Immunization policies and strategies

The 'Expanded Program on Immunization'

Established in 1974 [3], the EPI targeted to achieve 80% immunization coverage of children under the age of 12 months by the year 1990. The immunization goal was further reinforced by the Alma-Ata Declaration in 1978 [14], which identified primary health care, including immunization, as the key strategy for achieving "Health for All by the Year 2000". Interest in immunization was greatly boosted by the global eradication of smallpox in 1977 [4]. While progress towards improving overall coverage was slow in the first half of the 80s, the UN Secretary-General, in 1985, called for all countries to reach at least 80% infant coverage (Universal Child Immunization, UCI). Following renewed efforts in developing countries and by immunization partner agencies, the UCI goal was achieved in 1990.

Up to the early 1990s, the EPI concentrated on establishing the necessary infrastructure (vaccine cold chain, transportation, training of staff) to deliver vaccines to children, and on monitoring coverage. The program then added specific disease control goals during the 1990s: polio eradication, and accelerated control of measles and of maternal and NT (MNT) elimination.

The Children's Vaccine Initiative (CVI), which operated between 1990 and 1999, was a first and innovate attempt to create a global public-private partnership to support global vaccination and make new vaccines available to all children. However, impact of the CVI was not as strong as expected, mainly because critically important partners, such as the major vaccine manufacturers, were not yet sufficiently represented in the initiative.

Since 2000, the GAVI3 has been very successful at re-focusing immunization activities globally. Many strategies outlined by the GIVS document support the GAVI objectives [8]: the introduction of new vaccines, the increasing integration of immunization with other health interventions, and strengthening national immunization programs within the health system context. In GIVS, new goals for the global and national EPI programs were set and supported by a wide collaboration of partners. Among others, the goals called for were:

- by 2010, achieve 90% coverage of children under 1 year of age nationally in each country, with at least 80% coverage in every district;

- by 2010, reduce measles mortality by 90% compared to the 2000 levels, and

- by 2015, reduce overall morbidity and mortality from vaccine-preventable diseases by two-thirds compared to the 2000 level.

3 GAVI partners include governments in industrialized and developing countries, UNICEF, WHO, the Bill and Melinda Gates Foundation, the World Bank (WB), NGOs, foundations, vaccine manufacturers, and technical agencies such as the US Centers for Disease Control and Prevention (CDC)

Table 1. Routine immunization schedule for infants recommended by the EPI

Vaccine

Birth

6 weeks

Age 10 weeks

14 weeks 9 months

BCG

X

Oral polio

Xt

X

X

X

DTP

X

X

X

Hepatitis B* Scheme A

X

X

X

Hepatitis B Scheme B

X

X

X

Haemophilus infl. type B

X

X

+In polio-endemic countries.

'Scheme A is recommended in countries where perinatal transmission of HBV is frequent (e.g., in South-East Asia). Scheme B may be used in countries where perinatal transmission is less frequent (e.g., in sub-Saharan Africa). **In countries where yellow fever poses a risk.

*"A second opportunity to receive a dose of measles vaccine should be provided for all children. This may be done either as part of the routine schedule or in a campaign.

Yellow fever Measles

+In polio-endemic countries.

'Scheme A is recommended in countries where perinatal transmission of HBV is frequent (e.g., in South-East Asia). Scheme B may be used in countries where perinatal transmission is less frequent (e.g., in sub-Saharan Africa). **In countries where yellow fever poses a risk.

*"A second opportunity to receive a dose of measles vaccine should be provided for all children. This may be done either as part of the routine schedule or in a campaign.

Routine infant immunization

Table 1 shows the 'basic' immunization schedule recommended by the EPI/ WHO [15], which is followed in low-income and most lower middle-income4 developing countries. Schedules in most upper middle- and high-income countries start later (e.g., 2 months), with longer intervals between doses [16, 17]. While the basic EPI schedule, with some variation, is still followed by many developing countries, vaccination schedules in middle-income and industrialized countries vary considerably, for historical, epidemiological, and economical reasons (compare the 2006 U.S. Child and Adolescent Immunization Schedule, Table 2). WHO keeps track of and publishes national immunization schedules [18]. To protect mothers and neonates against tetanus, WHO recommends implementing a five-dose tetanus toxoid (TT) schedule [19] for women of childbearing age, especially where most women in this age group have not previously received TT when they were young [20]. The different EPI contacts during the first year of life present opportunities for health education of mothers and caretakers and to deliver other basic health care interventions. For example, the measles contact at 9 months of age is used in many developing countries to administer vitamin A to children.

