Epidemiological Bulletin
      Vol. 17, No. 1
March 1996  



The introduction of new or improved vaccines in national vaccination programs should be preceded by a determination of the intervention's priority through analysis of the epidemiological parameters of each country, a clear definition of the strategies and standards for use of the vaccines (vaccination schedule, age groups, number of doses, and vaccination techniques), and considerations related to the resources needed to ensure constant availability of the vaccines in the health services.

Furthermore, when a new vaccine is about to be incorporated in a national vaccination program, this action should be preceded by an intensive mass communications program to inform the population about the vaccine, its use, and the desease that is going to prevent, since the incorporation of new vaccines in the vaccination programs generally implies additional visits by boys and girls to the health services, and often additional injections which may lead to resistance among population.

Briefly described below are examples of some of the vaccines already available for use in special population groups and/or risk areas for certain diseases. These vaccines are being introduced or are under consideration for introduction in countries in Latin America and the Caribbean.

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Hepatitis B vaccine

Acute viral hepatitis is a serious infectious disease caused by different types of virus (A, B, C, Delta, E) that differ not only in their mode of transmission and their epidemiological, clinical, and immunological characteristics but in the means of their prevention and control.

The hepatitis B virus has been identified as a carcinogenic agent and is estimated to cause nearly 80% of all hepatocellular carcinomas worldwide. The hepatitis B vaccine prevents all forms of transmission of the infection: perinatal, percutaneous, transfusion-related, and sexual.

Two types of vaccines are available: surface antigen of hepatitis B virus (HBsAg), produced from purified human plasma, and another obtained through genetic engineering (recombinant DNA). The two vaccines are safe, immunizing, highly effective (>90%), and produce very few adverse reactions. They are administered intramuscularly, usually in a series of three doses, the first two within at least one month of each other, and the third dose administered 6 to 12 months after the first. The dose varies with the age of the population to be vaccinated: 5-10 mcg (children) and 10-20 mcg (adults).

The vaccination schedule is flexible with regard to the dosage interval; hence, the vaccine can be easily incorporated into the EPI. It should be kept refrigerated at 2-8 C and should not be frozen. It should be noted that the vaccine is characterized by high thermostability.

The recommended vaccination strategy depends on the prevalence of infection in the populations of the targeted regions and in high-risk groups (health workers, homosexuals, intravenous drug addicts, etc.). The areas of risk are defined as:

The Technical Advisory Group for the EPI does not recommend universal vaccination of children in the countries of the Region. Its recommendation is that hepatitis B vaccine be considered for use in populations or areas at risk for the disease. Universal vaccination should only be considered if the available resources permit a supply of this vaccine without jeopardizing the supply of the other vaccines routinely being utilized. In addition, surveillance activities should be undertaken in order to improve information on the disease and to measure the impact of the strategies utilized on the incidence of the disease in the short and medium term and on hepatocellular carcinoma in the longer term.

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MMR Vaccine (Measles, Mumps, Rubella)

The MMR is a combination vaccine against measles, mumps, and rubella, made from attenuated live virus.

The vaccine should be kept under refrigeration at 2-8 C in the health services. For extended storage it should be frozen.

A single deep, subcutaneous dose of 0.5 ml is administered to children from 9 months of age on. The recommended vaccination schedule indicates between 12 and 18 months of age. It is approximately 95% effective.

The fundamental reason for using the vaccine containing the rubella antigen is to prevent congenital rubella syndrome. For adequate control of this syndrome women of childbearing age should be protected against rubella before pregnancy.

The percentage of infection in the fetuses of mothers infected by rubella during the first trimester of pregnancy is greater than 80%. As a result, the target group for the vaccination is all women of childbearing age. For short-term reduction in the congenital rubella syndrome the following actions are recommended:

  1. Vaccination of all women of childbearing age with a vaccine containing the rubella antigen: Measles-Mumps-Rubella (MMR), Measles-Rubella (MR), or Rubella);

  2. Vaccination of most girls and boys between 5 and 18 years of age with MMR, MR, or Rubella vaccine.

  3. Inclusion of the MMR vaccine in the routine vaccination schedule for boys and girls.
It is important to note that the simple addition of the MMR vaccine in child vaccination programs will not reduce the incidence of congenital rubella syndrome for approximately 20 years. In some programs for rubella control, one of the recommended strategies is to vaccinate school-age girls (10-14 years) not previously vaccinated in order to increase the impact on prevention of congenital rubella. Clearly, the exclusive immunization of school-age girls will have an impact on this syndrome but will not interrupt transmission of the rubella virus, since it will continue to circulate among boys of this age.

