Tracking disease and measuring vaccine success

The World Health Organization (WHO) leads and coordinates issues pertaining to international health. WHO consists of 194 member countries and is organized into six regions:

• African Region
• Region of the Americas
• Eastern Mediterranean Region
• European Region
• South-East Asia Region
• Western Pacific Region

The work of the WHO is carried out by experts working with health officials in regional and local offices of countries in which they are employed, and by an extensive network of laboratories around the globe. These offices and labs confirm cases of disease, track changes to viruses and bacteria, track movement of diseases throughout the world, coordinate disease control efforts and monitor the success of interventions, such as vaccine programs.

Types of vaccine programs

Several different types of vaccine programs are available. The best method of delivering vaccines varies depending on geography, disease prevalence and culture. Vaccine coverage for a population can be accomplished by:

• Public sector immunization programs — Vaccines are provided by the government for the entire population. The U.K. has this type of program.
• Public and private sector immunization programs — Vaccines are distributed by both private healthcare providers and government programs. The U.S. has this type of program.
• Mass campaign — A limited time effort (e.g., one day) in which an entire portion of the population (e.g., all children younger than 5 years) is immunized regardless of previous immunization status. These types of campaigns may take place in a certain region or throughout an entire country. Polio eradication efforts have employed mass campaigns in many developing countries.
• Health centers or health posts — Established health centers in a country may provide immunizations on an ongoing basis or specially scheduled days. The Ministry of Health, a non-governmental organization, or a private provider may operate these centers.
• Mobile teams — Immunizations are distributed by teams that travel to villages or remote areas that may not have regular access to healthcare. Nepal and India are places in which these types of efforts have been employed.

Goals for vaccine programs

The measure of success for different vaccine programs may vary, depending on the disease, geographic location and maturity of the vaccine program:

• Disease control is meant to decrease the occurrence of disease in a specific geographic area to an acceptable level.
• Elimination is meant to stop transmission of disease in a given geographic region. Polio has been eliminated from most, but not all areas of the world.
• Eradication is meant to reduce disease to zero worldwide. Smallpox is the only disease that has ever been successfully eradicated. A disease can be eradicated only if it has certain characteristics:
  • Only be found in humans (not animals)
  • Has an easily recognizable illness
  • Not lead to long-term or chronic infection
  • Has an effective intervention, such as a vaccine that provides long-lasting immunity

Variation among vaccine schedules

Vaccine schedules vary from country to country and sometimes even within countries. These differences can include which vaccines are recommended, who should get them, when they are given, and how many doses are needed. There are several reasons for this variation:

Why are different vaccines recommended in different places?

• Economics — Because some countries cannot afford to give all vaccines to their at-risk populations, they must choose which diseases are most important to prevent through immunizations.
• Rates of disease — Because a disease may be an imminent threat in one place, but a minor threat elsewhere, different vaccines may be used routinely in different places. For example, because Japanese encephalitis virus (JEV) is not common in the U.S., it is not a routinely recommended vaccine. However, those who may be at risk of infection with JEV while traveling may be recommended to get the vaccine.

Why are different vaccines recommended for different people?

• Risks of disease — Some people are at a higher risk of developing a disease than others, so they are recommended to get particular vaccines. Increased risks may depend on where they live, underlying medical conditions, their age or race, or their social habits. Globally, immunization programs are typically aimed at infants and young children, who usually are at greatest risk of complication or death if infected.
• Risk of adverse events — Some people should not get specific vaccines because they are at an increased risk of having an adverse reaction. These risks may include medical conditions or allergies.

Why are vaccines given at different ages?

• Age of exposure — Social circumstances, such as crowding, nutrition, and the amount of disease circulating in a community determine when a child is most likely to be exposed to a potentially deadly infectious disease. As a result, advisory bodies must study these data to determine when it is best to give a particular vaccine in their country or area.
• Risk of complications or lack of immune response — Advisory bodies must also consider whether there is a potential risk of experiencing adverse events from or non-response to a vaccine due to age. This is balanced against the potential for exposure to determine the best time to give a vaccine.
• Feasibility — New vaccines may be given at a time when other vaccines are already recommended to reduce the number of visits needed and to streamline the administrative system. A vaccine that is going to be given with other vaccines must be tested with those vaccines to be sure there is no cross-reactivity or loss of effectiveness among them; these studies are called concomitant use studies.

Why are there differences in the number of doses given?

• Disease presence in the community — At the time that a vaccine is first introduced, the burden of disease in the community is typically high. As people are exposed to these natural infections, their protection against the disease is boosted; it is like getting another dose of the vaccine, except you don't know you were exposed to the pathogen.
  
  After the vaccine has been used for several years, there is likely to be less disease and, therefore, less chance for people to have their immunity boosted by natural infection. In some cases, this leads to the need for another dose of the vaccine, so that a person’s immunity is maintained.
• Vaccine differences — Vaccines are not the same worldwide. A vaccine against one disease may be made by several different companies and, therefore, consist of different types, parts or forms of the same bacteria or virus, or have different stabilizing or immune-enhancing agents.
• Supply and demand — When a vaccine is first given in a country, some governments require that a certain percentage of the population get the first dose of the vaccine before any additional doses can be given to individuals. This tends to happen in places where resources are limited.

The World Health Organization recommends the following vaccines for all children and adolescents:

• Pneumococcal
• Rotavirus
• Rubella
• Tuberculosis
• Polio
• Diphtheria
• Tetanus
• Pertussis
• Hepatitis B
• Measles
• Haemophilus influenzae type B
• Human papillomavirus

Several vaccines are recommended for some regions or populations. The WHO has several summary tables available for reference.

The WHO also offers a useful tool for vaccine schedules around the world. You can view information based upon country.