Medieval history students excavate long-forgotten rubbish dumps in search of discarded fish and animal bones and shells. Their findings reveal the pattern of life lived by people centuries ago. Similarly osteologists, scientists specialising in human bones, examine the skeletons uncovered by industrial and commercial development in Britain.

The Wellcome Trust has details of 11,000 skeletons uncovered by workmen's spades or mechanical diggers as London changes. When cemeteries or burial pits, including those that contain remains of victims of the plague or other disasters, are uncovered, a team of skilled osteologists makes a detailed study of the bones. These are treated with the same reverential care that would be displayed by archaeologists studying a priceless piece of ancient porcelain.

The Wellcome Trust and the osteological research unit of the Museum of London have built up a database on the collected bones. A selection of the skeletons of London's long-buried dead is now on view at the Wellcome Collection in Euston Road. The skeletons tell a story that has been unravelled by experts: people's age and sex, an idea of the work they did in life, the food they ate, deprivations suffered and diseases that affected them. Examination of the bones, dating from the Norman to mid-Victorian period, records the influence on the population of plenty or poverty, hard labour or leisure and its prevailing health. The skeletons chronicle outbreaks of plague, syphilis and the ravages caused by TB and smallpox.

Smallpox was a hazard for everyone, regardless of class or income. The rich could escape the plague by streaming through Whitechapel, in East London, to the relative safety of the country, but there was no avoiding smallpox. One of the skeletons in the Wellcome Collection is that of a nine-month-old child who caught smallpox but survived long enough for the virus to damage its bones indelibly. Samuel Pepys, the 17th-century diarist, described smallpox as being as common as swearing or eating. The disease was finally eradicated only within my lifetime, and this was achieved by vaccination.

The credit for introducing vaccination against smallpox and the concept of vaccination against diseases is given to Dr Edward Jenner, a GP who settled in a rural practice at Berkeley, in Gloucestershire. He noticed that those who worked with cows and suffered from cowpox, a lesser form of smallpox, did not catch the deadlier version. In 1796 he made history by inoculating a young boy with the serum collected from the sore of a milkmaid who had caught cowpox from one of her cows. Jenner then sat back to watch whether the boy would be protected from smallpox. He was. Despite some initial opposition, the enormous importance of his discovery became almost universally accepted and he became famous.

The Wellcome Collection has several pictures of Jenner, and has also acquired a painting of the almost unknown Benjamin Jesty, a Dorset farmer. Unknown to Jenner, Jesty had vaccinated his own family in 1774 against smallpox using a darning needle. Having had a similar idea to Jenner's, he had collected serum from one of his cows infected by cowpox and scratched it into the arms of his wife and children. This protected them from smallpox.

There are now 27 vaccines available to combat different diseases. They save three million lives a year and prevent many more children from physical or mental disability as a result of various infections. Vaccination and inoculation already protect patients against previously distressing, and sometimes fatal, diseases that includes hepatitis A and B, flu, TB, many forms of meningitis, measles, mumps, rubella, polio, whooping cough, chickenpox, typhoid, diphtheria, tetanus, HPV (and, therefore, cervical cancer) as well as smallpox.

There is more to come. Scientists are busily engaged in research in different stages of development of vaccines against HIV, a better vaccine against pneumococcal pneumonia, glandular fever, shingles, Dengue fever, malaria, other forms of hepatitis, melanoma, herpes, more types of meningitis and rotaviruses - the viruses that regularly cause chaotic epidemics of diarrhoea and vomiting.