Hi there MariaBN6. I'm flattered that you think I sound like a medical professional, but I am not. As a result you should feel free to distrust anything I say, and take the opportunity to verify my statements for yourself.
For any drug to be administered or sold in the UK (or most developed countries) it must go through a series of clinical trials. The most common are phase 1, 2 and 3 trials. In the phase 1 trials a small group of healthy volunteers are given the drug, and the scientist test to see if it is dangerous. If it is not then the phase 2 trial starts. The drug is given to about 300 volunteers to test for the safety and efficacy of the drug. If the drug passes this stage (most don't) it goes on to a phase three trial. In this trial the drug is tested against either the current best drug (its rival) or a placebo if no similar drug exitst. This is a double blind trial (neither the doctor nor patient know which person receives the drug) performed on around 3000 people. This trial tests for the efficacy and safety of the drug. Normally several of these phase 3 trials are performed.
The results of the trials are then analysed by a regulatory body (the MHRA in the UK, the FDA in the US) and the drug, if it can be shown to be effective and safe, is given a license to be sold. This same body oversees the trials, ensuring they are ethical and effective.
After the drug is licensed the testing does not stop. Doctors are encouraged to, and do, report any adverse reactions, regardless of how minor, to the yellow card scheme. This scheme, run by the MHRA, is used to monitor trends in drug reactions to identify any problems not detected in the clinical trials. This may seem rather reckless, using the public as a way of testing drugs, but it isn't. No drug is 'perfectly safe', but the benefits of the drug outweighs the risks. The same is true of vaccines. No vaccine is 'perfectly safe', but the diseases that they prevent are more than enough justification to use them. If we avoided licensing drugs until they had been through thousands of trials we would have much fewer drugs, drugs would be much more expensive, and out lives would all be worse as a result. The clinical trials detect nearly all of the major problems associated with drugs, and the yellow card scheme catches the more minor and rarer problems.
There is, however, an annoying problem. Drug trial results are often difficult to get your hands on. Firstly they are published in journals. Journals make their money by selling themselves to scientists and doctors, and are therefore unwilling to give away their articles freely. This means that some trial results cant be found easily. However some are accessible, or at least the abstract (part of article that outlines method and results). Use google scholar (scholar.google.co.uk) to search for trial results (type 'dtap' for example). You can also use the clinicaltrials.gov trial registry, or pubmed (www.ncbi.nlm.nih.gov/pubmed)
Another problem is that drug trials are often difficult to understand. They are packed with high level statistics and biology, and are not written for the lay-person. Regulatory bodies employ scientists and statisticians to analyse and dissect clinical trials so you don't have to. Their job is to work out which drugs are safe, and which aren't, and they're very good at it.
If you really feel like wading though the science them some general tips when reading trial results are:
- The more people in the trial, the better
- Look at who is running the trial (who is paying them?)
- The more citations a article gets (shown in google scholar search results) the better it will be (generally)
- Double blind trials are the gold standard phase 3 trials
- Look at what journal the paper was in. The BMJ, lancet, nature. These are all good journals that generally publish good papers and revoke them if they're found to be rubbish (ie the lancet and the wakefield MMR->Autism paper).
If you are interested in learning more about clinical trials and medical research (and research in general) I would recommend 'Bad Science' by Ben Goldacre.
PS: Most of the search tools I linked in this return high-level scientific results, which may be difficult to interpret. Remember, the job of the regulatory authority is to dig through the trial results so you don't have to. Trust them in general, but know the results are there if you really want to check them.
PPS: Look out for papers by the Cochrane Collaboration, they're a wonderful organisation who combine the results from lots of trials and analyse them together. This allows them to identify problems in drugs that smaller trials are too insensitive to detect.
PPPS: Just found a paper looking at DTAP and IPV: www.ncbi.nlm.nih.gov/pmc/articles/PMC2647469/?tool=pubmed. It was published by the WHO, so its likely to be good quality.Look at the "Reactogenicity" section for safety information.
Here's another paper, 2000 infants were given either the conbination vaccine or individual dtap and ipv vaccines. It lists safety results (the gist of which was 'nothing serious, lots of sore arms') pediatrics.aappublications.org/cgi/content/full/123/1/301
More useful links:
NHS evidence: www.evidence.nhs.uk/default.aspx