ANALYSIS

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World Immunization Week 2015

WHO’s World Immunisation Week 2015 is launched today with the message “Close the immunization gap”. It draws attention to the Global Vaccine Action Plan and the 5 of 6 targets, which the world is not on track to achieve in 2015.

The message focuses on the 21.8 million infants – equal to 1 in 5 of the world’s infants – who do not receive the third diphtheria-tetanus-pertussis vaccine (DTP3). The message states that up to 3 million lives are being saved each year by vaccines while 1.5 million still die from vaccine preventable diseases.

But if we want to focus on child mortality, merely calculating the number of deaths caused and averted by vaccine preventable diseases and coverage of DTP3 is insufficient. Vaccines have more wide ranging effects than specific disease protection.


WHO’s World Immunisation Week 2015 is launched with the message “Close the immunization gap” and a focus on the 5 of 6 targets set out in the Global Vaccine Action Plan which the world is not on track to achieve in 2015.

The five targets which the world is not on the track to achieve are:

  • 90% coverage for the third dose of diphtheria-tetanus-pertussis vaccine (DTP3)
  • Eliminate rubella from 2 regions
  • Eliminate measles from 3 regions
  • Eradicate Polio
  • Eliminate maternal and neonatal tetanus

In contrast, the one target which has been achieved is:

  • Introduction of new- or underutilised vaccines in 90 countries.

WHO’s campaign message focuses on the 21.8 million infants, 1 in 5 of the world’s infants, who do not receive DTP3. The message states that up to 3 million lives are being saved each year by vaccines while 1.5 million still die from vaccine preventable diseases.

But if we want to focus on child mortality, merely calculating the number of deaths caused and averted by vaccine preventable diseases and coverage of DTP3 is insufficient. Vaccines have more wide ranging effects than specific disease protection: in addition to inducing immunity against the targeted diseases, vaccines train the immune system changing the ability to combat other diseases.

Non-specific effects of vaccines

These non-specific effects of Bacillus Calmette Guerin (BCG), DTP and measles vaccine were reviewed by the WHO in 2014. For the live BCG vaccine against tuberculosis, the review concluded that the results “indicated a beneficial effect of BCG on overall mortality” and that the “Estimated effects are in the region of a halving of mortality risk.

For measles vaccine the effect was also beneficial and in the range of halving of mortality risk. In contrast for DTP “the findings were inconsistent, with a majority of the studies indicating a detrimental effect of DTP”. Hence, if we want to improve child survival we should focus on achieving high coverage for BCG and MV. This is currently not being encouraged by the vaccination programme.

If we want to utilise the beneficial effect of BCG optimally, we should ensure that the BCG vaccine is given early, when mortality is highest. When we assess vaccination coverage by 12 months of age and use DTP3 as the main indicator there is no incentive to provide BCG early.

In 45 low- and middle-income countries, less than half of the infants had received BCG during the neonatal period. A major reason for this delay is that the BCG vaccine is supplied in 20-dose vials which have to be used within 6 hours.

In many low-income settings, the vials are therefore not opened unless most doses can be used. In Guinea-Bissau, many children do not receive BCG at their first contact with the health system, as opening a 20-dose vial requires that at least 10 children are due to be vaccinated. Hence, only 38% of children are vaccinated by 1 month of age. When the programme efficiency indicators are wastage levels and vaccinations coverage by 12 months, and when the acceptable wastage margins are narrowed year by year the delays are not likely to be reduced.

Similarly for measles vaccine which is supplied in 10-dose vials, the focus on vaccine wastage and coverage by 12 months of age has led to declines in measles vaccination coverage. It is not currently taken into account that the sequence in which vaccines are given matters: Measles vaccine followed by DTP deprives the child of the beneficial effect of the measles vaccine.

The elimination and eradication targets rely on both routine vaccination strategies and on campaigns. Strengthening the routine vaccination programme can contribute greatly to these targets. However, reaching a high DTP3 coverage is not the aim, reducing mortality is. Studies have not shown a beneficial effect of DTP on child survival. The gap we should measure is therefore not the proportion of children not immunised with DTP3, but the portion of children who have not received measles vaccine and the proportion of children who have not received BCG within the first week of life.

For more information about vaccines and their impact on global health:

 

References:

  1. Organization WH. Close the Immunization Gap. 2015. http://who.int/campaigns/immunization-week/2015/en/ (accessed 24-04-2015).
  2. Organization WH. Global vaccination targets ‘off-track’ warns WHO. 2015. http://who.int/mediacentre/news/releases/2015/global-vaccination-targets/en/ (accessed 24-04-2015).
  3. Benn CS, Netea MG, Selin LK, Aaby P. A small jab – a big effect: nonspecific immunomodulation by vaccines. Trends in immunology 2013; 34(9): 431-9.
  4. Higgins JPT, Soares-Weiser K, Reingold A. Systematic review of the non-specific effects of BCG, DTP and measles containing vaccines . Available at: http://www.who.int/immunization/sage/meetings/2014/april/3_NSE_Epidemiology_review_Report_to_SAGE_14_Mar_FINAL.pdf?ua=1, 2014.
  5. Clark A, Sanderson C. Timing of children’s vaccinations in 45 low-income and middle-income countries: an analysis of survey data. Lancet 2009; 373(9674): 1543-9.
  6. Thysen SM, Byberg S, Pedersen M, et al. BCG coverage and barriers to BCG vaccination in Guinea-Bissau: an observational study. BMC Public Health 2014; 14(1): 1037.
  7. World Health Organization. WHO-UNICEF Guidelines for Comprehensive Multi-Year Planning for Immunization, 2013.
  8. Fisker AB, Hornshoj L, Rodrigues A, et al. Effects of the introduction of new vaccines in Guinea-Bissau on vaccine coverage, vaccine timeliness, and child survival: an observational study. The lancet global health 2014; 2(8): e478-87.
  9. Aaby P, Jensen H, Samb B, et al. Differences in female-male mortality after high-titre measles vaccine and association with subsequent vaccination with diphtheria-tetanus-pertussis and inactivated poliovirus: reanalysis of West African studies. Lancet 2003; 361(9376): 2183-8.

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