Question: how do you know that your vaccines are safe to test an animal with?

Ee Lyn Lim answered on 14 Jun 2013:

This is an interesting question. Giving someone a vaccine is like showing a fake shark’s fin to a bunch of people at the beach – it will frighten them a little, but won’t hurt them, and they’ll be well-armed with clubs and harpoons when a real shark does show up in the future. So a vaccine will only do its job if you show it to a proper working immune system, rather than to cells in a dish, which means it’s difficult to test it out before it’s given to animals.

What we CAN do is be a bit smarter when we’re making vaccines. Many vaccines are made of dead bacteria, or bits and pieces of bacteria or viruses, or maybe bacteria and viruses which are missing bits here and there. Scientists have done lots of work to learn how bacteria and viruses cause disease, so we know which bits we need to knock out to make a bug harmless. By carefully designing a vaccine, rather than just heating up a pot of bugs and hoping for the best (more or less what we did a few hundred years ago!), we can be more confident that our test animals won’t get really sick.

Of course, there’s also other factors to think about, like how much of a vaccine to give – too much and it might be deadly, too little and the animal might not be able to fight off a real infection. The best we can do here is really trial and error to find out what works best. But the important thing is that this process of trial and error will only be done once for each vaccine, or for any other drug for that matter, and the best way to carry out an experiment will be recorded so that it can be followed in the future.