The following epidemiological surveillance measures should be undertaken with the introduction of this vaccine:

  1. Every suspected case of measles that is IgM negative for the measles virus should be studied for rubella;

  2. Surveillance of congenital rubella syndrome should be undertaken; and

  3. Surveillance of diseases accompanied by fever and skin eruptions during pregnancy should also be instituted.
Introduction of the MMR vaccine or another vaccine containing the rubella antigen should only take place when there is a policy for the control of congenital rubella syndrome or of the disease in the long term and when it is certain that the resources to support a long-term program will be available.

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Haemophilus influenzae B Vaccine (Hib)

Invasive infections by H. influenzae, type b are a major cause of bacterial meningitis in the first years of life. Hib is responsible, moreover, for epiglottitis, septicemia, septic arthritis, osteomyelitis, pericarditis, pneumonias, and otitis.

Vaccines derived from capsular polysaccharides yielded good immunogenicity in adults, but were not as effective in inducing levels of protection in the group at greatest risk (infants under 18 months). However, when conjugated with protein, they became protective in this age group.

Several conjugated vaccines have been developed that are safe and 95% effective. They should be refrigerated at 2-8 C. They are administered intramuscularly or subcutaneously in a dose of 0.5 ml. There is no report of significant adverse reactions. The recommended vaccination schedule is three doses at 4-week intervals, beginning at 2 months of age.

Application in the developing countries on a grand scale should be preceded by epidemiological studies on the patterns of the disease, and providing a breakdown of the prevailing type of Haemophilus influenzae and its effects on child morbidity and mortality by age and risk groups. In addition, a cost-benefit analysis should be done and the priorities regarding public health problems determined. However, when high mortality from meningitis attributable to Hib is identified and the vaccine is available, vaccination of the affected population is recommended.

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Typhoide Fever Vaccine

Typhoid fever is a bacterial disease caused by Salmonella typhi and causes many mild and atypical infections related to the poor sanitation conditions and hygiene of the population. Systematic vaccination is not currently recommended. However, the strategy of vaccinating people at risk in endemic areas or in epidemic situations is utilized.

Three types of vaccines are available; they should be kept under refrigeration at a temperature of 2-8 C:

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Yellow Fever Vaccine

Yellow fever is an acute viral infection of short-term duration and varying severity. The case-fatality rate among indigenous populations of endemic regions is under 5% but may exceed 50% in nonindigenous groups and in epidemics. The disease confers lasting immunity.

The vaccine is manufactured from attenuated live virus. It confers excellent immunogenicity (>95%), high safety, and protection. Immunity lasts at least 10 years. The recommended schedule in all endemic countries, geared mainly toward risk groups (migrant workers, rural population, travelers, etc.) consists of a single dose, administered subcutaneously, after 6 months of age. The dose per person should contain a minimum titre of 1,000 DL. In endemic regions it should be integrated into the EPI routine and administered simultaneously with the measles vaccine.

The yellow fever vaccine should be refrigerated. For extended storage, it keeps better frozen (-20 C).

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Meningococcal Meningitis Vaccine

Meningococcal meningitis is an acute systemic infection caused by the Neisseria meningitidis (meningococcus) bacterium, which is characterized by different serogroups (A, B, C, Y, and W135). It occurs in endemic or epidemic form, causing high mortality and child morbidity, mainly in the under-4 age group. Historically, serogroup A strains have been responsible for the principal epidemics described, but epidemics of serogroup B have recently occurred in the Region.

Currently, there are safe and effective vaccines derived from capsular polysaccharides in different combinations. However, they are not very immunizing in children under 2, and the duration of protection is short, its integration into routine child vaccination programs is not recommended. Nonetheless, they are considered highly effective and important for the control of epidemics. They are thermostable and should be refrigerated at 2-8 C.

Three types of vaccines are available:

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Pneumococcus vaccine

Streptococcus pneumoniae (pneumococcus) is a major cause of severe pneumonia, bacterial meningitis, and a host of infections that are responsible for high morbidity and mortality in children under 5 years and adults.

Derived from capsular polysaccharides, the most commonly used vaccine is comprised of 23 serotypes that account for over 90% of the infections. The vaccine elicits a good immunological response in older children and adults, but because of its low effectiveness in children under 2 years it is not recommended for use in routine child vaccination programs.

In some countries the recommended schedule is the administration of a single dose of 0.5 ml (containing each of these 23 polysaccharides), either subcutaneously or intramuscularly, in adults and children over 2 at high risk (chronic disease, renal insufficiency, cardiovascular disease, immunodeficiency, etc.). The vaccine should be refrigerated at 2-8 C and may be administered simultaneously with other vaccines.

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Considerations for including a new vaccine

When a new vaccine is about to be incorporated in a national vaccination program, this action should be preceded by an intensive mass communications program to inform the population about the vaccine, its use, and the disease that it is going to prevent, since the incorporation of new vaccines in the vaccination programs generally implies additional visits by boys and girls to the health services, and often additional injections, which may lead to resistance among the population.

Source: Special Program on Vaccines and Immunization (SVI), PAHO.

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