Inactivated vaccines (such as inactivated polio vaccine or killed pertussis vaccine) and purified protein vaccines (such as diphtheria and tetanus toxoids, Hib vaccine, and hepatitis B vaccine) do not have any living germs in them. These vaccines stimulate the immune system without causing any infection. Live, attenuated vaccines (such as measles, mumps and rubella vaccines) do infect cells and multiply in the body. The vaccine viruses have been sufficiently weakened, or attenuated, in the laboratory that they stimulate immunity without causing a full-blown infection. They do not spread from a vaccinated child to another person. Oral polio vaccine (OPV), however, not only infects the intestinal tract, but is also excreted in the feces. The vaccine strains can spread from person to person. Such spread is usually helpful, though, because those who get the polio vaccine virus this way may also become immunized. OPV is a very safe and effective vaccine. There is, however, an incredibly small risk of getting paralytic polio from the vaccine. The most recent estimate of the risk of vaccine-associated paralytic polio after the first dose of OPV (given to infants) is 1 out of every 1.3 million doses. The risk is much smaller for susceptible persons exposed to a vaccinated child. To avoid the very small risk of disease associated with the oral vaccine, all Canadian provinces except Manitoba have switched to the inactivated polio vaccine (IPV). Switching to IPV should maintain the remarkable accomplishment of eradication of paralytic polio in the Western Hemisphere.

This document was published by the Canadian Paediatric society, 1997.

Posted by the Canadian Paediatric Society, July 1997.

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