replicating viral vector

In this type of vaccine, a safe, genetically modified version of the virus is injected known as the “vector”. In the case of the Covid-19 vaccine, the vector here is the spike proteins that are found on the surface of the virus. This again, triggers an immune response against the created antigens.

Protein subunit

Subunit vaccines don’t use the whole microbe or a safe version of the virus but use only the parts (or subunits) of a virus or bacterium that the body’s immune system needs to recognise and kick-start its response. This type of vaccine is used widely especially for childhood vaccinations such as those protecting against diseases such as tetanus and whooping cough.

To date, there are no approved COVID-19 vaccines that use this technique with Novavax being the candidate that is closest to getting approved for use in the UK.

The three main frontrunners are the vaccines that were developed by (in no specific order) Pfizer/BioNTech, Moderna and Oxford/AstraZeneca. While it is unlikely that most individuals will have a choice on which vaccine to take, knowing some of the main differences between them could prove useful. 

Pfizer/BioNTech Moderna AstraZeneca
Type mRNA vaccine mRNA vaccine Non-replicating viral vector
Efficacy 95% 94.5% 62-90%
Storage, distribution and shelf life Storage requirement of between -60 to -80 degrees Celcius (ultra-cold freezer). At this temperature it can be stored for up to 6 months. Can be kept in a refrigerator for up to 5 days, and in a dry ice chest for 30 days.

Challenging distribution due to reliance on freezers that can store at subzero temperatures.

Should be stored at -20 degrees Celcius (standard freezer). Can be kept in a standard refrigerator for up to 30 days and at room temperature for up to 12 hours.

Less challenging to distribute than Pfizer vaccine as storage is at a higher temperature and there is no need for ultrafreezer.

Stored at standard fridge temperature for at least 6 months.

The use of a typical fridge for storage means the vaccine can be kept at healthcare facility for more time and allows for easier distribution/remote and rural access.

Standard method of administration 2 injections, 3 weeks apart 2 injections, 4 weeks apart 2 injections 4 weeks apart

New research findings suggest that the vaccine’s efficacy increases when the second dose is administered >12 weeks after the first. More research needed to confirm significance of these findings.

Approximate cost per dose (US figures) $20 $15-25 $4
Production projections Goal to produce 2 billion doses in 2021 Up to 1 billion doses for 2021 Currently producing 100 million doses per month. Intention to double this by April 2021. However, variants are presenting a threat to progress.


It is important to note that there are no research findings that support the ranking of “best Covid-19 vaccines”, and it is important not to get too caught up in trying to compare them. All vaccines go through rigorous and thorough tests for safety. They all protect, and they all help pave the path toward the end of the pandemic.

For us to reach this desired end point, vaccines must be combined with social distancing, mask wearing and hand washing for them to work as effectively as possible.

Read also: PPEs are protecting us but harming our environment

Manufacturers must also work on making their vaccines easier to store and transport by making them storable at higher temperatures, to ensure universal, equitable access and allocation.

Maha El Akoum, MPH, is a public health professional currently working as Head of Content at World Innovation Summit for Health [WISH].

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