Is global measles eradication feasible?

Measles is one of most infectious diseases. Before the introduction of the measles vaccine, practically all children in the long run contracted measles. By the end of the 1980s most countries of the world had incorporated measles vaccine into their routine vaccination programs. Globally, some 800,000 deaths due to measles still occur every year, half of them in Africa. Eradication of measles would play an important role in improving child survival. The goal to eradicate measles from the Americas was set by the Pan American Sanitary Conference in 1994. Progress to date has been remarkable. Measles is no longer an endemic disease in the Americas and interruption of transmission has been documented in most countries. As of August 2005, 3 years have elapsed since the detection of the last indigenous case in Venezuela in September 2002. This experience shows that interruption of measles transmission can be achieved and sustained over a long period of time and that global eradication is feasible if appropriate strategy is implemented. Even in a new paradigm in which eradication is not followed by the discontinuation of vaccination, eradication of measles will be a good investment to avoid expensive epidemics and save the almost one million children that die every year to infection with the measles virus. It is not a dream to think that we will se a world free of measles by the year 2015.

Persistence of vaccine-derived poliovirus following a mass vaccination campaign in Cuba: implications for stopping polio vaccination after global eradication.

BACKGROUND: With substantial progress made toward polio eradication, developing the appropriate strategy for discontinuing global oral poliovirus vaccine (OPV) after global eradication becomes increasingly important. At issue is the theoretical risk of independent circulation of potentially virulent OPV-derived strains. Because Cuba uses OPV only in mass campaigns, it represents an ideal site to assess vaccine-derived poliovirus persistence. METHODS: Infants born after the 1997 biannual mass campaigns were evaluated for past (neutralizing antibody) or current (virus excretion) evidence of vaccine-derived poliovirus exposure. We obtained sera and/or stool specimens from 861 infants; a second serum from 218 infants. RESULTS: All stool specimens were poliovirus negative. Of 762 infants, 113 (14.8%) had initially detectable poliovirus type 1 antibody, 193 (25.3%) type 2, and 94 (12.3%) type 3. A precipitous antibody decline occurred in initially positive sera. CONCLUSIONS: Our results suggest that in a country with high population immunity, vaccine-derived virus is unlikely to establish ongoing circulation.

[Poliomyelitis outbreak caused by vaccine-derived virus in Haiti and the Dominican Republic]. / Brote de poliomielitis en Haití y la República Dominicana debido a un virus derivado de la vacuna antipoliomielítica oral.

In October 2000, the Ministries of Health of the Dominican Republic and Haiti notified two cases of acute flaccid paralysis (AFP) in rural areas, one of them in a 9-month-old female, and the other in a 2-year-old female, respectively. Stool samples that were obtained from these cases, which occurred in July and August 2000, after a 9-year interruption of wild poliovirus circulation in the Western Hemisphere, revealed the presence of type 1 poliovirus. Genetic sequencing, which was later performed at the Centers for Disease Control and Prevention, in Atlanta, Georgia, United States of America, revealed an atypical descendant of the virus used in the manufacture of the oral polio vaccine (OPV), but with 3% genetic divergence with respect to the parent strain. Normally, viral isolates that derive from vaccine components show 99.5% genetic agreement with the parent strain; in wild polioviruses, on the other hand, this agreement is usually less than 82.0%. Thus, the 3% genetic divergence detected in this study suggests that, in areas with low vaccine coverage, the virus used in the vaccine remained in circulation for at least two years, during which it recovered the neurovirulence and communicability of wild poliovirus type 1. This report describes the characteristics and results of the active search for cases of AFP that was sparked by the detection of the two index cases. It also looks at the public health implications of this outbreak for the entire Region of the Americas.

Strategies to eradicate rubella in the English-speaking Caribbean.

OBJECTIVE: This report presents the strategies used to eradicate rubella in the Caribbean region and the challenges faced by that effort. METHODS: Using the surveillance system for measles cases that was instituted in all countries in the Caribbean Community (CARICOM), 12 countries confirmed cases of rubella between 1992 and 1996. Rubella infections occurred in epidemic proportions in 6 countries during that period. RESULTS: On the basis of the rubella prevalence data, rubella-congenital rubella syndrome (CRS) cost-benefit analysis, and cost-effectiveness of the mass campaign, the Council for Human and Social Development of CARICOM resolved, on April 21, 1998, that every effort would be made to eradicate rubella, as well as to prevent the occurrence of new cases of CRS by the end of 2000. Using the Pan American Health Organization's template for measles eradication, CARICOM proposed and implemented the main strategies for rubella and CRS eradication, and rubella mass campaigns were conducted in 18 countries. The target population, which included males and females (aged 20-40 years), was approximately 2.2 million. CONCLUSION: The major challenges for rubella eradication are attaining high vaccine coverage in the adult population and maintaining an effective surveillance system able to detect rubella activity.

