Comparing Covid-19 Vaccines: Efficacy Rates and Side Effects

Over the past year, the Covid-19 pandemic has caused many of us to make certain lifestyle changes, both big and small. From working from home to avoiding communal areas, we have adapted our lives and refrained from social activities. This so-called ‘new normal’ seemingly took over our lives, at least until we finally started to see vaccines being developed by various companies and scientists that can curb infections, reduce the severity of the disease, and lower the risk of death.

Getting to Know Covid-19 Vaccines

Covid-19 vaccines are now being produced by various manufacturers around the world, with each company having their own production process. While each Covid-19 vaccine is unique, they are all made for the same purpose — to help build immunity and prevent the pandemic from spreading.

So far there are four types of Covid-19 vaccine:

1. Messenger RNA (mRNA) Vaccines Created from RNA genetic material, Covid-19 mRNA vaccines instruct our cells to produce a harmless protein that is unique to the virus. This triggers an immune response within the body, stimulating our immune systems to produce antibodies against the virus that can protect us from infection. Current mRNA vaccine options include Pfizer and Moderna.
2. Viral Vector Vaccines Viral vector vaccines use a genetically modified version of a different virus which has been injected with the Covid-19 virus’s genetic material. Once it enters the body, the vaccine mimics a natural infection, stimulating immunity and triggering the production of antibodies against Covid-19. As the body is being injected with a live virus, there are certain limitations for the immune-compromised when using these vaccines. Current companies producing viral vector vaccines include AstraZeneca, Johnson & Johnson, and Sputnik V.
3. Inactivated Virus Vaccines Inactivated virus vaccines use actual Covid-19 virus that has been killed or de-activated. When injected into the body, this doesn’t cause the actual disease, but instead triggers the immune system to recognize the presence of a foreign substance. Our bodies then produce antibodies against the Covid-19 virus in much the same way as the old hepatitis A and polio vaccines used to work. As this approach utilizes technology that has already been proven to work in people, it is generally considered to be a safer option for vaccination recipients, especially those with impaired immunity. Companies currently producing inactivated virus vaccines include Sinovac and Sinopharm.
4. Protein Subunit Vaccines Widely known and practiced Protein Subunit Vaccines have been proven to work in the past, including making hepatitis B and influenza vaccines. They involve mixing viral protein with immune-suppressants, thereby activating the body to create antibodies that fight the virus.

Effectiveness of Different Covid-19 Vaccines

- Pfizer: Approved by the World Health Organization (WHO), Pfizer is an mRNA vaccine that protects against the original Covid-19 strain (SARS-CoV-2). The vaccine has efficacy rates of 95% prevention against severe symptoms, and 100% prevention of death. However, there is not enough data yet to support whether or not it protects against further contagion by those vaccinated. The Pfizer vaccine prescribes two doses, three to four weeks apart. Infection is prevented from 12 days after the first shot.
- Moderna: Approved by WHO, Moderna is an mRNA vaccine that protects against the original Covid-19 strain, the UK Covid-19 strain (B.1.1.7), as well as the South African Covid-19 strain (501Y.V2). The vaccine has efficacy rates of 92% protection against severe symptoms and 100% prevention of death. There is no definitive information regarding how it protects against further transmission. Moderna prescribes two doses of the vaccine four weeks apart. Infection is prevented from 14 days after the first shot.
- AstraZeneca: A Viral vector vaccine, AstraZeneca is WHO-approved, and provides 63.09% protection against the original Covid-19 strain. There is still limited data as to whether the vaccine can prevent transmission. AstraZeneca requires two shots, administered eight to twelve weeks apart. (Those with severe immune imparity are not recommended to take this vaccine).
- Johnson & Jonson: Approved by the WHO, Johnson & Johnson is a viral vector vaccine that can prevent Covid-19 infection with 66.9% efficacy with a single dose. Within 28 days after the vaccination severe symptoms are prevented 85.4% and death is prevented 100%.
- Sinovac: This WHO-approved inactivated virus vaccine is 51% effective against Covid-19, with an efficacy rate of 100% against severe symptoms and death. There is currently no definitive information to support whether the vaccine is able to prevent further transmission. Sinovac prescribes two doses administered four weeks apart.
- Sinopharm: A WHO-approved inactivated virus vaccine, Sinopharm has an efficacy rate of 79% protection against the original Covid-19 strain. There is still no clear evidence showing that the vaccine can prevent further transmission. Sinopharm prescribes two doses three to four weeks apart.

Side Effects After Vaccination

All vaccines come with similar initial symptoms ranging from swelling to redness or itching around the injection area, headache, fatigue, fever, muscle ache, and occasional nausea and vomiting. Some people may also experience a severe allergic reaction. Symptoms should be monitored carefully for 30 minutes after the injection.
Here is a summary of reports of severe allergic reactions for each vaccine:
- Pfizer: The US Centers for Disease Control and Prevention (CDC) reports an average of 11.1 severe allergic reaction cases per 1,000,000 doses.
- Moderna: The US Centers for Disease Control and Prevention (CDC) reports an average of 2.5 severe allergic reaction cases, per 1,000,000 doses.
- WHO reports four cases of blood clots per 1,000,000 doses in the UK, and 10 cases of blood clots per 1,000,000 doses in the EU.
- Johnson & Johnson: WHO reports an average of 3.5 cases of blood clots per 1,000,000 doses.
- Sinovac: There have been reports that, in addition to initial side effects, those vaccinated with Sinovac have an increased likelihood of experiencing a loss of appetite, sore throat and runny nose as well as paralysis-like weakness in the limbs. More severe effects include narrowing of blood vessels in the brain. Reports show that there are on average 12 cases of severe allergic reactions per 1,000,000 doses.
- Sinopharm: The WHO has not yet reported any serious allergic reactions to this vaccine. Despite suspicions that the vaccine can cause blood clots, there is no conclusive evidence pinpointing whether this is an actual result of vaccination or simply cases of co-occurrence. Only 0.5-1.5 such cases are found per 100,000 doses.
All the vaccines mentioned above are effective in preventing outbreak of Covid-19. While they may lead to certain side effects in some individuals, they are still able to greatly reduce the rate of severe disease symptoms and prevent death. Nevertheless, although we now have vaccines to help us curb the pandemic, it is still important to take sound sanitary precautions. Let’s stay vigilant in wearing masks, regularly washing our hands, and maintaining a safe social distance. It’s still the only way to rid ourselves of this pesky pandemic once and for all.