Measles: The Need for 2 Opportunities for Prevention

Characterizing measles transmission in India: a dynamic modeling study using verbal autopsy data

BACKGROUND

Decreasing trends in measles mortality have been reported in recent years. However, such estimates of measles mortality have depended heavily on assumed regional measles case fatality risks (CFRs) and made little use of mortality data from low- and middle-income countries in general and India, the country with the highest measles burden globally, in particular.

METHODS

We constructed a dynamic model of measles transmission in India with parameters that were empirically inferred using spectral analysis from a time series of measles mortality extracted from the Million Death Study, an ongoing longitudinal study recording deaths across 2.4 million Indian households and attributing causes of death using verbal autopsy. The model was then used to estimate the measles CFR, the number of measles deaths, and the impact of vaccination in 2000-2015 among under-five children in India and in the states of Bihar and Uttar Pradesh (UP), two states with large populations and the highest numbers of measles deaths in India.

RESULTS

We obtained the following estimated CFRs among under-five children for the year 2005: 0.63% (95% confidence interval (CI): 0.40-1.00%) for India as a whole, 0.62% (0.38-1.00%) for Bihar, and 1.19% (0.80-1.75%) for UP. During 2000-2015, we estimated that 607,000 (95% CI: 383,000-958,000) under-five deaths attributed to measles occurred in India as a whole. If no routine vaccination or supplemental immunization activities had occurred from 2000 to 2015, an additional 1.6 (1.0-2.6) million deaths for under-five children would have occurred across India.

CONCLUSIONS

We developed a data- and model-driven estimation of the historical measles dynamics, CFR, and vaccination impact in India, extracting the periodicity of epidemics using spectral and coherence analysis, which allowed us to infer key parameters driving measles transmission dynamics and mortality.

Controlling measles using supplemental immunization activities: a mathematical model to inform optimal policy

BACKGROUND

The Measles & Rubella Initiative, a broad consortium of global health agencies, has provided support to measles-burdened countries, focusing on sustaining high coverage of routine immunization of children and supplementing it with a second dose opportunity for measles vaccine through supplemental immunization activities (SIAs). We estimate optimal scheduling of SIAs in countries with the highest measles burden.

METHODS

We develop an age-stratified dynamic compartmental model of measles transmission. We explore the frequency of SIAs in order to achieve measles control in selected countries and two Indian states with high measles burden. Specifically, we compute the maximum allowable time period between two consecutive SIAs to achieve measles control.

RESULTS

Our analysis indicates that a single SIA will not control measles transmission in any of the countries with high measles burden. However, regular SIAs at high coverage levels are a viable strategy to prevent measles outbreaks. The periodicity of SIAs differs between countries and even within a single country, and is determined by population demographics and existing routine immunization coverage.

CONCLUSIONS

Our analysis can guide country policymakers deciding on the optimal scheduling of SIA campaigns and the best combination of routine and SIA vaccination to control measles.

Measles-mumps-rubella revaccination; 18 months vs. 4-6 years of age: potential impacts of schedule changes

OBJECTIVE

The policy of administering the second dose of measles-mumps-rubella (MMR) vaccine (MMR(2)) has recently changed in Iran, at age 1.5 years instead of 4-6 years previously. The effects of such a change on the immune status of the individual are evaluated in this study.

METHODS

Totally 249 and 228 children aged 18 months and 4- to 6-year-olds, respectively, with a documented receipt of primary MMR vaccine at the age of ≥ 1 year were enrolled. Before, and 4-6 weeks after MMR(2) administration, anti-MMR IgG antibody levels were measured using ELISA method. IgM antibody levels were also assessed in measles-rubella seronegative children that responded to MMR(2). Collected data for each component from both age groups were compared by using Fischer's exact probability and chi-square tests.

RESULTS

Before revaccination, measles seroimmunity rate was similar between the two groups, but rates to mumps and rubella were significantly higher in younger children-measles: 74 vs. 78.3%; mumps: 82.3 vs. 68.4% and rubella: 75% vs. 67%, respectively. After administration of MMR(2), all seroimmune subjects were IgG boosted. Except for rubella, older seronegative children showed significantly higher seroconvertion rate to MMR(2) and seroprevalence rates increased in vaccinees--measles: 98.2 vs. 94%, mumps: 97 vs. 94.4% and rubella: 87 vs. 92.4%, respectively. Only few measles-rubella seronegative children showed IgM response to MMR(2).