Review of regional measles surveillance data in the Americas, 1996-99.

BACKGROUND: In 1994, ministers of health of countries of North and South America established the goal of measles eradication from the western hemisphere by 2000. To accomplish this goal, the Pan American Health Organization (PAHO) developed an enhanced measles vaccination strategy. METHODS: PAHO's measles eradication vaccination strategy has evolved into three principal components; a catch-up measles vaccination campaign, maintenance of high vaccination coverage (keep-up), and periodic follow-up measles vaccination campaigns. To monitor progress towards measles eradication, measles surveillance has been strengthened, including the laboratory investigation of suspected measles cases. FINDINGS: Both the catch-up and follow-up mass campaigns achieved high vaccination coverages in the respective targeted age groups. In 1996, only 2109 confirmed measles cases were reported in the Americas. In 1997, there was a resurgence of measles in the Americas, mostly as a result of a large measles outbreak with over 42000 cases, which occurred mainly among unvaccinated young adults in Sao Paulo State, Brazil. By 1998, there was a reduction in the number of reported confirmed measles cases, with a total of 14474 cases. Reduction of cases continued to the end of 1999, with a total of only 2828 confirmed cases. INTERPRETATION: PAHO's measles eradication strategy has been effective in interrupting transmission and maintaining the absence of measles virus circulation in most parts of the Americas. The PAHO experience provides strong evidence that with full implementation of an appropriate vaccination strategy, measles transmission can be effectively interrupted.

State of immunization in the Americas.

Countries in the Americas have led the world in conquering infectious diseases preventable through vaccination. In 1971, the Western hemisphere achieved smallpox eradication. In 1991, the Americas were free of indigenous transmission of wild poliovirus. In 1998, overall regional vaccination coverage was 86% for diphtheria-pertussis-tetanus, 89% for oral poliovirus vaccine 3, 98% for bacille Calmette-Guérin vaccine, and 85% for measles. These figures confirm that most of the children in the Americas are protected against these diseases. The breakthroughs obtained in immunization have stimulated countries to promote new initiatives aimed at the control and eradication of other vaccine-preventable diseases and to introduce new vaccines into routine schedules. In the 21st century, vaccines will remain the most cost-effective means of preventing diseases and avoiding expensive treatment costs.

Rational use of rubella vaccine for prevention of congenital rubella syndrome in the Americas.

Rubella is a viral disease with minor morbidity and few complication unless it is contracted by a pregnant woman. Rubella infection during the first trimester of pregnancy often leads to fetal death or severe congenital defects (congenital rubella syndrome, CRS). Rubella remains endemic in many countries of Latin America and the Caribbean. It has been estimated that 20,000 or more infants are perhaps born with CRS each year in Latin American and Caribbean countries. While the inclusion of rubella vaccination into routine childhood immunization will decrease rubella virus circulation among young children, it will not have immediate impact on the transmission of rubella among adults or the occurrence of CRS. A one-time mass campaign targeting both males and females 5 to 39 years of age with measles-mumps-rubella or measles-rubella vaccine followed by the use of measles-mumps-rubella vaccine in routine early childhood vaccination will prevent and control both rubella and CRS promptly. In April 1988, the Ministers of Health of the English-speaking Caribbean targeted rubella for elimination by the end of the year 2000 using the vaccination strategy outlined above. The rubella elimination experience of these countries will provide useful information for the eventual elimination of rubella virus from the Americas.

[Eradication of measles in Cuba]. / La eliminación del sarampión en Cuba.

