In a recent study published in The Lancet Global Health, researchers modeled the probability of eradication of measles and rubella by 2100.
The global increase in vaccination coverage for measles and rubella has substantially reduced infections and disease burden. Measles has been eradicated from 81 countries and rubella from 93 countries as of January 2021. Global measles cases have resurged in all regions from 2017, with a 556% increase between 2016 and 2019.
The target to achieve rubella and measles elimination by 2020 has not been met in five World Health Organization (WHO) regions. Moreover, many countries have been left susceptible to outbreaks due to the lower vaccination coverage in 2020 and disruptions ensued by the coronavirus disease 2019 (COVID-19) pandemic.
The WHO Director-General was requested at the Seventieth World Health Assembly in 2017 to report in three years on the feasibility and epidemiologic aspects of and resource requirements for eradicating measles and rubella. Accordingly, a feasibility assessment for eradicating rubella and measles was conducted. One of its objectives was to model vaccination scenarios to examine the feasibility of measles and rubella eradication.
About the study
In the present study, researchers modeled the probability of eliminating measles and rubella from 93 countries of interest. Vaccination strategies relied on historical data of vaccination coverage for routine immunization and supplemental immunization activities (SIA). Two vaccination scenarios were developed: 1) business-as-usual approach in which current vaccination coverage was continued, and 2) intensified investment approach that (optimally) increased vaccination coverage into the future.
These vaccination scenarios were evaluated in the context of one sub-national and two national models for rubella transmission and two national models for measles transmission. The four national models were the 1) Johns Hopkins University (JHU), 2) Public Health England (PHE), 3) dynamic measles immunization calculation engine (DynaMICE), and 4) Pennsylvania State University (PSU) models.
Ninety-three low-, lower-middle, and upper-middle-income nations with the highest burden of measles and rubella were selected for analysis. The sub-national model based on the Institute of Disease Modeling simulated measles dynamics in Nigeria. Two-hundred stochastic simulations were run per country for each model from 1980 to 2100.
The models estimated distributions of the annual number of expected measles or rubella cases per country, which were analyzed to assess the impact of each vaccination strategy on health outcomes and the probability of eradicating measles and rubella. Elimination was defined as five or fewer annual infections occurring per million people.
The burden of rubella was projected to remain high from 2020 to 2100 in the business-as-usual scenario. Many countries were projected to eliminate rubella by 2020, as most had introduced rubella vaccines by 2017. All countries projected for rubella eradication by 2020 reported five or fewer rubella cases per million individuals from 2017 to 2020. Nonetheless, 23 countries did not introduce vaccines, which would drive rubella infections, congenital rubella syndrome, and associated deaths.
In the intensified investment approach, the incidence of rubella and congenital rubella syndrome was projected to decline substantially from 2020 to 2100. The probability of eradicating rubella was higher and possible in a shorter period than in the business-as-usual approach. The PHE and JHU intensified investment models revealed that elimination was generally sustained once the criteria for rubella eradication were met.
The DynaMICE and PSU models under the business-as-usual approach projected 16 and 19 countries to achieve measles elimination by 2020. Most countries from either model reported five or fewer measles cases per million individuals during 2017-20. The DynaMICE model projected a median of 20 million measles infections and 469,000 deaths annually during 2020-2100 for the remaining countries, while the PSU model projected 17 measles cases and 441,000 deaths annually.
The intensified investment approach predicted a marked decline in measles cases and mortality. The DynaMICE model projected a median of 900,000 measles infections and 3,000 deaths annually from 2020 to 2100. The PSU model projected a median of 2.1 million measles infections and 28,000 deaths annually for the same period. More countries under this vaccination were projected to achieve measles eradication and, in less time, than in the business-as-usual scenario.
Although it was possible in the intensified investment scenario for all countries to eradicate measles, the probability was low. The sub-national model of Nigeria revealed qualitatively comparable projections. Notably, this model underscored that inequity in routine vaccination coverage could drive the continued transmission of endemic measles in a subset of nations.
In summary, the authors found that increased vaccination coverage in the intensified investment approach would probably create necessary conditions to eradicate rubella in all countries. However, eliminating measles would be unlikely in some countries even when necessary conditions are met. This is because elimination often cannot be maintained without a continued vaccination program. Altogether, the findings suggest that with sustained coverage of measles and rubella vaccination, it is possible to achieve and sustain measles and rubella eradication.