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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.

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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.

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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.

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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.

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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.

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The aim of the study reported here was to determine if bifurcated needles or multiple puncture cylinders would prove suitable for administration of measles vaccines. Children 9 to 11 months old in São Paulo, Brazil, were assigned to receive either Biken-Cam 70 (5,000 TCID50/0.5 ml) or Edmonston-Zagreb (7,000 TCID50/0.5 ml) measles vaccines intradermally with a bifurcated needle or a multiple puncture cylinder. These devices are usually used to administer smallpox or BCG vaccine. The volume of vaccine inoculated was approximately 0.003 ml. Measles IgG antibodies were measured by enzyme-linked immunosorbent assay (ELISA) at the time of vaccination and 8 weeks later. The study participants were examined 14 days after inoculation for possible adverse reactions. Overall, the children's average age was 9.5 +/- 0.66 months at vaccination. None of the 45 recipients of Biken-Cam vaccine responded serologically. The 49 Edmonston-Zagreb vaccine recipients immunized with the multiple puncture cylinder had a somewhat higher serologic response rate (35%) and mean concentration of measles antibodies (323 mIU/ml) than those 51 who received the same vaccine administered with the bifurcated needle (26% and 291 mIU/ml, respectively). The rates of reported symptoms after vaccination did not differ significantly among the groups. Overall, the low serologic response rates following intradermal immunization with for devices tested in this study indicate that this route of administration is not suitable for routine administration of standard-titer vaccines.

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The immunogenicity of trivalent oral poliovirus vaccine (TOPV), which is less effective in tropical than in temperate areas, may potentially be improved in several ways, including increasing the number of doses. Little information is available on TOPV when more than 6 doses are given. The situation in Cuba provides a unique opportunity to relate the seroprevalence of neutralizing antibodies to the dose of TOPV because Cuba has not reported culture-confirmed poliomyelitis since 1973 and TOPV is only administered in twice yearly 1-week mass immunization campaigns. Sera from 2000 children nationwide were studied for neutralizing antibody among children who received 0, 2, 4, 6 and 8 doses of TOPV. These doses were administered in the period 1989-91, when TOPV (from the USSR) was being used with 500,000, 200,000, and 300,000 median tissue-culture-infecting doses (TCID50) for types 1, 2 and 3, respectively--the 5:2:3 formulation. Seroprevalence of neutralizing antibody after two TOPV doses was 91.5% for type 1, 90.8% for type 2, and 45.9% for type 3. Seroprevalence of type-3 neutralizing antibody after 6 doses remained low (73.4%), but increased to 83.5% after 8 doses (P < 0.05). Although 16.5% of the children remained unprotected for type-3 infection even after 8 doses, mass campaign immunization strategies were sufficient to eradicate the transmission of wild poliovirus in Cuba. Because the seroprevalence of type-1 neutralizing antibody was high (91.5%) after two campaign doses, additional studies using different formulations are needed to determine whether simultaneous improvement in the type-3 response to two campaign doses can be achieved.

PIP: During December 1991-January 1992 in Cuba, health workers took blood samples from a nationwide sample of 2000 children aged 0-3 who received 0, 2, 4, 6, and 8 doses of trivalent oral poliovirus vaccine (TOPV) to determine the seroprevalence of poliovirus neutralizing antibodies for types 1, 2, and 3. Specifically, researchers wanted to learn whether TOPV becomes more effective as the number of doses increases. Since 1973, Cuba has conducted two mass immunization campaigns each year in February and April. During 1970-91, Cuba used a USSR-produced poliovirus vaccine that had 500,000, 200,000, and 300,000 median tissue-culture-infecting doses for types 1, 2, and 3, respectively. Wild poliovirus has not been transmitted in Cuba since 1973 (as of August 1993), indicating that the mass immunization campaigns without routine vaccine delivery have eradicated poliomyelitis in Cuba. The seroprevalence of poliovirus neutralizing antibodies for type 1 increased significantly between 2 and 4 doses (91.5% vs. 96.5%; p = 0.05), thereafter the increases were small and insignificant. The seroprevalence of poliovirus neutralizing antibodies for type 2 increased significantly between 2 and 4 doses (90.8% vs. 97.2%), with small insignificant increases thereafter. Two doses of TOPV induced a response against poliovirus type 3 in only 45.9% of cases. At 4 doses and 8 doses, it did increase significantly from the previous dose (71.2% and 83.5%, respectively; p 0.05). Further studies using other vaccine formulations would allow persons involved in global eradication efforts to determine whether two campaign doses can improve the immunogenicity of the type 3 poliovirus while also improving that of the type 1 poliovirus.

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Cartagena, Colombia, was one of the last cities in the Americas known to have endemic poliomyelitis. After 3 cases were identified in 1991, two approaches for detecting continued silent transmission of wild polioviruses within a high-risk community were used: stool surveys of healthy children and virologic analysis of community sewage. Wild type 1 polioviruses were isolated from 8% of the children studied and from 21% of sewage samples. The proportions of wild polioviruses, vaccine-related polioviruses, and nonpolio enteric viruses were similar for both approaches. Wild poliovirus sequences were also amplified directly from processed sewage samples by the polymerase chain reaction using primer pairs specific for the indigenous type 1 genotype. The last reported cases associated with wild polioviruses in the Americas occurred in Colombia (8 April 1991) and Peru (23 August 1991). Direct sampling for wild polioviruses in high-risk communities can provide further evidence that eradication of the indigenous wild polioviruses has been achieved in the Americas.

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In the span of 5 years since the eradication initiative was launched and only 3 years since external funds were made available, PAHO has been able to develop and implement a comprehensive program strategy for polio eradication that includes the following components: achievement and maintenance of high immunization levels (which include the supplemental strategies of national immunization days and mop-up operations); effective surveillance to detect all new cases; and a rapid response to the occurrence of new cases. Despite yearly increases in the number of cases of acute flaccid paralysis reported to the surveillance system, a decline in reported confirmed cases of polio has occurred since 1986 to record low levels in 1989. Cases in 1989 were reported from only 0.7% of the counties in the Americas. The occurrence of 24 wild-type virus isolates in 1989 were limited to only three geographic areas: northwestern Mexico; the northern Andean Region; and northeastern Brazil. At this writing the clock is ticking with only 3 months left to achieve the goal of interrupting transmission by the end of 1990. If the current level of effort is sustained and special efforts are directed at the remaining foci of infection, the eradication of the transmission of wild-type poliovirus from the Americas can be achieved. Continued external financial support will be critical if the effort is to succeed. The prospect of poliomyelitis eradication in the Americas led the 41st World Health Assembly of WHO to adopt a resolution in May, 1988, to eradicate the indigenous transmission of wild-type poliovirus from the world by the year 2000.(ABSTRACT TRUNCATED AT 250 WORDS)

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