< Vaccines

Why is the vaccine already licensed when the clinical trials are not finished?

Text updated on 2021-02-17

There are four phases in the development of a vaccine (see the question How do you know if a vaccine is safe and protects against COVID-19 ?). Phases 1 and 2 have been completed for the vaccines Moderna, Pfizer, AstraZeneca. Phase 3 trials are still ongoing but have already provided sufficient information to give a clear picture of their efficacy and adverse effects. The presentation of these Phase 3 results to the scientific community has enabled the health authorities of various European and American countries (see question Who decides whether a vaccine can be marketed and how it should be administered?) to authorize the marketing of these three vaccines (two in the United States, with AstraZeneca's vaccine not yet authorized in February 2021). The vaccines can then be marketed and used on a large scale. 

This is when Phase 4 begins, which is not an experimental phase strictly speaking, but a pharmacovigilance phase, after a vaccine is marketed. This Phase 4 makes it possible to monitor the long-term effects of the vaccine and to answer questions such as how long the immune system remains protected after vaccination, the proportion of healthy carriers (can vaccinated people who have developed antibodies against the coronavirus still be infected and transmit the disease), etc. This Phase 4 is not an experimental phase as such, but a pharmacovigilance phase, after a vaccine is marketed.

This is the normal development process for any vaccine or drug.

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The European system for the regulation of medicinal products.

European Medicines Agency.

The WMA and the drug pathway.


European and French procedures for placing vaccines on the market.

General information on vaccinations.

On December 21, 2020, the European Medicines Agency and then the European Commission gave the go-ahead for Pfizer and BioNTech's vaccine against the COVID-19 disease.

EMA approval of the first vaccine against COVID-19.

The different stages of vaccine development.

The development of a vaccine.

Precise explanations of the development process for COVID-19 vaccines.

The COVID-19 Vaccine Communication Handbook. Last accessed February 2, 2021.

Current status of vaccines against COVID-19. World Health Organization publication updated twice a week.

WHO (2021) The COVID-19 candidate vaccine landscape.

In the case of Pfizer's vaccine, the administration of this vaccine throughout a whole country (Israel) will allow for the rapid generation of essential "real-life" information that will refine the data obtained in Phase 3 trials.

Real-world epidemiological evidence collaboration agreement. Last accessed February 9, 2021.

Further reading

Who decides whether a vaccine can be marketed and how it should be administered?

Were COVID-19 vaccines developed in a hurry?

Are RNA vaccines a miracle of science?

Are adverse vaccine reactions expected?