We currently vaccinate children routinely against 14 different diseases. Some vaccines protect after only two doses, while others require up to 5 doses for full protetction. As a result, by age 5 a child has usually had 36 doses of vaccines against 13 of those diseases, and 6 doses of influenza vaccine. These are a lot of vaccines -- and, if they are given separately, a lot of pokes.
Fortunately, we have always had some vaccines that can be combined into single shots that protect against multiple diseases. An early example was the vaccine against diphtheria, pertussis (whooping cough), and tetanus. The original combination vaccine, which included a pertussis vaccine made from whole but killed pertussis bacteria, was known by its "initials" as DTP or DPT; it was replaced in the late 1990's by DTaP or DPaT, which is also a "3-vaccine vaccine" that contains an acellular pertussis vaccine -- one that contains only enough "pieces" of the pertussis bacteria to help a child become immune, but not enough to cause the fever that was often seen with DPT. Another long-used and well-known combination vaccine is MMR, which protects the recipient against measles (actually rubeola, or "ordinary" measles), mumps, and rubella, or "German" measles.
DPaT and MMR are still widely-used vaccines. However, there are several other combination vaccines on the market, These include:
Depending on which of the combination vaccines are used, it's possible to cut the number of shots a child needs by age 5 years from 21 (using DPaT and MMR but no other combinations) to 14. That's not too bad.
There has been a lot of speculation in the media about whether or not the combination vaccines have more side effects than the individual vaccines, and some parents ask whether their child can or should be given the individual vaccines rather than the combinations -- even for the older combinations like DPaT and MMR. It is very hard to obtain the individual vaccines for measles, mumps, or rubella, and almost impossible to obtain individual diphtheria, pertussis, or tetanus. (Even the adult tetanus/diphtheria vaccines are available only in combination form.) The combination vaccines have so far worked just as well as the individual vaccines did, and with no proven side effects. The speculation that there is as association between MMR and autism is a speculation that has never been proven by scientific evidence. And I personally wouldn't want to inflict that many extra shots on my child.