Covid19 Vaccines: What are the Effects, Side Effects, Efficacy, & Complications of Different Vaccines

COVID-19 has incited panic among people for several reasons. Coronavirus being the novelty of the virus and people not becoming immune to it, have caused a huge impact on the world’s population. As the death toll increased among the infected individuals, researchers put their utmost effort to end this menace by developing vaccines against this novel virus. 

Many different vaccines have been developed worldwide and have been effective to great extents against COVID-19. COVID-19 death and infection rate have considerably dropped after the vaccines have been administered to the world’s population. However, different vaccines have different efficacy rates. Let us dig deeper to look into the details of some of the most effective vaccines.


After their positive clinical trial data reporting, Pfizer was the first company to receive the Food and Drug Administration (FDA) Emergency Use Authorization (EUA). Pfizer vaccine is an mRNA vaccine that consists of genetic information of an integral part of SARS-CoV-2, i.e., COVID-19 virus and is known as the ‘spike protein’. These proteins are little projections on the virus’s surface. 

This is the actual vial of the Pfizer vaccine


Clinical trials have provided strong evidence of the high-level efficacy of the Pfizer vaccine. A trial involving 43,548 individuals reported that 95% protection was conferred against COVID-19 in participants aged 16 years and above after the second dose of vaccine. 

The results have been proven consistent all over the world. The vaccine has reduced the COVID-19 symptomatic cases by 94% and reduced severe illness by 92%. 

No. of shots: 2


The vaccine must be stored at the temperature of -80°C to -60°C. Therefore, ultra-cold freezers are required for the storage of the Pfizer vaccine. However, it can also be stored at -25°C to -15°C, for up to 2 weeks. 

Side effects:

These symptoms indicate the effectiveness of the vaccine. 


Some of the less common side effects are:

  • muscle pain
  • joint pain
  • nausea
  • swollen lymph nodes
  • allergic reactions

Some of the severe allergic reactions are observed in rare cases: 

  • breathing difficulties
  • dizziness
  • rapid heartbeat
  • rash all over the body
  • swelling of the face and throat
  • weakness


Moderna vaccine is the second after Pfizer to become the authorized vaccine in the U.S. for emergency use. The biochemistry is similar to that of the Pfizer vaccine, as it is also an mRNA vaccine. This vaccine sends instructions to the body cells to make a spike protein to train the immune system to identify and destroy the actual virus when it enters the body. 


Moderna vaccine has reported 94.1% of the efficacy rate against the SARS-CoV-2 in a trial involving 30,420 adult participants. 

31,069 vaccinated individuals were compared with 31,069 unvaccinated individuals. The vaccine was proven to be 88.7% effective in preventing the COVID-19 infection. 

No. of shots: 2


Moderna vaccine must be stored between -25°C to -15°C temperature. However, the vaccine can be stored in the refrigerator before use, between 2°C to 8°C for up to 30 days. 

Side effects:

These side-effects are usually observed after the second dose and can last for a few days. 


Some of the rare side-effects include anaphylaxis: 

Other rare side effects include myocarditis (inflammation of the heart muscle) and pericarditis (inflammation of the tissue surrounding the heart).


Janssen/J&J vaccine is quite different from Pfizer and Moderna vaccines. Janssen vaccine is also known as the carrier or virus vector vaccine. It uses a different approach to train human cells to produce SARS CoV-2 spike proteins. 

photo credits:


The Janssen vaccine is 66% effective in protecting people from Covid-19. It has reportedly reduced the symptoms and death rates. 

No. of shots: 1


The multi-dose unpunctured vials of the Janssen vaccine against COVID-19 are stored at 2°C to 8°C. Unpunctured vials of the vaccine can be 9°C to 25°C for up to 12 hours.

Side effects:

  • Pain
  • Redness
  • Swelling
  • Tiredness
  • Headache
  • Muscle pain
  • Chills
  • Fever
  • Nausea


Some of the rare side effects include:


Sinovac is a whole virus vaccine that uses a deactivated or an attenuated form of the SARS CoV-2 that causes COVID-19 to trigger protective immunity to it. 

A vial of the Sinovac Biotech Covid-19 vaccine. Source: AFP/Getty Images


In clinical trials worldwide, Sinovac inactivated virus vaccine has been (50% to 79%) effective in preventing Covid infection symptoms. However, it is 100 % effective against severe COVID-19 infection.

No. of shots: 2


The vaccine is to be stored in a refrigerator at 2°C to 8°C. It must not be frozen and must be protected from light. It should not be kept at room temperature more than 25°C.

Side effects:

  • Muscular pain. 
  • Swelling
  • Burn at the injection site. 
  • Headache
  • Fatigue
  • Fever
  • Cough
  • Dizziness


Some rare side-effects include:

  • muscle spasms
  • eyelid edema
  • nose bleeds
  • abdominal distension
  • constipation
  • hyposmia
  • hot flashes
  • hiccup
  • conjunctival congestion 


Vaccination against COVID-19 is putting an end to the COVID-19 pandemic. This is not going to happen overnight. WHO and many such organizations are working tirelessly to develop and deliver effective and safe vaccines worldwide. Although vaccines are game-changing tools, we must not stop taking preventive measures such as maintaining a safe social distance, wearing masks and washing hands to avoid COVID-19 as the variants exist and may get stronger with time. 


