Vaccine Clinical Trials

Just like new medications and medical devices, new vaccines must go through clinical trials to prove they’re safe and effective.1 These long-term studies measure how well vaccines work at preventing infection and illness and ensure there are few side effects.

Clinical trials for vaccines can look a bit different compared to traditional clinical trials — they also tend to have different eligibility criteria that allow you to participate.

Keep reading this article if you’re interested in potentially joining a vaccine clinical trial or if you’d just like to learn more about what’s currently happening in research. It’s important to note that vaccine clinical trials and science are constantly changing, and this article captures just a fraction of ongoing research.

Vaccine Clinical Trials Process

Vaccines are licensed after they go through the three phases of clinical trials. However, since vaccines aren’t looking to treat a certain disease or condition, these trials are slightly different from traditional studies.1,2

Phase 1 Clinical Trials for Vaccines

Phase 1 studies involve a small group of healthy adult volunteers who are the first to try the vaccine. Investigators use these studies to determine whether a vaccine is safe, what the correct dosage is, and whether it triggers an immune response. The goal of a phase 1 trial is not to determine whether the vaccine is effective at preventing infection or illness.

Phase 2 Clinical Trials for Vaccines

Phase 2 studies involved hundreds of volunteers who are the same sex and age range as the intended recipients. Investigators will conduct multiple trials to recruit a diverse population of people with different backgrounds, races, and ages (within a range) to learn how the vaccine works in these groups.

The investigators will also likely recruit a group of volunteers who receive a placebo or “fake” dose to compare to the vaccinated group. This comparison can help determine whether any benefits are due to the vaccine or have happened by chance. Overall, the goals of phase 2 studies are to learn about how well the vaccine works and to observe what side effects occur.

In some closely monitored instances, the volunteers are exposed to the infection or toxin to assess effectiveness. Such trials are referred to as “challenge trials.”3

Phase 3 Clinical Trials for Vaccines

Phase 3 studies are expanded to thousands of volunteers to continue gathering data on a vaccine’s safety and efficacy. By recruiting even more participants, investigators can look for larger trends in how well a vaccine works and whether side effects seen in phase 2 continue to occur.

Often, phase 3 studies are conducted at multiple hospitals and sites around the country to include as much diversity as possible. It’s important to continue to recruit people of different ages, sexes, and races, as genetics and underlying health conditions can affect vaccine efficacy.

For nearly all phase 2 and 3 studies, investigators and participants are “blinded” — this means that neither group knows who received the vaccine and who received a placebo. Blinding ensures there isn’t any bias and investigators aren’t influenced by knowing the assignments.

The U.S. Food and Drug Administration (FDA) also reviews how companies plan on manufacturing their vaccines. They conduct safety inspections to ensure the vaccine is made safely and reliably.2

Results of Vaccine Clinical Trials and Licensing

After the investigators gather all of the results and data, they submit their findings to the FDA for final approval and licensing. The FDA takes into account any preclinical testing performed on cells and animals and clinical trial results. The studies must show that the vaccine improves a person’s immunity, is safe, and causes few to no unwanted side effects.2

Vaccines are measured by how effective they are, or what’s known as their efficacy. Investigators measure how many people who were vaccinated became sick versus how many of those who received the placebo became sick. The efficacy is given as a percentage — if a vaccine has a proven efficacy of 70 percent, this means that people who received the vaccine are at a 70 percent lower risk of getting sick compared to those who didn’t.4

From start to finish, it can take anywhere from 5 to 10 years to develop a vaccine, perform clinical trials, and secure licensing. This process can be expedited depending on the need for a new vaccine. In the case of COVID-19, clinical trials were safely expedited to license vaccines to combat the global pandemic.5

Trends in Vaccine Clinical Trials

Find Clinical Trials Near Me

Interested in clinical trials? Simply search by postal code and type of condition to see what’s going on in your area.


New vaccines are being developed every year against bacteria and viruses that pose a threat to our health. Investigators are also making discoveries in using vaccines to treat certain types of cancer. By training our immune systems to fight foreign invaders or activating them against cancer cells, we can better prevent infections and fight diseases.

