Journey of a Vaccine

Learn about the four phases of clinical research, what questions researchers try to answer in each, and how a vaccine is developed, approved, and manufactured.

Understanding Vaccine Studies

What are the differences between the vaccines that are available? 
Vaccine syringe

These vaccines have received emergency use authorization from the FDA:   

  • Pfizer, Inc., and BioNTech BNT162b2: On December 11, 2020, the FDA authorized emergency use of the first COVID-19 vaccine in the United States for people 16 years and older. View the infographic to see what’s in the Pfizer COVID-19 vaccine.  

  • Janssen Pharmaceutical Companies of Johnson & Johnson: On February 27, 2021, the FDA authorized emergency use of this single-shot vaccine for people 18 years and older. Developed with support from NIH funding, this vaccine does not require special refrigeration.  Women younger than 50 years old should be aware of the rare risk of blood clots after vaccination.

How do I know the vaccines are safe and effective?
Vaccine vial and syringe being held

Vaccines have very high safety standards, and the vaccines available to prevent COVID-19 are no exception. COVID-19 vaccines are authorized  by the FDA for use only if they have proven safe and effective in a large group of people. 

Although the search for and development of the COVID-19 vaccines seemed to move fast, decades of existing research on coronaviruses gave the scientific community a head start on understanding COVID-19 and developing a vaccine. Researchers, the federal government, and drug companies came together like never before to cooperate and share resources, making the testing process more efficient. 

Also, the FDA has made the safety standards and approval process even tougher than usual. The FDA set minimum requirements for the effectiveness of products to approve only those vaccines that could offer immunity to the majority of the population.   

Find more questions and answers about a COVID-19 vaccine 

How long will my immunity last after I get the vaccine? 
Vaccine being administered to individual

Researchers don’t know for sure how long immunity produced by vaccination lasts. You are considered fully protected two weeks after your second dose of the Moderna or Pfizer-BioNTech vaccine, or two weeks after the single-dose Johnson & Johnson’s Janssen vaccine.   

However, because we do not know how long the vaccine protects you, you should still take precautions to protect yourself and others by following current CDC guidelines: wearing masks in public, washing your hands often, and social distancing.   

Do the vaccines work against the virus variants? 
COVID molecule

We know that the COVID-19 vaccines available now are effective at preventing COVID-19. So far, studies suggest that these vaccines should also work against the variants that have emerged. Current data show that the antibodies are bodies make after vaccination may recognize and protect against the variants. This is being closely investigated, and more studies are underway.   

The rise of these variants is a reminder that as long as SARS-CoV-2 continues to spread, it has the potential to evolve into new variants. Viruses can’t mutate if they can’t replicate. The more people who get vaccinated, the harder it is for the virus to replicate. Widespread vaccination will help reduce the rise of additional variants. 

Read about NIH research to study the variants

When can children get a vaccine? 
Child wearing mask sits with a healthcare provider

Children and teens ages 12 years and older can now get the Pfizer vaccine. COVID-19 vaccines are not yet approved for use in people younger than 12 (Pfizer) or 18 (Moderna and Johnson & Johnson vaccines). However, clinical trials are now underway to test the safety and effectiveness of currently available vaccines in younger children. Experts hope children and adolescents will be approved to receive the vaccines by fall 2021.

Will I need a booster shot after being fully vaccinated against COVID-19?
Person signing up for treatment

NIH is researching whether people who have been fully vaccinated against COVID-19 will require additional shots for continued immunity. Current research aims to determine whether approved vaccines will grant immunity against emerging COVID-19 variants and if new vaccines will be needed.

Are vaccines still being researched? 
Researcher conducting study

Yes, new and ongoing studies on vaccines are underway. NIH institutes and centers, in partnership with private businesses, continue to study different types of vaccines as well as other ways to prevent COVID-19, such as monoclonal antibodies. None of the vaccines or other preventives contain whole or live SARS-CoV-2 virus. This means they can’t cause COVID-19.   

  • Vaccine studies: Some vaccine trials continue to enroll participants for the development of more vaccine options to help people build immunity to the virus. Other vaccine studies continue to follow people who have already had a vaccine to make sure we are collecting as much information as possible about how the vaccines work over a long period of time.   

  • Monoclonal antibody studies: A study called BLAZE-2 is testing if lab-made antibodies can prevent the SARS-CoV-2 virus from entering healthy cells. The antibodies cannot cause COVID-19. 

Learn more about current vaccine and antibody research 

Vaccine Resources

Antibodies can be effective at preventing COVID-19, especially for people w...

Vaccines testing through the different phases of clinical trials

Learn what to expect when you volunteer for a vaccine clinical trial.

Get the facts about COVID-19 vaccine studies.

Selected NIH-Published Vaccine Research

Mascola, J.R.,Graham, B.S., Fauci, A.S. SARS-COV-2 Viral variants—Tackling a moving target.JAMA DOI: 10.1001/jama.2021.2088 (2021).

Baden, L. R., El Sahly, H. M., Essink, B., Kotloff, K., Frey, S., Novak, R., . . . Zaks, T., on behalf of the COVE Study Group. Efficacy and safety of the mRNA-1273 SARS-CoV-2 vaccine. The New England Journal of Medicine, 384(5), 403–416. doi:10.1056/NEJMoa2035389 

Haynes, B. F., Corey, L., Fernandes, P., Gilbert, P. B., Hotez, P. J., Rao, S., . . . Arvin, A. (2020). Prospects for a safe COVID-19 vaccine. Science Translational Medicine, 12(568), eabe0948. doi:10.1126/scitranslmed.abe0948

Hewitt, J. A., Lutz, C., Florence, W. C., Pitt, M. L. M., Rao, S., Rappaport, J., & Haigwood, N. L.; ACTIV Preclinical Working Group. (2020). ACTIVating resources for the COVID-19 pandemic: In vivo models for vaccines and therapeutics. Cell Host and Microbe, 18(5), 646659. doi:10.1016/j.chom.2020.09.016

Deming, M. E., Michael, N. L., Robb, M., Cohen, M. S., & Neuzil, K. M. (2020). Accelerating development of SARS-CoV-2 vaccines the role for controlled human infection modelsNew England Journal of Medicine, 383, e63. doi:10.1056/NEJMp2020076

Collins, F. S., & Stoffels, P. (2020). Accelerating COVID-19 Therapeutic Interventions and Vaccines (ACTIV): An unprecedented partnership for unprecedented times. JAMA, 323(24), 24552457. doi:10.1001/jama.2020.8920

Corey, L., Mascola, J. R., Fauci, A. S., & Collins, F. S. (2020). A strategic approach to COVID-19 vaccine R&D. Science, 368(6494), 948950. doi:10.1126/science.abc5312