Clinical Trials

We study dozens of investigational vaccines each year, with thousands of Finnish volunteers participating annually.

Before a study begins, researchers from pharmaceutical companies, universities, biotech firms, and other medical institutions gather information on the disease targeted by the vaccine — its causes, prevalence, and severity. At the same time, an investigational vaccine is developed to prevent the disease or its complications. The preclinical phase (Phase 0) takes place in the laboratory, where the new vaccine is analysed chemically and may also be tested in cell cultures. Its effects are further assessed in animal models. This stage can last several years.

Clinical vaccine trials in various phases of development:

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Phase 1 – Studying adult volunteers

This first human trial phase focuses primarily on evaluating the safety of the vaccine. Participants keep a record of any symptoms that may appear after vaccination, and researchers monitor how their immune systems respond. Because the vaccine has not previously been tested in humans, only a small group (dozens) of healthy volunteers are involved.

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Phase 2 – Studying the target population

This phase involves a slightly larger group of volunteers, including individuals for whom the vaccine is intended — possibly including children. The study aims to determine the optimal dosage and schedule to achieve the best immune response with the fewest side effects. Participants are typically randomized and blinded into two groups: one receiving the investigational vaccine, the other a placebo or an already approved vaccine. Side effects and immune responses are tracked for weeks or months.

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Phase 3 – Large-scale efficacy trials

These trials can involve tens of thousands of volunteers from the vaccine’s target group, again divided into two groups as in Phase 2. The dose and schedule are chosen based on Phase 2 results. The main goal is to demonstrate the vaccine’s effectiveness by comparing disease incidence between the two groups. Side effects are also monitored and compared. Since diseases may take time to develop, follow-up may last months or even years.

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Phase 4 – Post-approval studies

After regulatory approval, further study is necessary because rare side effects may only become visible once the vaccine is widely distributed. This phase also monitors the vaccine’s long-term impact and how the incidence of the disease changes in the general population after vaccination begins. Finland’s extensive national registers and databases provide comprehensive, real-time health data that can be used for this purpose.

Go to open studies