The vaccine against measles came into use in Cuba in 1971. During the seventies, a new early strategy for measles control was established, and it was followed by further efforts in the early eighties. Despite improvements to the control program, disease outbreaks continued to occur. In 1986, after examining the experience acquired through the control initiatives that were already in place, a new measles vaccination strategy was adopted. In time, the new vaccination strategy against measles came to have three main components: first, a single vaccination "catching-up" campaign targeting children 1 to 14 years of age. Second, efforts were made to achieve and maintain high vaccine coverage through mandatory vaccination services for 12-month-old children ("maintenance vaccination"). Finally, periodic "follow-up" campaigns were carried out for children 2 to 6 years of age. Steps were taken, for the purpose of monitoring the progress made so far toward eliminating measles, to strengthen disease surveillance systems, including the screening of suspected cases. The "catching-up" and "follow-up" campaigns both achieved greater than 98% coverage within targeted age groups. The routine vaccination program has also maintained high coverage. The high population immunity against measles that has been attained through these vaccination strategies has resulted in a rapid decrease in the incidence of the disease. From 1989 to 1992, less than 20 laboratory-confirmed cases were reported annually. In Cuba, the last case confirmed through serologic screening was reported in July 1993. Cuba's strategy for measles elimination has interrupted disease transmission and kept the causal virus from circulating on the island. Cuba's experience with measles elimination suggests that if an appropriate vaccination strategy is applied, measles can be globally eradicated.

Measles eradication: experience in the Americas.

In 1994, the Ministers of Health from the Region of the Americas targeted measles for eradication from the Western Hemisphere by the year 2000. To achieve this goal, the Pan American Health Organization (PAHO) developed an enhanced measles eradication strategy. First, a one-time-only "catch-up" measles vaccination campaign is conducted among children aged 9 months to 14 years. Efforts are then made to vaccinate through routine health services ("keep-up") at least 95% of each newborn cohort at 12 months of age. Finally, to assure high population immunity among preschool-aged children, indiscriminate "follow-up" measles vaccination campaigns are conducted approximately every 4 years. These vaccination activities are accompanied by improvements in measles surveillance, including the laboratory testing of suspected measles cases. The implementation of the PAHO strategy has resulted in a marked reduction in measles incidence in all countries of the Americas. Indeed, in 1996 the all-time regional record low of 2109 measles cases was reported. There was a relative resurgence of measles in 1997 with over 20,000 cases, due to a large measles outbreak among infants, preschool-aged children and young adults in São Paulo, Brazil. Contributing factors for this outbreak included: low routine infant vaccination coverage, failure to conduct a "follow-up" campaign, presence of susceptible young adults, and the importation of measles virus, apparently from Europe. PAHO's strategy has been effective in interrupting measles virus circulation. This experience demonstrates that global measles eradication is an achievable goal using currently available measles vaccines.

Eradication of wild poliovirus from the Americas: wild poliovirus surveillance--laboratory issues.

The Pan American Regional Poliomyelitis Laboratory Network, developed to support the program to eradicate indigenous wild poliovirus transmission in the Americas, included 10 laboratories, distributed in eight countries in the Americas, organized according to the diagnostic procedures they regularly performed. All laboratories isolated and typed virus in stool specimens, several did intratypic differentiation by nucleic acid probe hybridization, and 2 sequenced wild poliovirus isolates for molecular epidemiologic studies. High performance of the network was maintained through comprehensive training of virologists, continuous monitoring of laboratory performance, and prompt investigation of problems. Recommended field and laboratory procedures were regularly reviewed and revised to optimize sensitivity, specificity, and diagnostic efficiency. Close integration of field and laboratory surveillance was achieved through frequent meetings between virologists and epidemiologists, effective communication of program priorities, and the distribution of weekly surveillance reports.

Eradication of wild poliovirus from the Americas: acute flaccid paralysis surveillance, 1988-1995.

In May 1985, the Pan American Health Organization proposed the goal of interruption of wild poliovirus transmission in the Western Hemisphere. An important component of the polio eradication strategy was conducting surveillance for cases of acute flaccid paralysis. Reported cases were thoroughly investigated, including the collection of stool samples for testing for the presence of wild poliovirus. The last patient with poliomyelitis due to wild poliovirus in the Americas had onset of paralysis on 23 August 1991 in Peru. Since then, >9000 cases of acute flaccid paralysis have been reported and thoroughly investigated; none has been confirmed as paralytic poliomyelitis due to wild poliovirus. On 29 September 1994, the International Commission for the Certification of Poliomyelitis Eradication declared the Americas to be polio-free.

Epidemiologic study of Guillain-Barré syndrome in children <15 years of age in Latin America.

