Vaccine-preventable diseases


Information on vaccine-preventable diseases

About Hepatitis Vaccine

Hepatitis is an acute, usually self-limiting, disease of the liver caused by the hepatitis virus. The hepatitis A virus (HAV) is transmitted from person to person, primarily by the fecal-oral route, and is closely associated with poor sanitary conditions. The most common modes of transmission include close personal contact with an infected person and ingestion of contaminated food and water.

The virus occurs worldwide and causes about 1.5 million cases of clinical hepatitis each year. Humans are the only reservoir of HAV.

Millions of persons have now been vaccinated against HAV. The current vaccines are well tolerated and no serious adverse events have been statistically linked to their use. Contraindications to hepatitis A vaccination include a known allergy to any of the vaccine components. Hepatitis A vaccine may be administered with all other vaccines included in the Expanded Program on Immunization and with vaccines commonly given for travel. None of the vaccines are licensed for children aged 1 year.

Planning for large-scale immunization programs against hepatitis A should involve careful analyses of cost-benefit and sustainability of different appropriate hepatitis A prevention strategies, as well as an assessment of the possible long-term epidemiological implications of vaccination at different levels of coverage.

Please visit our section Knowledge Resources for Hepatitis for more information.

About the influenza vaccine

The main purpose of seasonal influenza vaccination is to avoid severe disease from infection with influenza virus. Currently, 39 countries and territories in the Americas offer influenza vaccination to nationally-defined high-risk groups.

PAHO's Technical Advisory Group on Vaccine-Preventable Diseases (TAG) recommends that the following groups of individuals may be targeted for vaccination in order to reduce the incidence of severe illness and premature death: pregnant women, children between 6 months to 5 years, elderly individuals, individuals with chronic medical conditions, and healthcare workers. Because of the vulnerability of pregnant women to complications from influenza infection, TAG urges countries to increase vaccine uptake of pregnant women. Influenza vaccination in pregnancy is considered safe and is recommended for all women at any stage of pregnancy during the influenza season. This recommendation is motivated not only by the potential severe course of influenza during pregnancy, but also in order to protect infants against influenza during their vulnerable first six months of life.

Influenza vaccine is available in two preparations, Trivalent or Quadrivalent Inactivated Influenza Vaccine (TIV or QIV) and Live, Attenuated Influenza Vaccine (LAIV). TIV and LAIV are antigenically equivalent and contain three annually-recom¬mended influenza strains—two subtypes of influenza A (H3N2), influenza A (H1N1), and one subtype of influenza B. QIV contains these three plus an additional subtype of influenza B. Each year, the influenza viruses to be included in the vaccine are assessed on the basis of global surveillance for influenza viruses.

Please visit our section Knowledge Resources for Influenza for more information.

About Measles

Measles is a highly contagious viral disease, which affects mostly children. It is transmitted via droplets from the nose, mouth, or throat of infected persons. Initial symptoms, which usually appear 10—12 days after infection, include high fever, runny nose, bloodshot eyes, and tiny white spots on the inside of the mouth. Several days later, a rash develops, starting on the face and upper neck and gradually spreading downwards. There is no specific treatment for measles and most people recover within 2—3 weeks. However, particularly in malnourished children and people with reduced immunity, measles can cause serious complications, including blindness, encephalitis, severe diarrhea, ear infection, and pneumonia. Measles can be prevented by immunization. Source: WHO.

About Poliomyelitis

Poliomyelitis (polio) is a highly infectious viral disease, which mainly affects young children. The virus is transmitted through contaminated food and water, and multiplies in the intestine, from where it can invade the nervous system. 
Many infected people have no symptoms, but do excrete the virus in their faeces, hence transmitting infection to others. Initial symptoms of polio include fever, fatigue, headache, vomiting, stiffness in the neck, and pain in the limbs.
In a small proportion of cases, the disease causes paralysis, which is often permanent. Polio can only be prevented by immunization.

About Rotavirus

Disease Burden

Infection from rotavirus is the most common cause of diarrhea among children under five years old worldwide.

In 2003, it was estimated that between 1986 and 2000, rotavirus caused 111 million episodes of infantile diarrhea each year, strictly requiring at-home care, 25 million medical visits, two million hospitalizations, and an average of 440,000 deaths worldwide. This means that by five years of age, almost all children have experienced an episode of rotavirus diarrhea: one out of five children has been given a medical consultation; one out of 65 has been hospitalized, and one out of about 293 has died.

Another study estimates that from 2000-2004, child deaths from rotavirus rose to 600,000 or more around the world.

Globally, diarrhea from rotavirus A (RVA) in 2008 resulted in 453,000 deaths among children under five, comprising 37% of deaths attributable to diarrhea and 5% of all deaths in children <5 years.

More recently, it was estimated that RVA caused approximately 197,000 deaths in 2011, which means that it is still the most important cause of diarrhea-related mortality worldwide.

It was estimated for 14 countries in Latin America that RVA caused 6,302 deaths and 229,656 hospitalizations annually in the absence of RVA vaccination.

While the incidence of rotavirus infection in developed and developing countries is similar, 80% of deaths occur in developing countries.

About Rubella

Rubella is a contagious viral disease, which occurs most often in children. The virus is transmitted via the respiratory route, and symptoms usually appear 2-3 weeks after exposure. In children, the disease is usually mild, with low fever, nausea and a transient rash. Adults may develop arthritis and painful joints. Infection during early pregnancy may cause fetal death or congenital rubella syndrome, which is characterized by multiple defects, particularly to the brain, heart, eyes and ears. There is no specific treatment for rubella. The disease can be prevented by immunization.

Factsheet 2015:   pdfElimination of rubella and congenital rubella syndrome in the Americas

About Yellow Fever Vaccine

Yellow fever is a zoonosis indigenous to some tropical regions of South America and Africa which has caused numerous epidemics with high mortality rates throughout history. Its etiologic agent is the yellow fever virus, an arbovirus of the genus Flavivirus (family Flaviviridae). Transmission occurs through the bite of certain species of mosquitoes: In jungle areas of South America, by mosquitoes of the Haemagogus and Sabethes genera. In urban and certain rural areas, the bite of infective Aedes aegypti mosquitoes.

Yellow fever can be prevented with live-attenuated yellow fever vaccine 17D, which is considered safe and effective, and has been used for over 60 years to actively immunize children and adults against infection with the yellow fever virus. It confers lasting immunity, perhaps for life.

Yellow fever vaccination strategies implemented in the Region of the Americas include: 1) introduction of yellow fever vaccine into national immunization programs in all endemic countries for children aged 1 year; 2) vaccination campaigns during inter-epidemic periods; 3) vaccination campaigns in response to outbreaks or epizootics; and 4) vaccination of travelers entering enzootic areas, except when contraindicated.

It is recommended that the yellow fever vaccine be administered at 12 months of age. In the case of outbreaks, it can be administered as early as 6 months of age.

Please visit our section Knowledge Resources for Yellow Fever for more information.