How Do We Know the Vaccines are Safe and Effective?

Vaccines and new drugs go through a lot of testing before they are approved or authorized for public use.

Worried the vaccines aren't safe? Think they were made just too quickly to work? Let's look at the data to understand how we know the Pfizer and Moderna vaccines for COVID-19 are safe and effective.

On this page:


WHAT ARE CLINICAL TRIALS?

covid, questions, answers, vaccine, mrnaUnlike vitamins, minerals, and herbal supplements we buy over the counter, vaccines and medications go through strict testing and review to find out if and how they work.

  • Clinical trials test the medication or vaccine by giving it to human volunteers.
  • During these trials, volunteers are either given the medicine or vaccine OR are given a placebo.
    • A placebo is generally made from something harmless like salt water or sugar.

HOW STRICT ARE CLINICAL TRIALS?covid, questions, answers, vaccine, mrna

  • The testing must meet the Food and Drug Administration's (FDA) strict definitions, guidelines, phases, and quality assurance processes.
  • All FDA-authorized or approved vaccines are tested through THREE CLINICAL TRIAL PHASES:

The COVID-19 vaccine trials have been MUCH larger. The virus has caused so much death and illness that the vaccines have been given a lot of priority and support. 

  • Pfizer and Moderna tested their vaccines using what is called "Randomized Clinical Trials." This means some of the volunteers were given the real vaccine and some were given a placebo, or fake vaccine.
  • These Randomized Clinical Trials were "double-blind." That means the investigators (the ones giving the volunteers the vaccine and recording the results) and the volunteers did not know WHO was getting the real vaccine and who was getting the placebo. Only a group of researchers called the "Study Team" were given the information about who was in the placebo group and who was in the vaccine group.
  • All volunteers signed up for a two-year study period; they will continue to be monitored for side-effects and results during these Randomized Clinical Trials until 2022.

-Back to Top- 


WHAT THE CLINICAL TRIALS SHOW ABOUT HOW WELL THE VACCINES WORK 

Pfizer Clinical Trials

covid, questions, answers, vaccine, mrna44,000 people world-wide volunteered for the Pfizer clinical trials.

covid, questions, answers, vaccine, mrnaWorldwide, Pfizer had 150 locations for its testing. That number is important because it means:

  • MORE TESTING could be done at the same time than if they tested at one or two locations.
  • MORE PEOPLE were able to be a part of the testing, and
  • MORE RESULTS were able to be analyzed and shared.

covid, questions, answers, vaccine, mrnaOf the 44,000 people in the clinical trials ONLY 170 people got COVID-19. That's about 0.4% of the people in the trials.

covid, questions, answers, vaccine, mrnaOf the 170 who got COVID-19, ONLY 8 were in the vaccine group.

That means only 8 of all those in the vaccine group (22,000 people) caught COVID while on the vaccine.

This calculates to mean the Pfizer vaccine is greater than 95% effective at preventing COVID-19 infection.

-Back to Top- 

Moderna Clinical Trials

covid, questions, answers, vaccine, mrna30,000 people world-wide volunteered for the Moderna vaccine randomized clinical trials.

covid, questions, answers, vaccine, mrnaWorldwide, Moderna had 100 locations for its testing. That number is important because it means:

- MORE TESTING could be done at the same time than if they tested at one or two locations.
- MORE PEOPLE were able to be a part of the testing, and
- MORE RESULTS were able to be analyzed and shared.

covid, questions, answers, vaccine, mrnaOf the 30,000 people in the clinical trials, ONLY 95 got COVID-19.

That's about 0.3% of the people in the trials.

covid, questions, answers, vaccine, mrnaOf the 95 who got COVID-19, ONLY 5 were in the vaccine group.

That means only 5 of all those in the vaccine group (15,000 people) caught COVID while on the vaccine.

This calculates to mean the Moderna vaccine is greater than 94% effective at preventing COVID-19 infection.

-Back to Top- 

About the Clinical Trial Volunteers

The Pfizer Volunteers

covid, questions, answers, vaccine, mrnaOf the 44,000 volunteers in the Pfizer Clinical Trials:

- 58% of the volunteers are white
- 26% are Hispanic/Latinx
- 10% are Black
- 5% are Asian
- 1% are Native American

covid, questions, answers, vaccine, mrna Of the 44,000 volunteers in the Pfizer Clinical Trials:

Birth sex -
 - 50% of the volunteers' birth sex is male
 - 50% of the volunteers' birth sex is female

Ages - 
 - 3% of the volunteers are ages 12-17 (these are new to the trials as of Phase 3)
 - 56% are ages 15-55 years old
 - 40% are 56 or over

covid, questions, answers, vaccine, mrnaOf all of the Pfizer Clinical Trial volunteers:


- 25% have hypertension (high blood pressure)
- 25% are obese (a Body Mass Index of 30 or more)
- 8% are diabetic
- 8% have chronic pulmonary disease, and
- About 1% have liver disease

-Back to Top- 

The Moderna Volunteers

covid, questions, answers, vaccine, mrnaOf the 30,000 Moderna Clinical Trial Volunteers:


- 63% of the volunteers are white
- 20% are Hispanic/Latinx
- 10% are Black
- 4% are Asian
- 3% are Other Races/Ethnicities

covid, questions, answers, vaccine, mrnaOf the 30,000 volunteers in the Moderna Clinical Trials:

Birth sex -
 - 53% of the volunteers' birth sex is male
 - 47% of the volunteers' birth sex is female

Ages - 
 - 5% of the volunteers are 18-24 years old
 - 29% are 25-44 years old
 - 39% are 45-64 years old
 - 25% are 65 or over

covid, questions, answers, vaccine, mrnaMore than 8,000 of the Moderna Clinical Trial volunteers live with serious chronic health conditions. Of these greater than 8,000 individuals:


 - 19% have significant cardiac disease
 - 25% are severely obese (a Body Mass Index of 40 or more)
 - 36% are diabetic
 - 18% have chronic lung disease, and
 - 2% have liver disease

-Back to Top- 

About the Vaccines' Side Effects

Every medication - from a vaccine to aspirin to a multivitamin - can have side effects. The side effects are important to know. 

Why do we get side effects when we get a vaccine? Your immune system is learning how to fight a virus. This means its working harder and may cause some side effects because of that. Neither vaccine from Pfizer or Moderna contain ANY virus - there is no chance of getting COVID-19 from the vaccine.

Pfizer

Most common side effects - which could last a couple days and were more noticeable after the second dose of the vaccine - include:

  • pain at the injection site,
  • tiredness,
  • headache,
  • muscle pain,
  • chills,
  • joint pain, and
  • fever.

Moderna

Most common side effects - which could last a couple days and were more noticeable after the second dose of the vaccine - include:

  • pain at the injection site,
  • tiredness,
  • headache,
  • muscle pain,
  • chills,
  • joint pain,
  • swollen lymph nodes in the same arm as the injection,
  • nausea and vomiting, and
  • fever.

-Back to Top- 

Next...How Could They Be Made Quickly and Still Be Safe?

Back....COVID-19 Vaccine Mainpage