As a carbohydrate chemist, Dr. Harold Jennings has made significant contributions to the understanding of polysaccharide structures and conformations. He obtained a U.S. patent for his work in 1982 on a novel conjugation procedure which has become the basis of his work on vaccines.

At the National Research Council's Institute for Biological Science, Dr. Jennings specializes in the study of polysaccharides of important human pathogenic bacteria, particularly their structure, conformation, immunobiology and role in causing disease. He has also studied and developed synthetic vaccines against disease caused by these bacteria.

Dr. Jennings and his team are best known for work on vaccines for infant meningitis. Every year in Canada, 400 people catch meningitis and 100 die within 48 hours. Tragically, two-thirds of the people who catch it are under the age of five. The team has developed vaccines to fight the bacterium which causes infant meningitis. Vaccines against meningitis, based on bacterial capsular polysaccharides, have been around for a while, but with serious limitations. None were effective in infants. The limitation was overcome by linking the polysaccharide to a protein carrier to form a new generation of conjugate vaccines.

The vaccines developed by Dr. Jennings fight meningitis caused by the three major strains of Neisseria meningitidis (groups A, B, and C). In addition, he developed conjugate vaccines against meningitis caused by other organisms, for example type b Haemophilus influenzae and group B streptococcus. In 1996, following successful vaccination trials in monkeys, the synthetic group B meningococcal conjugate vaccine conceived by Dr. Jennings for pediatric and adult indications was produced.