English | Spanish

There has been a lot of public conversation about how quickly the COVID-19 vaccines were developed. While the vaccines were developed very fast, it’s important to know that this process was also comprehensive. Both the safety and effectiveness of the vaccines were tested thoroughly before being approved for Emergency Use Authorization. These vaccines are held to the same safety standards as other vaccines that are available, such as the flu vaccine.

Before the U.S. Food and Drug Administration (FDA) grants Emergency Use Authorization, the safety and effectiveness of the vaccines were reviewed by panels of independent experts retained by the drug companies, FDA scientific staff, and an independent panel of experts convened by the FDA. After treatment of tens of thousands of volunteers in the clinical trials, there were no reported safety concerns for the Pfizer, Moderna and Johnson & Johnson vaccines.

On August 23, 2021, the Pfizer vaccine received full FDA approval for the prevention of COVID-19 in people ages 16 and older. It continues to be available under emergency use authorization for children ages 12 through 15.

On April 13, 2021, the FDA paused the use of the Johnson & Johnson vaccine out of an abundance of caution to review data involving 6 U.S. cases of blood clots after receiving the vaccine. On April 25, the CDC and FDA announced to resume the use of the Johnson & Johnson COVID vaccine. A review of the data showed that the potential benefits outweigh its known and potential risks. The CDC says that women younger than age 50 should be aware of the rare but increased risk of thrombocytopenia syndrome (TTS) following the Johnson & Johnson vaccine, and that there are other vaccine options available.

While the Pfizer and Moderna vaccines are the first mRNA vaccines ever developed, the technology behind them has been researched and under development long before the COVID-19 pandemic. Years of advanced research on viruses similar to SARS-CoV-2 (the virus that causes COVID-19) also paved the way for quick development of these new vaccines. The Johnson & Johnson vaccine uses a technology that has been used in many other vaccines before.

In addition, due to the overwhelming impact of COVID-19 on the worldwide population, various industries worked to quicken their processes involved in vaccine development and production. This made them available sooner than other vaccines in the past. These expedited processes included:

  • Securing larger funding in order to run multiple trials at once
  • Moving through governmental regulations more quickly than usual
  • Manufacturing the vaccines more quickly than others in the past

Vaccine Development

The FDA is the regulatory authority that oversees vaccine development and approval in the United States. Ensuring the safety and effectiveness of newly developed vaccines is one of the FDA’s top priorities.

The FDA’s Center for Biologics Evaluation and Research (CBER) ensures that the FDA’s rigorous scientific and regulatory processes are followed by vaccine developers. The COVID-19 vaccines had to follow these protocols in order to receive Emergency Use Authorization in the United States.

The steps of development and approval for the first COVID-19 vaccines were:

Preclinical Studies: During this phase of the development process, a company’s team of researchers performs laboratory research and testing in animals to obtain information about how the vaccine works and if it’s likely to be safe and work well in humans..

New Drug Application: Before studies of the vaccine can begin in humans, the vaccine developers compile the results of their laboratory and other preclinical testing and submit these to the FDA in the form of an Investigational New Drug application (IND). The FDA evaluation includes an assessment of the preclinical data and a determination of whether these tests were conducted according to Good Laboratory Practices. The FDA also conducts an assessment of the product, its quality and safety, and the technology to manufacture it to determine whether it is safe to test the vaccine in people.

Phase I Clinical Trials: Once the FDA has approved the IND, the clinical trial process can begin. Phase I trials have an emphasis on safety and generally include 20–100 volunteers who haven’t been exposed to the disease being studied (and who are generally healthy). These studies are used to determine whether there are adverse reactions with increasing doses of the vaccine and, if possible, gain early information about how well the vaccine works.

Phase II Clinical Trials: In Phase II trials, various dosages are tested on 100’s of people with varying health statuses and from different demographic groups. These studies provide additional safety information on common short-term side effects and risks, examine the relationship between the dose administered and immune response, and provide initial information regarding the effectiveness of the vaccine in its ability to generate an immune response in recipients.

Phase III Clinical Trials: In Phase III trials, the vaccine is generally administered to thousands of people and the study generates critical information on effectiveness and additional important safety data. This phase includes determining additional information about immune response and compares those who receive the vaccine to those who receive a control, such as a placebo. These studies also provide information about the vaccine’s safety, including the identification of less common side effects.

Data Submission to the FDA: By submitting this data, the vaccine developer seeks permission to distribute and market a vaccine for use in the United States. The FDA evaluates the data to determine whether the safety and effectiveness of the vaccine has been demonstrated and whether the manufacturing and facility information assure product quality and consistency. After its evaluation, the FDA decides whether to approve/license the vaccine for use in the United States.

Emergency Use Authorization: In December 2020, the FDA granted both the Pfizer/BioNTech and Moderna vaccines Emergency Use Authorization (EUA). This made these vaccines immediately available in the United States while the FDA continues to review data prior to official approval. In order for vaccines to be approved for emergency use, there must be data that strongly indicates it is both safe and effective. The Johnson & Johnson / Janssen vaccine was granted an EUA in February 2021.

Full FDA Approval: On August 23, 2021, the FDA approved the Pfizer vaccine as the first COVID-19 vaccine to prevent COVID in people 16 years of age and older.

Page last updated August 30, 2021.