  1. Thomas, K. (2020). New Pfizer results: Coronavirus vaccine is safe and 95% effective. The New York Times18.
    1. Meo, S. A., Bukhari, I. A., Akram, J., Meo, A. S., & Klonoff, D. C. (2021). COVID-19 vaccines: comparison of biological, pharmacological characteristics and adverse effects of Pfizer/BioNTech and Moderna Vaccines. Eur. Rev. Med. Pharmacol. Sci25(3), 1663-1669.
    1. Li, Q., & Lu, H. (2020). Latest updates on COVID-19 vaccines. BioScience Trends14(6), 463-466.
    1. Meo, S. A., Bukhari, I. A., Akram, J., Meo, A. S., & Klonoff, D. C. (2021). COVID-19 vaccines: comparison of biological, pharmacological characteristics and adverse effects of Pfizer/BioNTech and Moderna Vaccines. Eur. Rev. Med. Pharmacol. Sci25(3), 1663-1669.
    1. Mahase, E. (2020). Covid-19: Moderna vaccine is nearly 95% effective, trial involving high risk and elderly people shows. BMJ: British Medical Journal (Online)371.
    1. Mahase, E. (2021). Covid-19: U.K. approves Moderna vaccine to be given as two doses 28 days apart.
    1. Crommelin, D. J., Anchordoquy, T. J., Volkin, D. B., Jiskoot, W., & Mastrobattista, E. (2021). Addressing the cold reality of mRNA vaccine stability. Journal of Pharmaceutical Sciences110(3), 997-1001.
    1. Tregoning, J. S., Brown, E. S., Cheeseman, H. M., Flight, K. E., Higham, S. L., Lemm, N. M., … & Pollock, K. M. (2020). Vaccines for COVID‐19. Clinical & Experimental Immunology202(2), 162-192.
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    1. Mahase, E. (2021). Covid-19: Unusual blood clots are “very rare side effect” of Janssen vaccine, says EMA.
    1. Baraniuk, C. (2021). What do we know about China’s covid-19 vaccines?. bmj373.

Comments (12)

  • Kat

    July 29, 2021 at 8:19 am

    Almost all vaccines have its side effects. Whether fully vaccinated or not, one must continue steps to help prevent the spread of COVID-19 such as staying at home, wearing a mask, practice social distancing and so on just to be sure. Stay safe always.


    July 29, 2021 at 11:55 am

    Spent months waiting for a vaccine schedule, but until now, nada. I just really wanna be vaccinated but why wont any of my registrations push through? Huhuhhhuhu

  • Ivan M. Jose

    July 29, 2021 at 2:21 pm

    I love how informational your post is. People need to read this and be educated as a lot of individuals are still apprehensive to get vaccinated. I’ve completed my doses and I could attest to the side effects — I got chills and aches on both occasions.

  • WanderWoMom

    July 29, 2021 at 2:40 pm

    mine is astra zeneca.. ang di naman ako nilagnat ng grabe. chilled the first night, pero nainitan din. pinaka effect sakin, body ache talaga!!! tapos ang tagal mawala nun masakit na braso! pero im happy naka 1st shot na ako. tagal pa ng 2nd. sana mag fully dosed na ako.

    any vaccine is the best one! so one me opportunity, kailangan igrab niyo na di niyo alam howother people are waiting so hard for their turn tapos ang daming umaayaw. 🙁 di nila alam na we need to have herd immunity, the whole world. para mawala na ito

  • Polly

    July 29, 2021 at 2:57 pm

    I’d like to thank you for making this information accessible and easy to understand. Sadly, there are a lot of people who refuse to get the vaccines – mainly because they do not understand how it works and fear the side effects. I’ve completed mine this month and I feel a little bit safer compared to a few months ago.

  • May Palacpac

    July 29, 2021 at 3:50 pm

    You’re right, it won’t be an overnight thing. We really need to sit it out and be patient until then. I had my first dose of Astrazeneca this month. Our second dose would be on September. I hope I don’t have to go through the same side effects again as the first one was terrible!

  • Blair Villanueva

    July 30, 2021 at 1:22 am

    All vaccines will give you side effects and depended na yan sa health mo if you will experience it or not. When I got my Pfizer vaccines, I felt no side effects, the same experience when I got my annual flu shots.

  • Kurt Everfresh

    July 30, 2021 at 3:12 am

    Thank you for this informative blog about vaccines! I hope everyone gets vaccinated sooner so we can achieve herd immunity already.

  • Hyejin

    August 2, 2021 at 1:01 am

    Now I understand more about the vaccines and am not afraid anymore to get a shot. Hopefully, all the people in the world can receive the vaccine sooner.

  • Rimi

    August 23, 2021 at 7:58 am

    This is so well-thought out and really helpful, thank you!

  • Jenna

    September 5, 2021 at 12:09 am

    Unfortunately I know ppl who had severe reactions to 3 of these shots but I won’t say which 3 just bc they all had history of vaccine reactions so it’s something that probably wouldn’t happen to the average person…. so my only advice Is if you have a history or a family history of adverse reactions to vaccines or allergic reactions to vaccines please proceed with caution

  • Hyun Jang Nim

    December 6, 2021 at 8:32 am

    I love this. Complete po. Very helpful. Mine is sinovac. Minimal lang naman side effects. stay safe po.

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