London School of Hygiene & Tropical Medicine

More investment and innovation in vaccination strategies could lead to the elimination of rubella in 93 countries, and measles in up to 36 countries, according to a new study led by the University of Georgia (UGA) and the London School of Hygiene & Tropical Medicine (LSHTM). 

The paper, which was published in The Lancet Global Health, explores the feasibility of eliminating measles and rubella between 2020 and 2100 by focusing on two different  vaccination scenarios in 93 countries with the highest measles and rubella burden.

The assessment was a collaboration between a large host of partners, which also included The Bill & Melinda Gates Foundation, the University of Southampton, the Johns Hopkins School of Public Health, Ramboll Health Sciences, the World Health Organization (WHO) Strategic Advisory Group of Experts Measles and Rubella Working Group, the World Health Organization, and the US Centers for Disease Control and Prevention (CDC).

Overall, there has been a marked reduction in cases of measles and rubella since the widespread use of vaccines. However, between 2017 and 2019 there has been a 556% rise in cases of measles, with large outbreaks of the disease in Ukraine, Madagascar and the Democratic Republic of Congo. The COVID-19 pandemic and the spread of misinformation about vaccines has also left many countries susceptible to future outbreaks.

Although no global goal for measles eradication has been established, all six WHO regions have set measles elimination targets. However, a gap remains between current control levels and elimination targets, as shown by recent large measles outbreaks.

The study’s lead author Amy Winter, an Assistant Professor of Epidemiology and Biostatistics at UGA’s College of Public Health, said: “Measles is one of the most contagious respiratory infections out there, and it moves quickly, so it is hard to control.”

In a susceptible population, each person infected with measles is likely to transmit the disease to roughly 18 people. By comparison, this number for the original SARS-CoV-2 virus is estimated to be around 3.

This study aimed to model the potential for measles and rubella elimination globally to inform a WHO report to the 73rd World Health Assembly on the feasibility of measles and rubella eradication.

Using four national disease transmission models and one sub-national model, the modelling groups projected the annual case rates for measles and rubella for two vaccination scenarios.

Both vaccination scenarios use the two predominant vaccination approaches of routine vaccination as part of childhood immunisation schedules and nationwide vaccination campaigns.

The vaccination scenarios included a so-called “business as usual” approach, which continues present vaccination coverage, and an “intensified investment” approach, which increases coverage into the future.

The annual numbers of infections projected by each model, country, and vaccination scenario were used to explore if, when, and for how long the infections would be below a threshold for elimination.

In the business as usual scenario, the burden of rubella was projected to remain high, but as most countries had introduced rubella-containing vaccines by 2017 many were projected to achieve elimination by 2020. In the intensified investment scenario, the number of cases was projected to drop significantly, and elimination was projected as a possibility in all 93 countries included in the study.

For measles, the two models suggested that the business as usual scenario could result in the right conditions for elimination in 16 and 19 of the 93 countries included. The intensified scenario predicted a marked reduction in the burden of measles cases and mortality, with more countries projected to achieve elimination and in a shorter time. In this scenario, the two models estimated that, by 2050, the probability of elimination would exceed 75% in 14 and 36 of 93 modelled countries, respectively.

The authors found that better vaccine coverage in the intensified investment scenario is likely to result in the necessary conditions for rubella elimination in all countries, and in large reductions in measles incidence and mortality, despite increases in population size. However, measles elimination will remain unlikely in a subset of countries because, even if the necessary conditions for elimination are achieved, elimination often cannot be maintained without continued vaccination campaigns.

Dr Winter said: “The current strategy that we use, which is focused on improving routine vaccination coverage and supplementing it with nationwide vaccination campaigns until routine vaccination is high enough, but that alone is not going to be sufficient to reach measles elimination. We need novel approaches.” 

Mark Jit, Professor of Vaccine Epidemiology at LSHTM and senior author of the paper, said: “A world that is permanently free of measles and rubella would be an incredible achievement for humanity. Our work suggests that to reach this goal, we need to make vaccine coverage much more equal. In other words, we need to work even harder to bring measles and rubella vaccination to the most underserved people around the world.”

The authors evaluate two strategies that could help move a country to elimination faster and reduce the probability of measles outbreaks: one, improve how supplemental vaccine campaigns are delivered to make sure they are reaching children who are not receiving routine vaccinations. Two, improve vaccine coverage equity by focusing routine and supplemental vaccination on sub-regions with the lowest vaccination coverage first to get them up to par.

Dr Winter said: “And the final strategy we discuss is that we should reconsider our criteria under which vaccinations stop happening, meaning we should allow the potential for vaccination campaigns to continue to some degree after a country reaches elimination.”

Currently, most countries stop supplementing routine vaccines with campaigns once they reach measles elimination status but the models suggest that outbreaks are still likely to occur if routine vaccines alone are relied upon.

Dr Winter said: “We have a globally connected world, so there is this constant pressure of importations of the viruses in places where it is already eliminated, that is why keeping vaccination coverage high and continuing to improve surveillance for these diseases is important.”

The study points to several limitations. For example, the models were not able to account for cross-border transmission, which could have resulted in an over- or under-estimation regarding elimination and numbers of vaccinated children were likely to have been over-estimated.

Publication

Amy Winter et al., Feasibility of measles and rubella vaccination programmes for disease elimination: a modelling study. Lancet Global Health. DOI: 10.1016/S2214-109X(22)00335-7