Background information: testing of vaccines
Everybody is familiar with vaccines. What is little-known, though, ist that there are two different kinds of vaccines: ones that are used against an infectious agent (bacteria or viruses such as measles) or there are cases where it is not the germ itself which causes disease but its toxin. The pathogenic agent which causes tetanus is an example: the bacterium Clostridium tetani produces the tetanus toxin, and the toxin is causing the symptoms.
What does this mean in practice? A vaccine against tetanus is not directed against the bacterium, but against its toxin. The same applies to diphteria vaccine – tetanus and diphteria are amongst the most commonly applied vaccines worldwide.
Therefore the toxin has to be produced and then rendered harmless (inactivated, the inactivated toxin is called toxoid and the resulting vaccine toxoid vaccine) in such a way that in can be administered to a recipient without causing symptoms. At the same time, the inactivation must not change the structure of the toxin too much, or the effect of the vaccination will be lost; the toxoid must “look right” to the organism, otherwise there will not be an effective immune defense.
In practice this means that toxoid vaccines have to be tested twice:
1) for their ability to evoke an immune reaction (potency test)
2) for their safety/ residual toxin activity after inactivation (quality test)
The former tests are now in vitro methods (recommended for tetanus since 2007 in Europe) although the animal testing is still not eliminated from regulations. The safety/quality testing is still a lot more problematic. Since a residual toxin activity can cause dangerous side effects, manufacturers and regulatory authorities are particularly concerned. The European Pharmacopoeia states that these vaccines have to be tested in the animal before they can be released. For this purpose, the vaccine is given to the experimental animals which are then observed for symptoms. In Germany alone, this concerns about 3000 animals each year; in this case guinea pigs.
In order to guarantee safety, and for monitoring the production procedures, this is not only done for the end product, but additionally several times during manufacturing. And: in the case of toxoid vaccines this has do be done for every new production unit separately. The reason for this is that the teanus toxin is produced by bacteria, and this step is highly variable and hard to control. Inactivation is done with formaldehyde, which changes the toxin’s structure and results in a heterogenous product. For these reasons, in vitro methods have not had their breakthrough in routine testing – this is about biological activity in living organisms.
For these test procedures there is an urgent need for animal-free methods. For tetanus vaccine, such a method is at the moment developed at the Paul-Ehrlich Institute in Langen, Germany – with the help of Animalfree Research.
For further reading:
Report and recommendations of ECVAM Workshop 61 (pdf)
