What You Need to Know About the Top COVID-19 Vaccines

Published on: Aug 23, 2021fb-roundtwitter-roundemail-round
Sandra Lindsay, Coronavirus, COVID-19 vaccine, Pfizer, BioNTechGetty Images

COVID-19 shut down 2020. What's turning things around in 2021: vaccines. There are a handful of shots available around the world, and much of the US has reopened as more than half of the US population is fully vaccinated. But variants are throwing a wrench in those plans.

Remind me, which vaccines has the US signed off on?

The FDA has given the thumbs up to three vaccines: Pfizer/BioNTech, Moderna, and Johnson & Johnson. Here’s what you need to know about each one…


  • Status: Fully approved by the FDA – making it the first COVID vaccine in the US to reach that step.

  • Dose: Two doses, three weeks apart.

  • Efficacy rate: 95%. Pfizer says the vaccine is more than 91% effective six months after the second dose. Research from the UK shows it’s about 88% effective against the delta variant.

  • How it works: The vaccine must be stored at -94 degrees Fahrenheit. It’s injected into the muscle, and uses genetic material called mRNA instead of DNA to send an alert to the immune system. Basically, this messenger delivers a piece of the coronavirus’s genetic code to the body’s immune system. The body then uses that information to build spike proteins and starts replicating them. After this process is complete, the immune system is able to recognize the virus and attack it when it enters the body. Note: mRNA vaccines do not alter your DNA.

  • Side effects: Recipients have reported pain at the injection site and flu-like symptoms (think: fever, chills, body aches) that could be worse after the second dose. There have also been reports of people having allergic reactions to the vaccine in the US and UK, and in April the National Institutes of Health started a study to look into those reactions. If you have severe allergies (think: require an EpiPen after exposure to an allergen), you may want to talk to your doctor before getting this shot. 


  • Status: Approved for emergency use for people ages 18 and up. Moderna has applied for full FDA approval and is waiting for a status update from the agency.

  • Dose: Two doses, four weeks apart.

  • Efficacy rate: 94.5%. Similar to Pfizer, Moderna says its shot is more than 90% effective after six months. It’s unclear how effective the vaccine is against the delta variant after two doses (early research from Canada suggests it’s 72% effective after one dose).

  • How it works: 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: Moderna recipients have noted similar side effects to the Pfizer/BioNTech vaccine.

Johnson & Johnson

  • Status: Approved for emergency use for people ages 18 and up. Johnson & Johnson is planning to apply for full FDA approval later this year.

  • Dose: 1 dose.

  • Efficacy rate: In US clinical trials, it showed a 72% rating. But its protection rates in countries where the virus’s variants have become dominant showed a lower rating. (Think: 57% in South Africa.) The efficacy rate against the delta variant isn’t clear, but one study shows that the J&J vaccine isn’t as effective when it comes to the delta variant. And The New York Times says that’s consistent with a single dose of AstraZeneca’s vaccine – which is similar in structure to J&J and only has a 33% efficacy rate against symptomatic illness from the delta variant.

  • How it works: J&J’s vaccine can be stored for up to three months at regular fridge temps – making it easier to ship. The vaccine is injected into the arm. And uses a genetically-modified adenovirus (which would normally cause flu and cold symptoms but can’t in this case since it’s been altered). Think about it like this: the adenovirus is the delivery van for the vaccine. Inside the van, is double-stranded DNA – which has the instructions to create spike proteins (aka the protein found on the surface of the coronavirus). 

    • Let’s get more specific: Once it’s injected, the adenovirus enters a cell in the body to deliver its message (aka the DNA) to the cell’s nucleus (where the genes are stored). From there, the cell reads the DNA and converts it into messenger RNA (mRNA). Now, the cell is vaccinated and can alert the rest of the immune system, replicate the spike protein, recognize the virus, and create antibodies to protect against coronavirus.

  • Side effects: J&J’s vaccine appears to be less likely to trigger allergic reactions. And the main side effects appear to be pain at the injection site, fever, fatigue, and headache. But a number of people have reported serious issues after receiving the vaccine, including potentially life-threatening blood clots (found in at least 28 cases) and a rare neurological disorder called Guillain-Barré syndrome (found in about 100 cases). For context: more than 13 million Americans have gotten a J&J shot.

As of early August, about 70% of American adults have received at least one dose of these three vaccines – a major milestone that President Biden set to achieve by July 4. But they’re not the only ones that exist around the world.

What other vaccines are out there?

  • Novavax. The vaccine, which is given in two doses three weeks apart, is about 90% effective. It was part of former President Trump’s Operation Warp Speed (aka the initiative aiming to speed up the development and distribution of COVID-19 vaccines). Novavax is planning to seek emergency use authorization in the US later this year. It said it could manufacture 150 million doses per month by the end of the year – and has reportedly committed to supplying more than 1 billion doses to developing countries. More research is needed on how it works against the delta variant.

  • AstraZeneca-Oxford. The vaccine, which is given in two doses four weeks apart, is about 76% effective. It’s been approved for emergency use in the UK, EU, Canada, and COVAX (which aims to bring more than 2 billion vaccine doses to poorer, developing countries) – and is expected to file for emergency use authorization in the US. The good news is that this vaccine has the cheapest price per dose compared to the three vaccines authorized in the US. It can be stored at normal fridge temperatures and it's easy to make. But AstraZeneca has run into a few issues, including reports of rare blood clots after vaccinations. Researchers in the UK found that this vaccine is about 67% effective against the delta variant.

  • Sinopharm. The vaccine, which is given in two doses three to four weeks apart, has a 78% efficacy rate. In May, it became the first vaccine made in China to get emergency use authorization from the World Health Organization. Millions of doses have been donated to countries around the world – and the company that produces it could reportedly ship up to 1 billion doses by the end of the year. But breakthrough cases in the Seychelles have worried some about Sinopharm. In the spring, the island country – which at the time was the most vaccinated country in the world – experienced a spike in COVID-19 cases. And most of the people inoculated there got a Sinopharm shot, raising questions about the vaccine’s effectiveness. Plus a recent study from Budapest shows that the vaccine offers poor protection among the elderly. And another study found it was less effective against the delta variant.

As of Aug 20, there are at least 112 COVID-19 vaccines in clinical development, with an additional 184 vaccine candidates in preclinical trials. But the real question on everyone’s minds are...

Are the COVID-19 vaccines safe?

With so many vaccines being created at a fast pace, first we have to dive into the development process. 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. So let's break it down. After researchers identify 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.

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 then 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.


In a matter of months, the US has managed to get a significant amount of its population vaccinated. But the country isn’t quite at herd immunity yet. And according to Our World in Data, only 1.4% of people in low-income countries have gotten at least one dose. COVID-19 isn’t a US-only problem – it’s worldwide. So until there’s vaccine equity and access around the world, we should still remain vigilant against the virus and its variants.

Last updated on Aug 23 – Updated to include that the FDA has fully approved Pfizer’s COVID-19 vaccine.

Last updated on Aug 4 – Updated to include the efficacy rates of vaccines against the delta variant and the latest news on FDA approvals.

Skimm'd by Maria Martinolich, Kamini Ramdeen, and Niven McCall-Mazza

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