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A Comparison of Vaccines Available


And What We Still Don’t Know


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As we head into the next phase of the pandemic, questions are still arising about the vaccines available on the market and how they differ.

What Vaccines Are Available Today?



Moderna and Pfizer were the first two vaccines available in the United States for wide distribution and have many similarities. Both are mRNA vaccines. Unlike traditional vaccines that carry microorganism components or live-but-relatively inactive microorganisms — such as bacteria or viruses — mRNA vaccines carry a genetic code for a component of the microorganism (in the case of COVID, a component of the viral spike protein).

Cells in the immune system use this genetic code to make the viral spike protein. The immune system, which has the capacity to recognize self and non-self proteins, becomes sensitized and ready to mount a more vigorous response to the spike protein when the immune system comes into contact with the virus.

The mRNA vaccines carry the advantage of being able to sensitize the immune system without having to introduce whole bacteria or virus. They also have a shorter manufacturing time. Because the genetic code can be used as a template, it is easier to manufacture these vaccines on a large scale.

Pfizer vs. Moderna


While Pfizer and Moderna are both mRNA vaccines, they have a few subtle differences.


Pfizer’s vaccine has two doses administered 21 days apart, whereas Moderna’s vaccine has two doses administered 28 days apart. Moderna’s vaccine may be shipped at -4°F (standard freezer temperature), making this vaccine easier to transport. The side effect profile is similar for both vaccines — people may feel worse after the second dose with both Moderna and Pfizer.

Pfizer is also available for use in younger patients (age 16) while Moderna is available for people over the age of 18. Contraindications to both vaccines are similar as well. It is recommended for patients with a history of serious allergic reactions to vaccine ingredients such as polyethylene glycol and polysorbate to avoid both vaccines.


What Other Vaccines Are in the Market?

Other vaccines are also available or in the process of obtaining approval. AstraZeneca, for example, has a vaccine that uses a genetically altered cold virus for chimpanzees that contains the spike protein mutation found in the COVID virus. AstraZeneca's vaccine is 70 percent effective while Pfizer and Moderna both report around a 95 percent efficacy.

Additionally, other vaccines are currently under study or being released. Jansen uses genetically modified viruses, but their vaccine only requires a single dose and reports a 66-72 percent efficacy rate. A single-dose vaccine may have useful application in places where access to health care, including follow-up, are limited.

Novavax, a two-dose vaccine, uses a spike protein, which, in turn, elicits an immune response. Results from Novavax vaccine trials confer an 89 percent efficacy rate.

These clinical trials in all, show multiple effective vaccines. However, initial trials have been mostly based on the original strain of the virus. What is largely unknown is the efficacy of each of these vaccines against each virus strain.

Do These Vaccines Actually Work?


There are some data on certain vaccines and how effective they are against different mutations. For example, Novavax has an efficacy rate of 50 percent against the African strain, and Johnson and Johnson reports a 50 percent efficacy rate against the South African strain.


Other strains have developed and circled across the globe as well. The UK variant is reported to be more than 50 percent more infectious than the original strain, and certain vaccines have been less effective against it as well. While initial reports are available about the efficacy of some vaccines against the UK strain, overall, more comprehensive data is needed to determine the true efficacy of each of these vaccines against current strains, as well as any other strains that may arise in the near future.

Interestingly, the UK is currently conducting studies to determine the efficacy of combining different vaccines in an effort to maximize the efficacy of the vaccines against various strains. In the future, this may help tailor vaccine regimens against dominant strains, but currently, the effect of this is largely unknown.


What's Next?


With only about one year into the pandemic, vaccines are already available, a great scientific success. Over time, as research progresses, we will develop a greater understanding of how these vaccines can be useful in protecting human civilization from this disease.

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