In developing countries, routine immunization services are delivered most commonly by midwives or nurses in a health center, offering vaccination either daily or on specific days of the week, depending on the number of children attending each day. Where health centers have large catchment

4 Based on the classification of the WB by gross national income; of 208 economies with populations of > 30 000, including 184 WB member countries, 54 are 'low', 58 are 'lower middle', 40 are 'upper middle' and 56 are 'high' income.

Table 2. US recommended childhood and adolescent immunization schedule, as published by the Centers for Disease Control and Prevention at www.cdc.gov/nip/acip

Birth

month

months

months

months

12 months

15 months

18 months

24 months

4-6 years

11-12 years

13-14 years

HepB Series

years

16-18 years

Hepatitis B

HepB

HepB

HepB

HepB

Diphtheria, Tetanus, Pertussis

DTaP

DTaP

DTaP

DTaP

DTaP

Tdap

Wae mop/»Vus influenzae type b

Hill

Inactivated Poliovirus

Measles, Mumps, Rubella

Varicella

Meningococcal

Varicella

Vaccinas wit hih broken lino ira for ■tlecttd population«

Mvw • ■- » m m ■ i", > mm * m « • ■ m p i

Mvw • ■- » m m ■ i", > mm * m « • ■ m p i

Pneumococcal

Influenza

Hepatitis A

Influenza (Yearly)

This schedule indicates the recommended ages for routine administration ol currently licensed childhood vaccines, as of December 1, 2005, for children through age 18 years. Any dose not administered at the recommended age should be administered at any subsequent visit when indicated end feasible. Hi Indicates age groups that warrant special effort to administer those vaccines not previously administered. Additional vaccines may be licensed and recommended during the year. Licensed combination vaccines may be used whenever any components of the combination are indicated and other components of the vaccine are not conttaindicated and if approved by the Food and Drug Administration for that dose of the series. Providers should consult the respective ACIP statement for detailed recommendations. Clinically significant adverse events that follow immunization should be reported to the Vaccine Adverse Event Reporting System IVAERS). Guidance about how to obtain and complete a VAERS form is available at www.vaers.hhs.gov or by telephone, 900-822-7967.

Range of recommended agos Catch-up immunization ^^^ 11-12 year old assessment areas, regular additional 'outreach services' through staff based at the health center may be organized to reach children who live too far away from the center, and to trace children who did not come back for follow-up doses. In other areas it may be necessary to set up mobile services, which are more costly, because vaccination teams need vehicles and spend 2 or more days to reach hard-to-access population groups [21]. Any contact with a child in a facility offering EPI services, whether health center or hospital, should be used to screen the vaccination status of both the child and its mother (TT) and to offer vaccines and a basic package of non-vaccine preventative child health services. Missing opportunities to vaccinate, such as during a visit to the health facility for other reasons, still constitute a major factor contributing to low coverage.

Booster doses and 'second opportunity' for measles vaccination

Few vaccines give life-long protection after the primary series. To maintain immunity beyond childhood, booster doses are needed. To maximize returns of scarce resources, however, WHO recommends considering adding booster doses to immunization programs once they have reached routine coverage levels of 80% or higher. Boosting with BCG is not recommended, as there is no evidence of its efficacy [22].

Since many developing countries have now reached 80% coverage, they have begun to include booster doses in their schedules, based on epidemio-logical patterns of diseases, available resources, and health infrastructure. Events like the diphtheria epidemic in Eastern Europe in the early 1990s, or the recognition that pertussis-infected adults contribute to community spread [23] triggered renewed interest in, and importance attached to, booster doses. While high coverage with one dose of measles vaccine will reduce measles morbidity and mortality, a second vaccine dose is needed for more efficient measles reduction, or to achieve measles elimination [24]. This 'second opportunity' for measles vaccination is not intended as a true 'booster dose' but to give a second chance to seroconvert for children who did not respond to the first dose, and also to reach children who missed the first dose. Increasingly, additional measles vaccine doses in developing countries, intended to reduce measles mortality or to move towards measles elimination, are delivered through campaigns. As the EPI programs mature, WHO encourages adopting routine two-dose measles schedules, to sustain gains in measles mortality reduction [25].

