Immunogenicity of measles and rubella vaccines in Oman: a prospective clinical trial.

A prospective immunogenicity trial of measles and rubella vaccines was conducted in Oman. Children received measles vaccine at age 9 months and measles-rubella vaccine at age 15 months. Serum specimens were tested for measles-specific IgG and rubella-specific IgG. Of 1025 eligible infants, 881 (86.0%) returned for all five visits and had adequate serum samples for testing. Seroconversion to measles after vaccination at 9 months was 98.1%. At 15 months, 47 (5.3%) of the 881 children were seronegative for measles; of these, 44 (93.6%) seroconverted. At 16 months, 99% of the children seronegative at age 9 months seroconverted after receiving two doses of measles vaccine. At age 15 months, 684 (77.6%) children were seronegative for rubella. Of these, 676 (98.8%) seroconverted by age 16 months. One dose of measles vaccine at age 9 months was highly immunogenic. One dose of measles-rubella vaccine at age 15 months closed the remaining measles immunogenicity gap and resulted in a high rate of rubella seroconversion.

Outbreak of poliomyelitis due to type 3 poliovirus, northern India, 1999-2000: injections a major contributing factor.

BACKGROUND: A large outbreak of poliomyelitis due to poliovirus type 3 (P3) occurred in India in 1999. This raised concerns about oral poliovirus vaccine (OPV) effectiveness, particularly the type 3 component, in preventing clinical disease and offered an opportunity to describe the epidemiology of a P3 outbreak. METHODS: We reviewed data collected by the National Polio Surveillance Project to describe the outbreak and conducted a case-control study to determine risk factors for the development of paralytic poliomyelitis. The P3 cases with paralysis onset in 2000 were enrolled with four controls per case, matched for age and neighbourhood. RESULTS: Of 1126 virologically confirmed poliomyelitis cases reported in 1999, 719 (64%) were due to P3. We enrolled 48 (80%) of 60 cases and 175 matched controls. Age (30.6 months, cases versus 30.4 months, controls) and vaccination status (median 5.8 OPV doses, cases versus 6.1 OPV doses, controls) were similar among cases and controls. The only significant difference between the groups was the proportion that received any injection in the last 30 days prior to paralysis onset or the corresponding reference date for controls (35.4% versus 12.3%, adjusted odds ratio [OR] = 3.9, 95% CI: 1.8-12.5). CONCLUSIONS: Cases and controls had similar vaccination histories. The only significant risk factor for paralytic illness was having received any injection in the 30 days before onset. Our study confirms that injections administered during the poliovirus incubation period can provoke paralytic poliomyelitis. Injections in polio-endemic countries should only be indicated when other therapeutic options have failed or are not available.

Compatible poliomyelitis cases in India during 2000.

OBJECTIVE: To describe the characteristics of compatible poliomyelitis cases and to assess the programmatic implications of clusters of such cases in India. METHODS: We described the characteristics of compatible poliomyelitis cases, identified clusters of compatible cases (two or more in the same district or neighbouring districts within two months), and examined their relationship to wild poliovirus cases. FINDINGS: There were 362 compatible cases in 2000. The incidence of compatible cases was higher in districts with laboratory-confirmed poliomyelitis cases than in districts without laboratory-confirmed cases. Of 580 districts, 96 reported one compatible case and 72 reported two or more compatible cases. Among these 168 districts with at least one compatible case, 123 had internal or cross- border clusters of compatible cases. In 27 districts with clusters of compatible cases, no wild poliovirus was isolated either in the same district or in neighbouring districts. Three of these 27 districts presented laboratory-confirmed poliomyelitis cases during 2001. CONCLUSION: Most clusters of compatible cases occurred in districts identified as areas with continuing wild poliovirus transmission and where mopping-up vaccination campaigns were carried out. As certification nears, areas with compatible poliomyelitis cases should be investigated and deficiencies in surveillance should be corrected in order to ensure that certification is justified.

Predictors of virologically confirmed poliomyelitis in India, 1998-2000.

As we progress toward eradication of polio, a growing proportion of cases of acute flaccid paralysis (AFP) reported are due to causes other than polio. AFP surveillance data from India for 1998-2000 were analyzed to determine the sensitivity and specificity of signs and symptoms present at initial case investigation and of residual weakness (which is used to classify AFP cases) for virologically confirmed poliomyelitis. Sensitivity was highest for age of <5 years (93%-97%) and residual weakness (74%-96%). Residual weakness was more sensitive among children aged <5 years. Cases of AFP in patients aged <5 years who have fever and asymmetrical paralysis are most likely to be confirmed as poliomyelitis. In countries with suboptimal surveillance for AFP, these results may help to prioritize investigation of AFP cases. The high sensitivity of residual weakness demonstrates the importance of 60-day follow-up examination for all patients with AFP, particularly those for whom the initial case investigation was inadequate or delayed.

Vaccine-associated paralytic poliomyelitis in India during 1999: decreased risk despite massive use of oral polio vaccine.

OBJECTIVE: Vaccine-associated paralytic poliomyelitis (VAPP) is a rare but serious consequence of the administration of oral polio vaccine (OPV). Intensified OPV administration has reduced wild poliovirus transmission in India but VAPP is becoming a matter of concern. METHODS: We analysed acute flaccid paralysis (AFP) surveillance data in order to estimate the VAPP risk in this country. VAPP was defined as occurring in AFP cases with onset of paralysis in 1999, residual weakness 60 days after onset, and isolation of vaccine-related poliovirus. Recipient VAPP cases were a subset with onset of paralysis between 4 and 40 days after receipt of OPV. FINDINGS: A total of 181 AFP cases met the case definition. The following estimates of VAPP risk were made: overall risk, 1 case per 4.1 to 4.6 million OPV doses administered; recipient risk,1 case per 12.2 million; first-dose recipient risk, 1 case per 2.8 million; and subsequent-dose recipient risk, 1 case per 13.9 million. CONCLUSION: On the basis of data from a highly sensitive surveillance system the estimated VAPP risk in India is evidently lower than that in other countries, notwithstanding the administration of multiple OPV doses to children in mass immunization campaigns.