In 1986, surveillance of acute flaccid paralysis (AFP) cases among children <15 years of age was implemented in Latin America as part of the initiative to eradicate poliomyelitis from the Western Hemisphere. Data on AFP, including Guillain-Barré syndrome (GBS), could be analyzed from a regional registry system and from specific GBS studies in seven countries. Between 1989 and 1991, 3112 cases of GBS were reported in Latin America, representing 52% of all nonpolio AFP cases. From the studies in seven countries, a total of 1527 GBS cases (49%) were studied, representing an overall annual incidence rate of 0.91/100,000 children <15 years old. Follow-up investigations showed a persistent muscular weakness at 60 days, 6 months, and 1 year after onset in 61%, 14%, and 10% of children, respectively. This study confirms that with the disappearance of polio, GBS arises as the most common cause of AFP.

National immunization days: experience in Latin America.

Organization of national immunization days (NIDs) in all countries in Latin America in which polio was endemic has been one of the key elements that led to the interruption of the circulation of the wild poliovirus in 1991 from the Americas. National initiatives for control or elimination of measles using similar strategies have emerged from the successful organization of NIDs for polio eradication and lead the way to the eventual global eradication of this major killer of children. The major reasons for the success of polio eradication in the Americas were the commitment of national authorities, well-defined strategies, sustainable effort, and the participation of all sectors of society.

Certification of the eradication of indigenous transmission of wild poliovirus in the Americas.

In May 1985, the Pan American Health Organization launched an initiative to interrupt indigenous transmission of the wild poliovirus from the Western Hemisphere by the year 1990. The strategy to achieve this goal was based on the maintenance of high levels of immunity in the population at risk and the establishment of a surveillance system to detect polio cases and respond promptly with control measures. On 23 August 1991, a 2-year-old boy with acute flaccid paralysis due to wild poliovirus was detected in Junin, Peru, the last isolation of such a virus in the entire Western Hemisphere. In 1990, an International Commission for the Certification of Eradication of Poliomyelitis Eradication (ICCPE) was established by the Pan American Health Organization to eventually determine if transmission was interrupted. After 3 years of follow-up and review of surveillance data, the ICCPE declared that wild poliovirus transmission had been interrupted in the Americas.

Measles vaccination and Guillain-Barré syndrome.

BACKGROUND: Guillain-Barré syndrome (GBS) has been associated with several infectious agents, and the possibility that the disorder may be caused by vaccination has been raised. We compared the numbers of cases of GBS observed immediately after mass measles vaccination campaigns with the numbers that would be expected from baseline rates, to assess whether there is a causal relation between measles vaccination and GBS. METHODS: We analysed data on 2296 cases of GBS reported to the Poliomyelitis Eradication Surveillance System of the Pan American Health Organization as cases of suspected poliomyelitis. These cases occurred among 73 million immunised children aged 9 months to 15 years in Argentina, Brazil, Chile, and Colombia, between January, 1990, and December, 1994. These children were targeted for mass measles vaccination campaigns (each lasting 1 month) in 1992 and 1993. The frequency of GBS cases observed during the vaccination campaigns or the next 42 days (the latent period) was compared with that during the rest of the study period, with the assumption of a Poisson distribution. FINDINGS: The average annual incidence of GBS was 0.62 per 100000 children aged 1-14 years. The number of cases that would be expected within any 72-day period would therefore be 92. The average observed number of cases during latent periods after measles vaccination was 97. The probability that 97 or more cases would occur during a period with an expected number of 92 was 0.31. INTERPRETATION: The average annual rates of GBS by age-group for the 5 years analysed were consistent with previous data; thus we are confident that the surveillance system is sufficiently sensitive. There was no statistically significant association between measles vaccination and GBS. If there is any causal relation, the number of GBS cases due to measles vaccination was so small that data from the vaccination of more than 70 million children were not sufficient to detect a rise in the number of observed GBS cases beyond the expected number.

Measles elimination in the Americas. Evolving strategies.

The strategy currently used to control measles in most countries has been to immunize each successive birth cohort through the routine health services delivery system. While measles vaccine coverage has increased markedly, significant measles outbreaks have continued to recur. During the past 5 years, experience in the Americas suggests that measles transmission has been interrupted in a number of countries (Cuba, Chile, and countries in the English-speaking Caribbean and successfully controlled in all remaining countries. Since 1991 these countries have implemented one-time "catch-up" vaccination campaigns (conducted during a short period, usually 1 week to 1 month, and targeting all children 9 months through 14 years of age, regardless of previous vaccination status or measles disease history). These campaigns have been followed by improvements in routine vaccination services and in surveillance systems, so that the progress of the measles elimination efforts can be sustained and monitored. Follow-up mass vaccination campaigns for children younger than 5 years are planned to take place every 3 to 5 years.