Supplementary immunization activities

Immunization campaigns to supplement routine programs to increase coverage - now often referred to as supplementary immunization activities

(SIAs) - were used first during the early phase of EPI to rapidly increase coverage to reach the 1990 'universal child immunization' (UCI) goal, at that time often with poor results. More recently, SIAs are no longer used mainly to boost overall coverage, but have become the main tools for disease eradication and elimination initiatives - to achieve global polio eradication, reduce measles mortality, mainly in Africa, for measles elimination (in WHO Regions with a measles elimination goal [25]), and for TT campaigns to eliminate MNT, targeting child-bearing age women. SIAs typically target all children in a particular age group, according to disease epidemiology (5 years for polio campaigns, from 9 months to < 15 years for initial measles campaigns), and regardless of previous immunization status. SIAs are used in many countries to provide other interventions, most commonly vitamin A supplementation [26], but also, for example, insecticide-treated bed nets for malaria prevention [27], or de-worming medication. With appropriate support from donors and partners, and with adequate planning, implementation and monitoring/evaluation, recent experience with SIAs to reduce measles mortality and for polio eradication has been good overall.

However, there has also been considerable discussion and controversy about the effects of vaccination campaigns on routine immunization programs and primary health care, particularly about the impact, whether positive or negative, of the polio eradication initiative. Some observers believe that polio eradication has detracted from health service delivery and has been detrimental to an integrated approach to health systems development [28]. Several large field studies on the impact of the polio eradication initiative on health systems concluded that, while SIA planning and implementation may have been detrimental in the short term to general health services, positive long-term synergies exist between polio eradication and health systems [29] (building vaccine-preventable disease surveillance, strengthening cold chain and management and planning for routine immunization, distribution of Vitamin A), but that these synergies must be more systematically exploited [30].

The vaccine cold chain

EPI programs established a system of vaccine transport and storage at appropriate temperature - the cold chain - to assure that vaccine potency is maintained. This vaccination strategy component is particularly critical in tropical developing countries, where logistics and lack of reliable power supply and refrigeration equipment are frequent problems. The WHO recommends that the storage temperature for vaccines used in the EPI at health facilities be between 2 °C and 8 °C, a temperature range determined by the heat sensitivity of oral poliovaccine (OPV) and sensitivity to freezing of other vaccines (DTP, TT, HepB). Live vaccines (OPV, measles, BCG, yellow fever) can be stored in freezers at -20 °C. UNICEF and WHO, in collaboration with manufacturers, have set standards [31] for technologically appropriate cold-chain equipment and helped to develop such equipment, such as ice-lined refrigerators, which can maintain appropriate storage temperature for up to 16 h during power cuts, or refrigerators run on kerosene, gas and solar power in areas without grid electricity. Vaccine temperature is monitored over time during international and domestic vaccine transport using temperature-sensitive cards. More recently, vaccine vial monitors (VVMs) [32], attached to each vial of vaccine procured through UNICEF, have greatly facilitated vaccine use in the field, particularly to extend the 'cold chain' into remote areas during polio eradication campaigns. VVMs measure and indicate 'cumulative' heat exposure by changing color once vaccine potency is threatened. It was realized more recently that inappropriate freezing of freeze-sensitive vaccines is also a problem in many countries, potentially affecting the potency of vaccines with adjuvants (HepB, combination vaccines) [33].

