What decides which vaccines can be combined?

OK, we all know that we can successfully vaccinate against a lot of very dangerous and potentially deadly diseases now. What decides which of those vaccines can be combined into a single dose? (As in MMRV (Measles, Mumps, Rubella (German Measles), and Varicella (Chickenpox)) and DPT (Diphtheria, Tetanus, and Pertussis (Whooping Cough)).) I’m guessing it isn’t possible to combine all of the vaccines needed before, say, the age of six (the first cutoff age in the CDC schedule) into a single dose, right?

I really am curious, so I’m bumping this.

I am pretty sure that they have to do brand new clinical trials to make sure combining them is not harmful. I would guess that they combine vaccines that are not likely to cause problems when they are put together. As far as who has the idea to combine them, it’s very likely that comes from a drug company that makes them.

That’s right. It is up to the manufacturer to choose the combinations of antigens and to show the FDA that the combinations being proposed at the doses proposed are both safe and effective (or, when it isn’t possible to study effectiveness in humans directly, as with rabies, that the preparation is immunogenic). In the case of the new adult/adolescent tetanus, diphtheria, pertussis vaccines now used in the U.S., the manufacturers also did studies to show that you could give the vaccines at the same time as other vaccines recommended at the same age (e.g., meningococcal conjugate vaccine, HPV vaccine).

The manufacturers provide the information to the FDA. The FDA staff review the data and present it to an expert panel which makes a recommendation for or against licensure for a specific use at a specific dose with specific packaging and a specific package insert. Then the FDA Commissioner decides what to approve.

Starting months before a new vaccine is expected to be licensed, experts on the staff of the CDC look at ALL the relevant literature on safety and effectiveness and present it to an ad hoc panel of experts (mostly academics and federal scientists) in an exhaustive, months long process. At the end of the process, right after the vaccine is licensed, the recommendations and the data analysis supporting them are presented to an external group of experts, the Advisory Committee on Immunization Practices, that votes to approve all or some of the recommendations or to modify the recommendations. The Director of the CDC then decides whether or not to accept the recommendations.

The above is a bit simplified but you can get an idea of the thinking that goes into putting a combination vaccine on the market and getting it recommended by the ACIP if you go to the CDC web site, look under vaccinations for ACIP recommendations, and then look at the recommendations published in about 2007 for the use of Tdap vaccine in adults and adolescents.

I’m in the middle of my US immigration ordeal, and recently had to get my USCIS physical, conducted by a DHS-approved Civil Surgeon. One of the requirements is evidence of a whole range of vaccinations.

I had evidence of MMR, and they did a tuberculosis test in my forearm, but they also gave me four different vaccinations at the same time—tetanus, influenza, Hep A, and Hep B. Between those four shots (two in each shoulder), the Varicella puncture in my forearm, and drawing three vials of blood (some from each arm) for HIV, Syphillis, and Varicella tests, i felt like a bit of a pincushion.

And i had a horrid fever for the next 24 hours, which some internet research suggested was probably a side-effect of the flu shot. I also wondered if combining all those vaccinations at the same time might have exacerbated the situation.