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Efficacy and effectiveness

Duration of immunity provided by vaccines

The duration of immunity varies with different diseases and different vaccines. Lifelong immunity is not always provided by either natural infection (getting the disease) or vaccination. The recommended timing of vaccine doses aims to achieve the best immune protection to cover the period in life when vulnerability to the disease is highest.

  • Many vaccines used today are relatively new and data concerning the length of time that they give protection is continually being updated
  • For many diseases immunity wanes following natural infection
  • The duration of immunity provided by vaccines varies depending on a range of factors, particularly the vaccine itself
  • Live vaccines generally induce longer lived immunity than sub unit vaccines
  • Sub unit vaccines frequently require primary courses and boosters
  • Polysaccharide vaccines do not generate long-lived memory cells
  • If the interval between doses is too short the duration of immunity can be affected. – Hence minimum intervals are required
  • In the very young and very old the duration of immunity can be limited

Vaccine immunogenicity

Vaccine immunogenicity is a measure of the immune response to a vaccine and usually involves measuring specific antibodies in the blood. For some, but not all vaccines, a defined threshold of specific antibody levels has been correlated with protection. However, this does not definitively tell us if a person is fully protected against disease. If good immune memory has been established, a large rise in antibody levels occurs following a booster dose of vaccine.

Vaccine efficacy and effectiveness

Vaccine efficacy and effectiveness are measures that compare the rates of disease between vaccinated and unvaccinated people. Efficacy is measured in controlled clinical trials, whereas effectiveness is measured once the vaccine is approved for use in the general population. From these we can identify the proportion of vaccinated people we would expect to be protected by the vaccine.

Herd immunity (also called community immunity) is an important mechanism by which the larger community is protected. For some diseases, if enough people are immune then transmission of the disease is reduced or eliminated. This is particularly so for diseases such as rubella and pneumococcal disease. High vaccine coverage must be maintained in order to prevent the disease re-entering the population.

No vaccine is 100% effective, a small percentage of people are not protected after vaccination and for others the protection may wane over time. Also, some people are unable to be vaccinated due to certain conditions such as immune suppression. Maintaining immunity in those around these people protects them from disease.

Duration of protection by vaccine

Disease  

Estimated duration of protection from vaccine after receipt of all recommended doses 1,2

Comments

Pertussis(whooping cough) 

4-6 years

Immunity from natural infection also wanes. Booster at age 11 years is offered

Diphtheria

Around 10 years

Boosters are recommended in adults at 45 & 65 years of age

Tetanus

96% protected 13-14 years, 72% >25 years

Boosters are recommended in adults at 45 & 65 years of age

Polio

>99% protected for at least 18 years

Boosters offered to those travelling to at risk countries

Haemophilus influenzae type B

>9 years to date

Excellent immunogenicity observed for this vaccine suggesting long-term protection

Hepatitis B

>20 years to date

Likely lifelong for those who have seroconverted but >20 years has been observed to date

Measles

Life-long in >96% vaccines

Community protection is important to stop transmission to those too young to be immunised, or those who cannot have the MMR vaccine

Mumps

 >10 years in 90%, waning slowly over time

 Duration of immunity varies in different populations. It is not as long-lived as measles or rubella

Rubella

Most vaccinees (>90%) protected >15-20 years

Community protection is important to stop transmission to those too young to be immunised, or those who cannot have the MMR vaccine

Pneumococcal

 >4-5 years so far for conjugate vaccines

To date antibody concentrations have remained high in vaccinees. Community protection means vaccinating children reduces the disease in all ages in the community

Human papillomavirus

>5-8 years to date

 Response following antigen challenge indicates immunity from vaccine likely to be very long term

Community immunity has been observed

Varicella

One dose - unknown

Two doses >14 years to date

Mild breakthrough disease can occur within 2 years when only one dose is given. Immunity is boosted when virus is still in circulation

Community immunity plays an important role is disease control

Key references

  • Plotkin, S.A., W.A. Orenstein, and P.A. Offit, Vaccines. 5th ed. 2008, Pennsylvania: Elsevier Inc
  • According to the current NZ Immunisation Schedule1
  • Plotkin. Vaccines. Fifth Edition. 2
 

Last updated: Apr 2017