Immunization safety and adverse events following immunization

The goal of immunization is to protect the individual and the community from vaccine-preventable diseases. While modern vaccines are safe and effective, no vaccine is entirely without risk. Effective vaccines may produce some undesirable side effects, which are mostly mild and self limited. Many of the adverse events attributed to the administration of a vaccine are actually not caused by the vaccine, but are either due to programmatic or human error (particularly in developing countries), or are simply coincidental events, which are not causally related to vaccine administration [34]. Surveillance for adverse events following immunization (AEFIs) in many developing countries has confirmed that most adverse events temporally associated with vaccination were not causally but only incidentally associated with vaccination. In cases where the vaccine of the vaccination program is the cause of an AEFI, events resulting from inappropriate handling of vaccines ('program error') are much more common than severe events related to properties of the vaccine itself [35]. Examples for reported serious adverse events related to program error are vaccine reconstitution with the wrong diluent, administration of dangerous drugs for vaccines, contamination of multi-dose vials leading to abscesses or sepsis, or transmission of blood-borne diseases (HIV, hepatitis B or C) through contaminated needles or syringes. If allegations regarding vaccine-related AEFIs are not rapidly and effectively investigated and clarified, confidence in a vaccine or the immunization program can quickly be undermined, even if the vaccine or the vaccination program is not at fault, with possible dramatic consequences for acceptance of vaccination and disease incidence.

As successful immunization programs continue to reduce the incidence of vaccine-preventable diseases, there is increasing public concern, particularly in industrialized countries, about possible risks attributed to vaccines.

During the past decade, different vaccine antigens have been accused of contributing to increases of non-infectious diseases. Recent examples of these are false allegations linking measles-mumps-rubella vaccine to autism (United Kingdom), attributing multiple sclerosis to administration of HepB vaccine (France), and linking Hib vaccine to diabetes mellitus (Finland).

Also, when a disease has been eradicated, even extremely rare adverse events may no longer be acceptable. Following the interruption of wild poliovirus transmission in three WHO Regions, the only polio cases that still occur in OPV-using countries are vaccine associated, which has caused many countries to switch to inactivated poliovirus vaccine. In Finland, the increase in BCG-related osteitis cases, while the incidence of tuberculosis (TB) remains very low, led to switching from universal to risk-group BCG vaccination.

The programmatic importance of vaccine and immunization safety issues, including the need for monitoring and rapid investigation of AEFIs, has been increasingly highlighted by WHO. A Global Advisory Committee on Vaccine Safety was established [36], which has issued position papers on vaccine safety issues, such as the use of thiomersal as preservative in vaccines, or the safety of HepB vaccines.5 All countries are advised to establish a system of monitoring and investigating AEFIs, and to train key health staff on AEFI surveillance, and on how to communicate effectively with the media on vaccine safety issues. High-income countries are starting to utilize new information technology and vaccine registers to monitor AEFIs in a timelier manner. Through linking of vaccine registry information to disease-specific registry information, different advanced epidemiological methods can be utilized to try to understand potential cause-effect relationships.

The safe administration of vaccines is an essential component of immunization safety, the importance of which was not fully recognized during the initial phase of the global EPI. Because of the large-scale improper use of both re-sterilizable and single-use injection equipment (inadequate sterilization, re-use of disposable needles and syringes) [37] in developing countries, WHO and UNICEF have promoted universal use of auto-disable (AD) syringe-needle units. AD syringes can only be used once because of an internal locking mechanism, and have now been widely introduced into immunization programs in developing countries [38]. UNICEF now ,bundles' vaccine shipments with AD syringes and disposal boxes to ensure that safe injection practices are maintained.

It is estimated that < 10% of all injections given worldwide are related to immunizations, and activities to promote the safety of injections in the immunization context are handled in the broader context of overall injection safety. The Safe Injection Global Network (SIGN)6, a global partnership of interested parties, aims to prevent transmission of blood-borne

5 Position papers on immunization safety can be found at http://www.who.int/vaccine_safety/en/

6 Information on the SIGN project can be found at http://www.who.int/injection_safety/sign/en/

disease by reducing the number of unnecessary injections, and ensuring the safety of all injections, including those who apply vaccines, as well as by ensuring safe injection-waste disposal.

Another emphasis has been on proper disposal of injection equipment, such as the use of 'sharps' boxes, appropriate disposal pits, and incinerators to prevent infection of health workers through accidental needle stick injuries and reduce risk to communities [39]. There is also progress in developing needle-free injection technologies, particularly focusing on jet injectors with exchangeable nozzles.

