All medicines go through a series of development stages and tests before a manufacturer can apply for approval. This development includes laboratory testing, animal studies and, finally, studies in humans. The entire development process, from early laboratory research to a finished vaccine, can take up to 15 years (1, Swedish Medical Products Agency, 2021).
Unlike many other medicines, vaccines are given to healthy individuals, which means that only rare and mild side effects are considered acceptable. To reliably identify rare side effects (those affecting fewer than 1 in 1,000 people) or delayed side effects that may appear only after several years, long-term follow-up of large numbers of individuals is required. Drug development takes place in several stages (2, European Medicines Agency, EMA, 2025):
- Preclinical studies: The effects of new vaccines are first tested in laboratory settings and through animal studies.
- Phase 1 studies: The vaccine is tested in up to ten healthy volunteers to map side effects and assess whether sufficient antibody levels are produced.
- Phase 2 studies: A larger number of volunteers are included to further evaluate the most common short-term side effects, the immune response, and to determine the optimal dose.
- Phase 3 studies: Up to thousands of participants are studied to assess antibody levels (surrogate markers) or the vaccine’s protective effect, and to identify the most common side effects.
In clinical trials, a vaccine is almost always compared with an inactive vaccine or with another vaccine that protects against a different infection (1, Swedish Medical Products Agency, 2021).
Vaccines are biological medicines, meaning they are produced from living organisms and have a more complex manufacturing process than conventional chemically synthesised medicines. This complexity makes it more challenging to ensure quality, stability and safety (3, Swedish Medical Products Agency, 2020).
Once the studies have been completed, the vaccine is reviewed by regulatory authorities such as the FDA in the United States and the EMA in Europe before it can be approved – a process that can take several years. To speed up access to vaccines, there are alternatives to full approval (4, Swedish Medical Products Agency, 2023):
- Conditional approval: Granted when the benefits are considered to outweigh the risks despite limited data and reliance on surrogate markers.
- Approval under exceptional circumstances: When studies in humans are unethical or impractical, approval may be based on data from animal studies or individual patient cases.
- Biosimilars: A biological medicine considered equivalent to an already approved product may be authorised without full clinical trials (5, Swedish Medical Products Agency, 2022).
Phase 4 studies correspond to the period after the vaccine has entered the market and is in use. This phase can be seen as structured monitoring of effectiveness and safety when the vaccine is used in larger populations (1, Swedish Medical Products Agency, 2021).
Despite extensive testing serious side effects can occur (6, EMA, 2025). To manage the financial consequences of medicine-related injuries and potential compensation claims, Sweden and other countries have introduced compensation schemes. These programmes facilitate continued vaccine development and innovation by reducing the financial risks for companies (7, Pharmaceutical Insurance).
In summary, these programmes, processes and alternative development pathways make it possible to balance the demands for extensive, time-consuming safety studies with the need for rapid access to vaccines in critical situations.
Sources
- Testing and development, Swedish Medical Products Agency, 2021, https://www.lakemedelsverket.se/sv/behandling-och-forskrivning/vaccin/utveckling-av-vaccin/testning-och-utveckling
- Approval of vaccines in the EU, European Medicines Agency (EMA), 2025, https://vaccination-info.europa.eu/sv/om-vacciner/godkannande-av-vacciner-i-eu
- Biological medicines, Swedish Medical Products Agency, 2020,
https://www.lakemedelsverket.se/sv/tillstand-godkannande-och-kontroll/tillverkningstillstand/biologiska-lakemedel - Alternatives to full approval, Swedish Medical Products Agency, 2023, https://lakemedelsboken.se/generella-kapitel/godkannande-av-lakemedel/bedomning-av-effekt/alternativ-till-fullstandigt-godkannande/
- Biosimilars, Swedish Medical Products Agency, 2022, https://www.lakemedelsverket.se/sv/tillstand-godkannande-och-kontroll/tillverkningstillstand/biologiska-lakemedel/biosimilarer
- EudraVigilance – the European database of suspected adverse drug reactions, European Medicines Agency (EMA), 2025, https://www.adrreports.eu/sv/
- Questions and answers about the Pharmaceutical Insurance, Pharmaceutical Insurance (Sweden), https://lff.se/om-du-skadas-av-ett-lakemedel/fragor-och-svar/
