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How Thorough Were the COVID-19 Vaccine Trials?

by Audrey Stevenson, PhD, MPH, MSN, FNP-BC

Recent surveys show that some top reasons people have hesitancy about receiving the vaccine is because A: They believe the trials were rushed and B: They would rather wait until others receive it before they make a decision. “You go before I go.” We get it. So, first let’s talk about the 118,000+ trial participants who did just that.

Let’s start with Pfizer.

For its vaccine, 44,000+ volunteers participated. Half received the vaccine, and the other half were given a placebo and all were told to go about their lives. During the trials, 162 of the estimated 22,000 placebo recipients contracted the coronavirus, while only 8 of the other 22,000 vaccine recipients tested positive for COVID-19. Of the 162 infected, 9 became severely ill with symptoms, while only 1 of the 8 vaccine recipients did. 1 in 22,000 vs 8 in 22,000. This led to the results that the Pfizer vaccine was found to be 95% effective at reducing disease and life-threatening symptoms. Think about those odds knowing there are 7.6 billion people on this planet, and you’re one of them.

Details: Requires 2 shots with 21 days in between receiving them, followed by a 14-day period after the second shot to reach full immunity.

Next up: Moderna.

For its trials, 30,000 participants were also submitted to the 1:1 ratio testing. Of the placebo group, 196 contracted COVID-19 with 30 cases being severe. Only 11 contracted the virus in the vaccine group with 0 showing severe symptoms. Both of these trials included participants ranging in ages from 18-71+ and from diverse communities including Hispanic, LatinX, Black or African American, Asian American, Multiracial, and Caucasian. Again, these numbers indicated a high 94.1% efficacy rate in preventing disease and hospital-grade symptoms or death.

Details: Requires 2 shots with 28 days in between receiving them, followed by a 14-day period after the second shot to reach full immunity.

The latest from Johnson & Johnson.

With J&J’s trials, it too conducted ratio testing for 43,700+ participants of various age groups and ethnicities. What’s different is, 41% of the participants had pre-existing conditions such as obesity, type 2 diabetes, hypertension, HIV, and other immune compromises. This is important because COVID-19 symptoms can be worse for people who have these at-risk conditions. Another difference with Johnson & Johnson is that unlike Pfizer and Moderna vaccines that have to be kept at extremely low temperatures and require 2 inoculations for effectiveness, J&J only requires 1 dose and can be stored safely at more regulated refrigeration for up to 3 months. As for the results, the vaccine provided 66% effectiveness at preventing moderate to severe symptoms, 28 days after the vaccination, but demonstrated 85% protection against hospitalization and death after day 28.

Details: 1 vaccination with full efficacy after 28 days.

As for the trials being “rushed”…

Typical vaccine developments and trials in a non-pandemic world require 3 main things: Resources, money, and approvals. Normally vaccines can take years to develop because they often run low on the first and second or can get tied up in long lines waiting for approvals from Food and Drug Administrations and similar government agencies who have other vaccines and drugs in the queue being reviewed for approval. When the pandemic hit, the world put everything else on hold, scientists came together to work on this sole solution, and governments, pharmaceutical companies, private donors, and citizens came together to make sure funding was not an issue. So, with these vaccines being prioritized and all-hands-on deck with unlimited money and resources, they were able to be developed faster, but no steps were skipped. They were merely streamlined.

As of February 12th, 2021: 46,390,270 people have taken the vaccine in the United States.


This site provides helpful facts from Utah’s top doctors and scientists, and information to help you schedule your vaccine appointment.

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