CONCLUSION

This study showed that the majority of younger children were susceptible to MMR infection before revaccination. Earlier age policy provides more protection against MMR in preschool-aged children. Rubella strain seems to be less potent than reported.

Measles: old vaccines, new vaccines

Isolation of measles virus in tissue culture by Enders and colleagues in the 1960s led to the development of the first measles vaccines. An inactivated vaccine provided only short-term protection and induced poor T cell responses and antibody that did not undergo affinity maturation. The response to this vaccine primed for atypical measles, a more severe form of measles, and was withdrawn. A live attenuated virus vaccine has been highly successful in protection from measles and in elimination of endemic measles virus transmission with the use of two doses. This vaccine is administered by injection between 9 and 15 months of age. Measles control would be facilitated if infants could be immunized at a younger age, if the vaccine were thermostable, and if delivery did not require a needle and syringe. To these ends, new vaccines are under development using macaques as an animal model and various combinations of the H, F, and N viral proteins. Promising studies have been reported using DNA vaccines, subunit vaccines, and virus-vectored vaccines.

Measles in travelers: are we aware enough?

Measles is still an important public health concern in most developing countries. Nonimmune or single-dose vaccinees traveling to high-endemic countries should be advised on the risk of acquiring the infection. We describe two cases of imported measles in Spanish travelers.

Long-term persistence of antibodies after one or two doses of MMR-vaccine

Outbreaks of measles, mumps and rubella have occurred recently despite long-standing mass immunization with MMR. Antibody titres for measles, mumps and rubella of 160 students (17-23 years) with proof of at least one MMR-vaccine were studied according to the number of MMR-vaccines received. The proportion of subjects with positive antibody titres was significantly higher in those who received two vaccines against measles (77.1% versus 58.7%, p=0.05), mumps (67.5% versus 55.6%, p=0.009) and rubella (99.2% versus 71.4%, p=0.008). Comparable significant trends were seen for GMTs for measles and mumps. A similar non-significant trend was noted for rubella.

Infection of cynomolgus macaques (Macaca fascicularis) and rhesus macaques (Macaca mulatta) with different wild-type measles viruses

Both rhesus and cynomolgus macaques have been used as animal models for measles vaccination and immunopathogenesis studies. A number of studies have suggested that experimental measles virus (MV) infection induces more-characteristic clinical features in rhesus than in cynomolgus monkeys. In the present study, both macaque species were infected with two different wild-type MV strains and clinical, virological and immunological parameters were compared. The viruses used were a genotype C2 virus isolated in The Netherlands in 1991 (MV-Bil) and a genotype B3 virus isolated from a severe measles case in Sudan in 1997 (MV-Sudan). Following infection, all rhesus monkeys developed a skin rash and conjunctivitis, which were less obvious in cynomolgus monkeys. Fever was either mild or absent in both species. Virus reisolation profiles from peripheral blood mononuclear cells and broncho-alveolar lavage cells and the kinetics of MV-specific IgM and IgG responses were largely identical in the two animal species. However, in animals infected with MV-Sudan, viraemia appeared earlier and lasted longer than in animals infected with MV-Bil. This was also reflected by the earlier appearance of MV-specific serum IgM antibodies after infection with MV-Sudan. Collectively, these data show that cynomolgus and rhesus macaques are equally susceptible to wild-type MV infection, although infection in the skin seems to follow a different course in rhesus macaques. MV-Sudan proved more pathogenic for non-human primates than MV-Bil, which may render it more suitable for use in future pathogenesis studies.

Measles vaccination of macaques by dry powder inhalation

Measles vaccination via the aerosol route has proven effective under field conditions, using vaccine reconstituted prior to nebulization. Inhalation of a dry powder aerosol vaccine would have additional benefits, including easier logistics of administration, reduced cold chain dependence and the potential of single dose administration. We have evaluated two candidate dry powder measles vaccine formulations in macaques. Specific immune responses were demonstrated, but levels of immunity were lower than in animals vaccinated by injection or by nebulized aerosol. These studies provide proof of principle that dry powder inhalation is a possible route for measles vaccination, but suggest that either the vaccine formulation or the method of delivery need to be improved for a better immune response.