New Vaccinations Against Pathogens

The FDA has licensed nearly 100 vaccines for preventing infection by harmful viruses and against toxins made by bacteria. Many of these vaccines are routine throughout childhood, while others may be required when traveling to certain areas of the world.6

However, there’s still a need to create vaccines against other infections, including:7,8

  • Human immunodeficiency virus (HIV) — A virus that destroys immune cells, eventually leading to acquired immunodeficiency syndrome (AIDS)
  • Malaria — An infection caused by Plasmodium parasites carried by mosquitos
  • Shigella — Bacteria responsible for causing dysentery (an intestinal infection causing bloody diarrhea)
  • Epstein-Barr virus (EBV) — A virus that infects over 90 percent of people at some point in their lives, particularly in childhood; it causes mononucleosis and may be involved in certain types of cancer and multiple sclerosis (MS)

Ongoing clinical trials are in various stages investigating vaccines to protect against these infections. Doctors and researchers hope that successful vaccines will prevent several health complications.

Cancer Vaccinations

The concept of vaccinations against cancer is becoming more popular as we learn more about how the immune system can be activated to fight it. There are currently a handful of licensed cancer vaccines that help train the immune system to recognize certain proteins (antigens) made by cancer cells. As a result, the immune system attacks tumor cells, helping to treat cancer that isn’t responding to traditional treatments.9

There are several vaccines currently in clinical trials for:10

  • Pancreatic cancer
  • Breast cancer
  • Certain types of brain cancer, including gliomas
  • Colorectal cancer
  • Blood cancers, including leukemias and myelomas
  • Lung cancer

Investigators are looking into using vaccines alongside other approved cancer therapies to improve responses.

COVID-19 Vaccine Monitoring

Doctors and researchers continue to monitor vaccines after they’re licensed to ensure they’re still safe and effective for the general public. Post-marketing surveillance trials — also known as phase 4 clinical trials — are an important part of monitoring vaccines.11,12

The FDA has licensed several COVID-19 vaccines, which have been proven both safe and effective for the general public. Now, investigators continue to monitor their use. For example, some studies are investigating unwanted side effects from COVID-19 vaccines.

Other observational clinical trials are used to learn more about why certain populations are less likely to get vaccinated or to find ways to predict who may respond better to a vaccine compared to others. All of the information gathered in these clinical trials helps doctors and researchers build better vaccines in the future.

Participating in a Vaccine Clinical Trial

If you’d like to participate in a vaccine clinical trial, it’s important to take several factors into consideration. According to the National Institute of Allergy and Infectious Diseases (NIAID), the average vaccine study takes around one year.13 During this time, you may have several clinic visits, and you’ll receive one or more doses of a vaccine or placebo. Joining a clinical trial can be a significant time commitment — the clinical trial staff will go over the schedule and number of visits required for a particular study. You will probably also have several blood tests to measure any antibodies you produce in response to the vaccine.

There’s also the chance that you may have an unwanted or adverse side effect, or you may see no benefit from the vaccine. Clinical trials aren’t guaranteed to offer any solutions or immunity from the infection or disease being studied. You’re volunteering your time and effort to the advancement of science and medicine, and any benefits are an added bonus.

Eligibility Criteria for Vaccine Clinical Trials

Once you’ve decided you’d like to join a vaccine clinical trial, you’ll need to find one you qualify for. Clinical trial investigators post their eligibility criteria or a list of requirements to meet to participate in a study. The criteria are selected to keep participants safe during a clinical trial and to ensure the data are as accurate as possible.

Inclusion criteria are a set of requirements you must meet to participate. Many vaccine clinical trials will require you to be a certain age so you’re able to give your informed consent. You’ll also have to be in generally good health and be able to attend all required visits.

Exclusion criteria are circumstances that prevent you from participating in a clinical trial. Vaccine clinical trials tend to limit who can join for the sake of safety. Common exclusion criteria for vaccine studies include being pregnant or breastfeeding, having cancer or a serious chronic illness, taking immunosuppressive medications that dampen your immune system (such as chemotherapy for cancer), or having a history of seizures.

Joining a Vaccine Clinical Trial

Joining a clinical trial can be a rewarding experience. It’s important that you choose to join a clinical trial for your own reasons, taking your best interests into account. Be sure to talk to your family, friends, and doctors about joining a study — they can help you weigh the benefits and risks.