• For the individual

  Efficacious vaccines protect individuals if administered before exposure.

  Pre-exposure vaccination of infants with several antigens is the cornerstone of successful immunization programmes against a cluster of childhood diseases.

  Many vaccines can also protect when administered after exposure – examples are rabies, hepatitis B, hepatitis A, measles and varicella.

• For society

  It is estimated that vaccines annually prevent almost 6 million deaths worldwide.

  In field trials, mortality and morbidity reductions were seen for pneumococcal disease in sub-Saharan Africa and rotavirus in Latin America.

  Specific vaccines have also been used to protect those in greatest need of protection against infectious diseases, such as pregnant women, cancer patients and the immunocompromised.

• Herd protection

  Efficacious vaccines can not only protect the immunized, but can also decrease the incidence of disease among unimmunized individuals in the community through “indirect effects” or “herd protection”.

  Herd protection may also be conferred by vaccines against diarrheal diseases, as has been demonstrated for oral cholera vaccines.

  “Herd protection” of the unvaccinated occurs when a sufficient proportion of the susceptible group is immune. Vaccination prevents the spread of an infectious agent by decreasing the amount and/or shortening duration of pathogen shedding by vaccines, which retards transmission in the crowd. So, the proportion of decline in disease incidence is greater than the portion of individuals immunized.

  Some diseases can be eliminated even without 100% immunization coverage due to herd protection.

References:

1. Who.int. 2021.?Immunization coverage.

[online] Available at: < https://www.who.int/news-room/fact-sheets/detail/immunization-coverage > [Accessed 19 May 2021].

2. Who.int. 2021.?WHO | Vaccination greatly reduces disease, disability, death and inequity worldwide.

[online] Available at: < https://www.who.int/bulletin/volumes/86/2/07-040089/en/ > [Accessed 19 May 2021].