What We Know About the Top COVID-19 Vaccines So Far

What We Know About the Top COVID-19 Vaccines So Far

There are dozens of potential COVID-19 vaccines in full development worldwide, but only a handful have made the shortlist of most promising, and only three at the time of this writing have released late-stage trial data on how effective they are in preventing coronavirus infections.

As countries begin authorizing the use of these vaccines for the general public, here’s what we know so far about the top COVID-19 vaccines and what we know about the companies working on them.

Understanding the COVID-19 Vaccines and the Development Process

Before we get too far, we need to clarify a few important terms and concepts concerning the COVID-19 vaccines and the process that goes into developing and approving these vaccines.

mRNA Vaccines

Two of the leading vaccine candidates are mRNA vaccines, which is a new type of vaccine. 

Usually, vaccines work by injecting a weakened or inactivated version of the disease into your body. Doing so triggers your immune system to protect against that disease. 

Luckily, your immune system will remember that response for a while (exactly how long varies). That means that when or if your immune system encounters that same disease in your body in the future, it’s prepared to respond and stop the infection quickly.

mRNA vaccines work a little differently. Messenger RNA (mRNA) is basically a template that teaches your cells how to make a specific protein. 

So instead of injecting a version of the disease-causing virus or bacteria like in other vaccines, an mRNA vaccine gives your body a template to learn how to make proteins associated with the coronavirus. 

Your body makes those proteins as instructed, and then your immune system builds its immune response based on those proteins, just like with other vaccines.

The proteins that the mRNA helps your cells create will stay separate from each other. That means they can’t form a complete version of the coronavirus. 

But because they’re a significant and recognizable part of the coronavirus, your body will know exactly how to respond and shut down the infection when the virus enters your body.

Additionally, even though the mRNA teaches your cells how to make a protein, it never enters the nucleus of the cell and therefore can’t change the DNA of your cell. These templates are also of limited use, so once your cell has followed the template and made its proteins, it’ll get rid of the mRNA. 

Vaccine Development Process

Once vaccines enter into human testing trials during the vaccine development process, they go through three phases of volunteer trials. 

  • Phase I trials are generally small groups of less than 100 healthy volunteers. 
  • Phrase II trials go to several hundred volunteers who are selected based on a specific set of characteristics that will best represent the people who will eventually get the vaccine.
  • Phase III trials are given to several hundred or thousands of volunteers.
  • Phase IV trials are ongoing-trials that monitor the safety and efficiency of the vaccine.

Phase I and Phase II trials or Phase II and Phase III trials can happen simultaneously. 

Once a vaccine completes its Phase III trial, the data collected from that trial goes to the regulatory review and approval process. 

Vaccine Approval Process

In the United States, the federal government organization in charge of approving new vaccines for use by the public is the U.S. Food and Drug Administration (FDA).

But first, all of the trial data from the vaccine development and testing process goes in front of an advisory board made up of experts outside of the FDA called the Vaccines and Related Biological Products Advisory Committee. 

This 17-member panel reviews all the data available on the vaccine to determine whether or not it works and if it’s safe enough for the general public to get.

Based on the analysis, the advisory panel votes whether or not to recommend the approval of the vaccine to the FDA. If that vote passes, then the panel passes on the official recommendation to the FDA, who will then make the final decision on whether or not it will grant emergency authorization approval

The Top COVID-19 Vaccines

Now that we’ve gone over the important terms and concepts related to the COVID-19 vaccines and how they’re developed and approved, here’s what we know so far about the top COVID-19 vaccine candidates. 

Pfizer and BioNTech

Vaccine type: mRNA

Efficiency in preventing the coronavirus: 95% effective

How many doses: 2 equal 30-microgram doses with the second one 21 days after the first dose

Side effects: Flu-like symptoms, including fever, headaches, muscle pain, chills, or reactions at the injection site. Additionally, as the vaccine was rolled out to the public in the United Kingdom, two recipients with noticeable histories of severe allergic reactions had adverse allergic reactions to the vaccine.

Pfizer Inc. and BioNTech SE became the first of the leading vaccine developers to announce data from their Phase III trials, which began on July 27, 2020. 

So far, the trials have involved 43,538 volunteers. Initial trial data showed that the vaccine was 95% effective in preventing the coronavirus.

Pfizer and BioNTech estimate that they’ll produce 50 million vaccine doses by the end of 2020 and up to 1.3 billion doses in 2021. The vaccines will be distributed to multiple countries that have signed purchasing contracts, including the United States.

You will need two 0.3-milliliter doses of this vaccine with the second dose administered 21 days after the first dose. 

The primary drawback to the Pfizer vaccine is that it has to be stored and transported in temperatures of -70 degrees Celsius, which requires specialized fridges that many health care facilities don’t have access to. 

