Vaccination

Vaccination1 works by exposing an individual to a killed or weakened infectious organism or part of an organism, usually via injection. This stimulates the immune system to respond quicker to future exposure to that organism, preventing the disease or reducing its severity. Risks of naturally acquired infection are avoided.

Many different vaccines are available, usually targeted at specific groups. For example, routine vaccinations aimed at all children, targeted vaccinations for at-risk individuals or populations, and travel vaccines. UK policy is detailed in the Green Book, a continuously updated online reference document.2

That vaccination works is certain. However, vaccines are not available against all important infections. Vaccine against HIV for example remains elusive.3 Where vaccines are available, their efficacy can vary e.g. vaccine efficacy against tuberculosis (TB) is 0 -80%, depending on patient group and type of TB.4

Evidence for possible benefits

Protection against infectious disease through vaccination is one of the most cost-effective health interventions available.5 Voted the 4^th greatest medical milestone since 1840,6 it saves 2-3 million lives globally each year.2 Recent UK-based successes include vaccination against Haemophilus Influenzae type B (Hib), an important cause of serious invasive childhood disease including meningitis and epiglottitis. In 1991, the year before Hib introduction into the routine child immunization schedule, there were 803 cases of invasive disease in children aged under 5 years in England and Wales (20.5/100,000 children under five years of age). By 1998, that had dropped to only 21 cases (0.65/100,000 children under five years of age).2

Evidence for possible risks

Despite their continued importance, even in developed countries like the UK, vaccination programmes have often aroused heated controversies. Like any intervention, vaccines have risks ranging from:

• Minor side-effects e.g. injection-site pain; post-vaccine fever.
• Major (usually rare) adverse reactions e.g. anaphylaxis.

Unfortunately, unproven myths can be just as influential as scientifically robust data. Notable in recent years is the discredited 1998 theory about the measles-mumps-rubella (MMR) vaccine causing autism.7 In 2011, this continues to have implications for the ongoing measles outbreak in Europe.8 Paradoxically, vaccine success is itself partly to blame: some diseases are now so uncommon that people no longer appreciate how serious they can be. Consequently, some underestimate the risks of disease whilst overestimating potential risks of vaccine harm.

Implications for health and well-being

To justify vaccination, policy makers must balance population benefits against the risks and costs. Individuals doing the same but coming to different conclusions (usually based on different perceptions of benefit/risk balance) can lead to tensions which need to be sensitively managed:

• In the UK, vaccination is not generally obligatory (an exception being healthcare workers who can be excluded from certain duties unless immune to Hepatitis B). Where policy makers determine that vaccination plays an important role in disease control, resources need to be devoted to increasing take-up;9
• Ethical discussions can sometimes arise e.g. about sexual promiscuity and human papillomavirus vaccine;10
• ‘Herd immunity’ is critical for societal health. Once a sufficient proportion of the at-risk population are vaccinated (up to 85-95%, depending on disease), then disease spread is limited. Unvaccinated individuals are indirectly protected. These include infants too young to be vaccinated and patients whose poor health does not allow safe vaccination. It also includes those who could be vaccinated but choose not to be. Herd immunity means that there is no such thing as a purely individual decision to remain unvaccinated: each non-immune individual does not contribute to the herd and potentially puts others at risk. 

Author: Dr Marko Kerac, Specialty Registrar & Clinical Lecturer, Public Health, LKSS Deanery & University College London

References
1.  The terms ‘immunisation’ and ‘vaccination’ are often used interchangeably. They do however differ. Immunisation is the process of acquiring immunity against infection. Vaccination is a specific type of immunisation which involves an administering a biological preparation in order to induce immunity. It derives from Edward Jenner’s 1796 use of cow pox to prevent smallpox (vacca = cow in Latin)

2. Department of Health. Green book. Immunisation against infectious disease Available athttp://www.dh.gov.uk/en/Publichealth/Immunisation/Greenbook/index.htm Accessed 2 August 2011

3. Harris JE. Why we don’t have an HIV vaccine, and how we can develop one. Health Aff (Millwood) 2009; 28(6):1642-54.

4. Barreto ML, Pereira SM, Ferreira AA. BCG vaccine: efficacy and indications for vaccination and revaccination. J Pediatr (Rio J). 2006; 82(3 Suppl):S45-54.

5. http://www.who.int/topics/immunization/en/ Accessed 1 August 2011

6. Worboys M. Vaccines: conquering untreatable diseases. BMJ 2007; 334(suppl 1):s19.

7. Madsen KM, Vestergaard M. MMR vaccination and autism: what is the evidence for a causal association? Drug Safety 2004; 27(12):831-40.

8. http://www.hpa.org.uk/hpr/archives/2011/news2911.htm#msls Accessed 8 August 2011

9. Smedley J, Poole J, Waclawski E, Stevens A, Harrison J, Watson J, et al. Influenza immunisation: attitudes and beliefs of UK healthcare workers. Occup Environ Med 2007; 64(4):223-7.

10. Hilton S, Hunt K, Langan M, Bedford H, Petticrew M. Newsprint media representations of the introduction of the HPV vaccination programme for cervical cancer prevention in the UK (2005-2008). Soc Sci Med 2010; 70(6):942-50.