Program monitoring and surveillance for vaccine-preventable diseases

The main aim of an immunization program is to reduce the incidence of, and in some cases to eradicate a disease. Disease-specific morbidity and mortality can best be monitored through disease surveillance systems. In poor countries, surveillance data are often not very reliable: case detection and confirmation is erratic, and laboratory equipment and reagents may not exist. Other means to help maintain and improve the quality of immunization programs are monitoring immunization coverage, measuring antibody and cellular immunity responses, and testing vaccine efficacy using different observational epidemiological methods, as well as monitoring the quality of disease surveillance (completeness and timeliness of reporting) [40].

Program monitoring and surveillance data should be available at national, sub-national and particularly at the district level. For immunization programs, main quality indicators include immunization coverage for the vaccines used, the 'drop-out rate', which measures the proportion of children who start but do not return to finish the vaccine schedule (mainly measured between the BCG and DPT3 contact), and the extent of missed opportunities for immunization. Other program components monitored include injection and immunization safety, cold-chain maintenance and social mobilization and information activities [41]. In developing countries, coverage is monitored by the 'administrative method' - a comparison of routine reports of the number of doses given to children to the estimated population in that age group, or through surveys [42]. Coverage data from different sources and at different levels has often shown considerable discrepancies. WHO and UNICEF have reviewed and compared reported 'administrative' and survey coverage data for all countries since 1980, and then developed 'best coverage estimates' for each country [10]. Best estimates are updated annually, and are often lower than results obtained by the administrative method. However, the iterative processes now used to derive coverage estimates have much improved the accuracy of available coverage data, with continuously declining discrepancies.

Many middle- and high-income countries have better demographic data available for more precise estimation of coverage: total or sample popula-

Figure 3. Global vaccine-preventable disease laboratory network. The designation employed and the presentation of material on this map do not imply the expression of any opinion whatsoever on the part of the secretariat of the World Health Organization concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. Dotted lines on maps represent approximate border lines for which there may not yet be full agreement.

Figure 3. Global vaccine-preventable disease laboratory network. The designation employed and the presentation of material on this map do not imply the expression of any opinion whatsoever on the part of the secretariat of the World Health Organization concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. Dotted lines on maps represent approximate border lines for which there may not yet be full agreement.

tion method is used in these countries. Increasingly, individualized 'numerator data' are available, which allow evaluatation of timeliness of vaccinations in addition to coverage.

Surveillance for vaccine-preventable diseases is an essential program component to measure the impact of vaccines used in routine immunization programs. Surveillance should provide 'data for decision-making' through the ongoing systematic collection, analysis and interpretation of surveillance data, which enables program managers to take decisions on planning, implementation and evaluation of immunization programs. High-quality surveillance remains particularly critical for polio eradication [43] and regional measles elimination [44] efforts, to detect remaining chains of virus circulation and reliably monitor progress towards interruption of transmission. Reliable surveillance data are also critical to establish baseline 'disease burden'7 [45] in countries considering introducing a new vaccine into their immunization program.

Laboratory confirmation is important for some vaccine-preventable diseases, particularly those with eradication or elimination goals. A global poliovirus lab network (Fig. 3) consisting of 145 laboratories all around the world [46] provides critical information to the polio eradication effort,

7 WHO's immunization programme maintains a web site on vaccine-preventable disease burden estimation at http://www.who.int/immunization_monitoring/burden/estimates_ burden/en/index.html including primary virus isolation from stool specimens, intratypic differentiation to distinguish wild- from vaccine-type polioviruses, and genetic sequencing of isolated viruses to track transmission paths of virus strains around the world.

A global measles laboratory network has been established, which has utilized much of the polio laboratory infrastructure; often housed at the same institutions as polio labs, measles labs use similar systems for specimen transport, data management, communication and reporting of results. The measles network's primary roles are confirmation of suspected measles cases using IgM testing and genetic characterization of measles viruses. Measles laboratories also perform serological diagnosis of yellow fever in countries in Africa and Latin America where yellow fever is prevalent. Regional rotavirus laboratory networks are also emerging in some regions [47]. Together with the planned expansion of the African 'Paediatric Bacterial Meningitis Laboratory Surveillance Network', a global vaccine-preventable disease laboratory (both virological and bacteriological) network is evolving [48], which will be a crucial component of the future of vaccination described in GIVS.

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