Once an undiluted vial of the vaccine (which includes about five doses) is thawed, it can be kept in the fridge for five days, but once the doses have been diluted, it’s only good for six hours.

However, Pfizer has been working with federal and state governments to determine the best way to transport and distribute the vaccines safely and effectively.

Pfizer is a leading United States-based pharmaceutical corporation and one of the largest in the world. It’s produced multiple popular medications, including Lipitor, Lyrica, Zithromax, and Viagra among many others. It also developed the Prevnar 13 pneumococcal conjugate vaccine.

BioNTech is a German-based biotechnology company that works primarily on developing immunotherapy-based treatments for many diseases, including cancer. In particular, it develops mRNA-based treatments to use in cancer therapies.


Vaccine type: mRNA

Efficiency in preventing the coronavirus: 94.1% effective

How many doses: 2 equal 100-microgram doses with the second dose a month later after the first dose

Side effects: Flu-like symptoms, including fever, headaches, muscle pain, or reactions at the injection site

Moderna, Inc. was the second to announce preliminary results of its Phase III trial, which completed enrollment on October 22, 2020, and involved 30,000 participants

Data from the Phase III trial showed the mRNA vaccine candidate, called mRNA-1273, was 94.1% effective in preventing the coronavirus. 

The company estimates that it will have about 20 million doses of its vaccine by the end of 2020 for the United States with another 500 million to 1 billion doses available globally in 2021. 

As with the Pfizer vaccine, you’ll need two doses with the second dose given four weeks later. 

Modern’s vaccine is stored at -20 degrees Celsius for up to six months, but it can be kept at normal fridge temperatures (2 to 8 degrees Celsius) for 30 days and at room temperature for 12 hours. Unlike the Pfizer vaccine, it doesn’t have to be diluted before administration. 

Moderna is a United States-based biotechnology company that focuses entirely on developing mRNA-based medications and vaccines.

AstraZeneca and Oxford

Vaccine type: Live virus

Efficiency in preventing the coronavirus: an average of 70% efficacy

How many doses: 2 doses, with the second dose a month after the first, but ongoing trials are still determining how large the doses will be

Side effects: Flu-like symptoms, including fever, headaches, muscle pain, or reactions at the injection site

AstraZeneca and the University of Oxford co-invented the third vaccine candidate to report Phase III efficacy preliminary results. The trials that provided the data reported on involved 23,000 participants, but many other trials are ongoing or in the works.

Unlike the Pfizer and Moderna vaccines, the AstraZeneca vaccine, named AZD1222, is not mRNA based. The vaccine uses a live virus to trigger the body’s immune response.

The virus used causes colds in chimpanzees and is harmless to humans. It has the same genetic code for the protein that the coronavirus has, which in theory should effectively train the immune system to respond correctly and develop immunity to the coronavirus. 

The AstraZeneca vaccine is also a two-dose vaccine with the second dose given a month after the first, but due to a misstep in one of its trials, some participants got only a half dose for the first dose and a full dose for the second. Data from that particular trial showed that the vaccine was 90% efficient in preventing coronavirus.

However, in the rest of the trials where participants received the normal full dose for both their first and second vaccinations, data shows the vaccine as around 62% effective. With the 90% and 62% results, that leaves a 70% average. Due to that discrepancy, AstraZeneca plans to run more trials to determine the best dosage.

The company plans to manufacture up to 3 billion doses of its vaccine in 2021. 

Unlike the other two leading vaccines, the AstraZeneca vaccine can be stored at regular refrigeration temperatures for up to 6 months, making it the most easily accessible and transportable vaccine option. 

AstraZeneca is a British-Swedish pharmaceutical and biopharmaceutical company that’s located in England. The company has produced many medications and treatments for a wide variety of conditions and has also developed and produced an intranasal flu vaccine. 

The University of Oxford runs a company called Vaccitech Limited, which is a spin-off biotechnology company that works on developing vaccines and immunotherapies for several diseases, including cancer and hepatitis B. 

After Approval

As COVID-19 vaccines are still new, there isn’t any data available yet on how long immunity will last. Each company and regulatory body will continue Phase IV trials for at least two years after trial participants received their second dose to continue monitoring the safety and efficiency of the vaccines.

Additionally, those who receive a COVID-19 vaccine may suffer from flu-like side effects that some trial participants reported. This is a result of the body’s immune system and immune response, and side effects like these are not uncommon for many vaccines.

While there’s still much we don’t know about COVID-19 or the vaccines, we do know enough to determine that the benefits outweigh the risks of the vaccines. The vaccines are backed by solid science and, although the process has been expedited, they have gone through a thorough review process before approval.