What you need to know about the top three vaccines

Published on: Dec 14, 2020fb-roundtwitter-roundemail-round
Sandra Lindsay, Coronavirus, COVID-19 vaccine, Pfizer, BioNTechGetty Images

COVID-19 pretty much shut down 2020. What's expected to put things back on track: vaccines. Right now, scientists are testing at least 52 COVID-19 vaccines in clinical trials on people. With an additional 162 vaccine candidates in preclinical trials being tested on animals, as of Dec. 10.

That seems like a lot

Sure is. But all of these vaccines are in different stages of development and approval. And with all the terms being thrown around, Phase 1, Phase 2, Phase 3, emergency use authorization, efficacy, it can be tough to figure out what all of this really means, and more importantly is it safe? So let's break it down. After researchers have identified a potential vaccine candidate they start the clinical testing process.

Preclinical testing...when scientists test the vaccine candidate on cells and then give it to animals to see if it creates an effective immune response.

Phase 1 (aka the safety trial)...when humans start to come in. A small number of people (20-100) are given the vaccine during this round. Scientists are testing for safety, best dosage amount, and to confirm that an immune response is being created. Approximately 70% of drugs will move onto the next phase.

Phase 2 (aka the expanded trial)...when hundreds of humans are given the vaccine candidate. And this time they are split into groups by health and demographics. Researchers want to know how the drug will affect different types of people. And scientists are keeping an eye out for how safe it is. Plus that the immune response is still going strong. Approximately 33% of candidates will move on to the next phase.

Phase 3 (aka the efficacy trial)…when scientists test the vaccine candidate on thousands of people to determine how well it works (hence efficacy). This is the phase we hear the most about because it provides the most safety data since it’s tested on so many more people. Scientists find less common, long-term, and rare side effects that may have missed in previous phases. And they are still testing for the tried and true immune response – which tells them whether the vaccine actually works. Approximately 25-30% of candidates move on from here.

Usually, this process can take years to complete, but because these are unusual times, researchers were able to combine phases to speed up testing thanks to things like new technology, years of research on a virus similar to COVID-19, and the financial incentives governments are providing to support this research. (Think: Operation Warp Speed.)

In the US, vaccine manufacturers need to get FDA approval before marketing and distribution can begin. And the steps for the approval process typically start after a successful Phase 3. A manufacturer presents their vaccine at “science court,” where a panel of independent experts act as a jury and pick apart the vaccine. If they're satisfied with the data, they endorse it and send it off to the FDA for final approval.

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Which is what Pfizer got?

Yep. Last week, the FDA authorized the Pfizer/BioNTech vaccine for emergency use in the US. But it's not the only one out there. Across the world, there are 13 vaccine candidates conducting Phase 3 trials. Here are the one's leading the pack:


  • Status: Recently, approved for emergency use in the US. Fully approved in Canada. Also has emergency use authorization in the UK and Bahrain.

  • Efficacy rate: 95%

  • Dose: 2 doses, 3 weeks apart

  • How does it work?: Pfizer/BioNTech’s vaccine is injected into the muscle. And must be stored at -94 degrees Fahrenheit. It uses genetic material called mRNA. Basically, this messenger (hence the 'm') delivers a piece of the coronavirus’s genetic code to the body’s immune system. The body uses that information to build spike proteins (the protein found on the surface of the coronavirus) and replicates it. After this process is complete, the immune system is now able to recognize the virus and attack it when it enters the body.

  • Side effects: No serious side effects. Some trial participants reported pain at the injection site and flu-like symptoms like fever, chills, and body aches. But UK health officials are saying people with a "significant history of allergic reactions" should hold off on getting this vaccine after two health care workers had adverse reactions after getting the first dose.


  • Status: Phase 3. It's applied for FDA emergency use authorization on Nov. 30. But it's waiting to hear back. Until then, it's already got deals in place with the US, Canada, Japan, and Qatar to supply the vaccine once they get the OK.

  • Efficacy rate: 94.5%

  • Dose: 2 doses 4 weeks apart

  • How does it work?: Moderna’s vaccine is injected into the muscle. And it can last 30 days in a fridge. Like Pfizer/BioNTech’s vaccine, it uses cutting edge mRNA technology.

  • Side effects: So far, Moderna has noted that participants have felt pain at the injection site, muscle aches, and headaches.


  • Status: Phase 3

  • Efficacy rate: Ranged from 62-90%

  • Dose: 2 doses 4 weeks apart

  • How does it work?: Unlike the previous two, the AstraZeneca-Oxford vaccine uses a harmless cold-causing virus that scientists have modified to include genetic material from the coronavirus. And similar to the Pfizer/BioNTech and Moderna vaccines, once injected it’ll stimulate an immune response so the system can learn to recognize the virus.

  • Side effects: In Phase 1 and 2 no serious side effects were detected. Full data from their Phase 3 trial is yet to be released.

  • Important note: This vaccine is the cheapest of the three. It can be stored at normal fridge temperatures. And it's easy to make. But a series of data blunders have left some doubting its ability to stand up to public and scientific scrutiny.

So what can Americans expect?

A lot. The CDC recommended that the US’s approximately 21 million health care workers and 3 million long-term care residents get first dibs on the Pfizer/BioNTech vaccine (which is slated to arrive in all 50 states today). Some health care workers have already started to receive it. And the general population should be eligible to receive the vaccine by spring or later. But ultimately states make the final call on who will receive the vaccine and where shots are administered. Meanwhile, President-elect Joe Biden vowed to distribute 100 million shots in his first 100 days in office. And he may be able to achieve this goal if Moderna’s vaccine is also approved by the FDA. And if chains like CVS, Walgreens, and Walmart start taking steps to distribute the vaccine as well.


While we’re seeing giant leaps and breakthroughs happen at a rapid pace in the COVID-19 vaccine race, it’s important to remember that the majority of us will not get a vaccine until next year. But hope is contagious and these vaccine developments are signaling a possible return to normal by next year. In the meantime, it’s important to continue using safety precautions to stop the spread until the vaccines are ready for distribution here in the US.

Skimm'd by Kamini Ramdeen and Niven McCall-Mazza

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