Killed vaccines consist of suspensions of killed organisms such as typhoid, cholera, and pertussis (although there is now an acellular vaccine) or one of the products or fractions of the organisms. These include toxoids of diphtheria and tetanus and subunits of viruses such as surface hepatitis B antigen. Among the most successful of these types of vaccines has been the use of polysaccharides in the pneumococcal, meningococcal and haemophilus influenza vaccines. In general, the killed vaccines are not as effective as the live viruses because they do not give long-lasting immunity as a live infection does. For example, although the tetanus toxoid vaccine is effective, it requires a booster dose every ten years.