Duration of Protection, 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. This usually involves measuring specific antibodies in the blood after vaccination. Immunogenicity gives an estimate of protection for some vaccines, but does not definitively tell us if a person is protected against disease. Large rises in antibody levels following a booster dose indicate that good immune memory is present and suggests that good protection is likely.

Vaccine efficacy

Vaccine efficacy is measured by comparing the rates of disease between vaccinated and unvaccinated people in clinical trials. From this 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. A disease may be controlled in a community by immunisation but 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 years to date  Response following antigen challenge indicates immunity from vaccine likely to be very long term.

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