News·6 min read

What You Need to Know About the Top 3 COVID-19 Vaccines

Woman getting COVID-19 vaccine
May 12, 2022

COVID-19 has been in our lives for more than two years. And during that time, the US and other countries have signed off on a number of vaccines. Making way for us to start getting back to 'normal.' But as the pandemic continues, agencies like the CDC and FDA are rethinking some of their vaccine guidelines. So let's get into the vaccines that've made headlines — and why.

Vaccines with emergency use authorization or approval in the US


  • Status: Fully approved by the FDA for people 16 and older — making it the first COVID-19 vaccine to hit that milestone. It's also the first to get emergency use authorization for kids and adolescents ages five to 15.

  • Dose: Two doses, three weeks apart. The CDC recommends that immunocompromised people get a third dose at least four weeks after their second shot. Booster shots are available for certain groups five months after their second dose. Learn more about boosters here.

  • Efficacy rate: 91% within the first six months. After that, the effectiveness wanes (think: Down to around 44%). Which is why booster shots are recommended.

  • 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.


  • Status: Fully approved by the FDA for people ages 18 and up. The FDA was reviewing whether to extend it to teens 12-17. But put the decision on hold to check reports of a rare side effect (an inflammatory heart condition) from those who received the shot during its clinical trial.

  • Dose: Two doses, four weeks apart. Moderna has similar guidelines to Pfizer for third shots and boosters. Find out if you qualify here.

  • Efficacy rate: 93% within the first six months. Effectiveness wanes after that, but not as much as Pfizer’s (note: Around 84% efficacy.)

  • How it works: Moderna’s vaccine is injected into the upper arm. And it can last 30 days in a fridge. Like Pfizer/BioNTech’s vaccine, it uses cutting-edge mRNA technology.

  • Side effects: Similar to those reported with thePfizer/BioNTech vaccine.

Johnson & Johnson

  • Status: Limited authorized use. On May 11, the FDA said it’s tightening restrictions on who can get it because of reports around a rare but serious blood clot syndrome, in certain patients. Now, only people 18 years and older who don’t have access to other vaccines can get the J&J shot. Or those who wouldn’t otherwise get a COVID-19 vaccine — perhaps people who only want one shot. The CDC has also previously adjusted its guidance, recommending Moderna or Pfizer vaccines over J&J.

  • Efficacy rate: 76% for up to six months, before effectiveness wanes. 

  • 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 don’t forget about the blood clots mentioned above. The CDC says this reaction is rare. (Think: 60 cases out of the 18 million vaccinated with J&J.) But still enough to raise concerns. 

As of mid-May, more than 258 million Americans had at least one dose of the three vaccines. And while these are the approved vaccines in the US, they aren't the only ones that exist.

But, are the COVID-19 vaccines safe?

Yep. Health experts say they are safe and effective — proven by extensive clinical trials. But with so many vaccines being created at a fast pace, let’s talk about the development process. These vaccines go through stages of development and approval. 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. That’s because it’s when scientists are able to get more safety data since they are testing so many people. And can find less common, long-term, and rare side effects that might’ve been missed in previous phases. Scientists 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 these have been unusual times. And researchers have been able to combine phases to speed up testing. With the help of new technology and research of a virus similar to COVID-19 — plus, 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.


COVID-19 vaccines have helped Americans regain some sense of normalcy. But it’s not over yet, especially since 34% of Americans still aren’t vaccinated. Stay up to date on guidelines here, and check back here for updates on the top three most popular US vaccines.

Last updated on May 12 to include the FDA’s limitations on the J&J vaccine, as well as updated stats.

Last updated on Nov 2 to include the latest on the COVID-19 vaccines, including the FDA's emergency use authorization of the Pfizer vaccine for kids 5-11 and the CDC's approval for booster shots.

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