Current vaccination strategies are unlikely to eliminate measles, according to a new study led by professors at the University of Georgia.
The paper, which was published today in The Lancet Global Health , explores the feasibility of eliminating measles and rubella using the prevailing vaccination strategies in 93 countries with the highest disease burden.
Despite marked reductions in the number of new measles and rubella cases worldwide, gaps remain between current levels of transmission and elimination of the disease.
“Measles is one of the most contagious respiratory infections out there, and it spreads quickly, making it difficult to control,” said lead author Amy Winter, assistant professor of epidemiology and biostatistics at the UGA School of Public Health.
The basic reproduction number (R0) for measles, which represents the number of people to whom an infected person is likely to transmit that disease in a fully susceptible population, is about 18. By comparison, the R0 for the SARS-CoV-2 virus Original CoV-2 is estimated to be around three.
In 2017, the director general of the World Health Organization requested a report on the feasibility of measles and rubella eradication. One component of this report was to use transmission models to evaluate the theoretical feasibility of eradicating the two viruses given different vaccination strategies.
The evaluation was a collaboration with the WHO Measles and Rubella Expert Strategic Advisory Working Group, the World Health Organization, the US Centers for Disease Control and Prevention, and five modeling groups. .
Using four national disease transmission models and one subnational model, the modeling groups projected annual measles and rubella case rates for two vaccination scenarios.
Both vaccination scenarios use the two predominant vaccination approaches of routine vaccination as part of childhood vaccination schedules and national vaccination campaigns.
The first “business as usual” vaccination scenario continues vaccination coverage and campaigns in the future. The second “stepped up investment” vaccination scenario optimally improved vaccination coverage over time. This scenario also included vaccination campaign cessation criteria: a stopping point for when campaigns are no longer considered necessary because a sufficiently large proportion of the population has been inoculated.
The models show that current vaccination strategies could eliminate rubella and congenital rubella syndrome in all 93 counties, but not measles.
“The current strategy that we use, which focuses on improving routine vaccination coverage and complementing it with nationwide vaccination campaigns until routine vaccination is high enough, that alone will not be enough to achieve elimination of the measles. We need novel approaches,” Winter said.
The authors evaluated two strategies that could help a country move toward elimination faster and reduce the likelihood of measles outbreaks: one, improving the way supplemental vaccine campaigns are carried out to ensure they reach children who do not receive routine vaccinations.
Two, improve equity in vaccination coverage by targeting routine and supplemental vaccination in the subregions with the lowest vaccination coverage first so that they are at the same level.
“A world permanently free of measles and rubella would be an incredible achievement for humanity. Our work suggests that to achieve this goal, we need to make vaccine coverage much more equitable,” said co-author Mark Jit, professor of vaccine epidemiology at the London School of Hygiene and Tropical Medicine.
“In other words, we must work even harder to bring measles and rubella vaccination to the most disadvantaged people in the world.”
The final strategy the authors present is a reconsideration of the cessation criteria. Currently, most countries stop supplementing routine vaccinations with vaccination campaigns once they reach elimination status, Winter said, but modeling suggests that outbreaks are still likely to occur if countries rely only on vaccinations. routine.
It is essential, Winter warns, to remain vigilant to monitor cases of rubella and measles and to respond quickly to potential outbreaks even after elimination is achieved.
“We have a globally connected world, so there is constant pressure of virus imports in places where it has already been eliminated,” he said. “That is why it is important to maintain high vaccination coverage and continue improving surveillance of these diseases.”
Findings The intensified investment scenario led to large reductions in the incidence and burden of measles and rubella. It is likely that rubella elimination can be achieved in all countries and measles elimination in some countries, but not all. The PSU and DynaMICE national measles models estimated that by 2050, the probability of elimination would exceed 75% in 14 (16%) and 36 (39%) of the 93 modeled countries, respectively. Subnational measles transmission modeling highlighted inequity in routine coverage as a likely driver of continued endemic measles transmission in a subset of countries. Interpretation To achieve regional elimination goals, it will be necessary to innovate vaccination strategies and technologies that increase the spatial equity of routine vaccination, in addition to investing in existing surveillance and outbreak response programs. |
