Herd Immunity
The inherent or acquired immune resistance offered by populations to the prevalence
of a disease in a community is referred to as herd immunity. Vaccinations of
populations play an important role in the development of immunological barriers
toward the entry of a disease into the community (John, 2000; Paul, 2004). This immune
resistance effectively reduces the efficiency of the microbe to transmit from
person to person. Generally, 83% to 94% of the population needs to be vaccinated
to achieve herd immunity to a given disease. Immune levels also depend on the virulence
of the disease. The protection offered by herd immunity to those unimmunized
because of the break in transmission process is called herd protection. Herd
immunity and herd protection are two different terms. The oral polio vaccine offers
both herd immunity and herd protection (because live virus is excreted in stools and
can spread in the community), whereas the inactivated polio vaccine offers only
herd protection. Tetanus vaccination does not provide any additional benefits to the
unimmunized.