What are the challenges in developing new vaccines?

Vaccines have a major role to play in public health. However, despite decades of vaccine development there is currently only licensed vaccines for 26 infectious diseases.

These are listed in the table below:

Table adapted from WHO

Why vaccine development is difficult

Vaccine development is expensive and time consuming. New vaccines are initially tested in animal studies and only if they show promising results do studies or clinical trials begin in humans.

Clinical trials move through three phases, each with increasing numbers of participants. At each stage if a vaccine is unsafe, or shown not to work, then development is halted.

Image sourced from Centers for Disease Control and Prevention. A text version of the above image is available as a PDF.

Case study: vaccine for Plasmodium falciparum malaria

The pharmaceutical company GSK has spent more than 30 years developing its vaccine RTS,S (Mosquirix) against the parasitic infection Plasmodium falciparum, which causes malaria.

Currently this vaccine is undergoing assessment in phase 4 studies in Africa to provide further data on vaccine safety and efficacy. The illustration below highlights the decades spent developing this vaccine, the cost of which is estimated to be more than $800 million by the completion of Phase 4 trials.

Click to enlarge

Image sourced from Kaslow, D. and Biernaux, S., 2015. This is available as a PDF.