The Ebola outbreak disrupted a planned measles vaccination campaign.
The Ebola crisis in West Africa is one of the most notable public health emergencies in recent years. The fast-spreading virus has killed more than 9,951 people since the outbreak began in December 2013, according to the Centers for Disease Control. Currently, there are no FDA-approved vaccines or antiviral treatments for Ebola, and patients’ survival depends on their own immune response and the supportive care they receive. The mortality rate for this disease is currently estimated to be about 70 percent by the World Health Organization.
Now a new study published in the journal Science suggests that the Ebola crisis could leave countries vulnerable to epidemics of a common virus, measles, due to the disruption of routine health care in affected areas.
The authors of this study are affiliated with some of the world’s leading public health institutions, including Princeton University, Johns Hopkins’ Bloomberg School of Public Health and the National Institutes of Health. They predict that due to the loss of health workers due to the Ebola crisis, a cluster of children not vaccinated against measles will accumulate in Guinea, Liberia and Sierra Leone. Because of the susceptibility of this population, the researchers expect a regional measles outbreak of 127,000 to 227,000 cases after 18 months, resulting in 2,000 to 16,000 measles-related deaths in the region.
Thanks to the efforts of the World Health Organization’s Comprehensive Immunization Program and additional immunization campaigns, childhood deaths from preventable diseases fell by more than 50 percent between 2000 and 2010 — a success story you don’t hear enough about. Measles vaccination has been an important aspect of this public health victory, as annual estimated measles deaths worldwide have fallen from 499,000 to 102,000 since 2004. Ebola-affected countries have benefited enormously from this reduction in measles deaths, but their susceptibility to measles has grown in recent years. Prior to the Ebola outbreak, there was a planned measles vaccination campaign in this area.
Historically, it is not uncommon for a measles epidemic to follow a humanitarian crisis. Measles is a highly transmissible infection and vaccination coverage is often low. Once measles is introduced into a population, it can spread very quickly. This was recently seen in the measles outbreak in the US, which was likely caused by a single infected traveler visiting a Disney theme park in California. Due to the collapse of healthcare systems during a crisis, a post-crisis population is particularly vulnerable to measles. And historically, measles outbreaks have occurred after wars, natural disasters, and political crises.
To investigate the relationship between Ebola-related healthcare disruptions and an increased risk of measles, the researchers of this study examined the geographic distribution of unvaccinated children and the measles susceptibility profile for affected countries before and after the Ebola crisis. Data from the demographic and health surveys in Guinea, Liberia, Sierra Leone and surrounding countries were used to estimate vaccination coverage in the region. Researchers used a Bayesian analysis model, which allows statisticians to estimate the likelihood of future events based on knowledge of past events.
The researchers estimate the number of unvaccinated children at six months, 12 months and 18 months after a 75 percent reduction in routine vaccination. Here, the authors modeled three scenarios based on three possible durations of disruption to usual healthcare as a result of the Ebola crisis: the crisis has not yet been resolved, so the duration of the possible disruption is not yet known. Their assumption of a 75 percent reduction in vaccination coverage is based on some surveys of healthcare providers in the Ebola-affected region, though they note that no reliable information is available on the change in vaccination coverage.
The authors estimated the full susceptibility of the population nationally after eight months of disruption by combining estimates of unvaccinated children with immunization histories and previous natural infection rates. They also calculated the expected size of a regional measles outbreak using the previously observed relationship between the population’s susceptibility to measles and the percentage of susceptible people who became infected in previous measles outbreaks. Finally, they were able to estimate the expected number of deaths from measles after the Ebola crisis by using known information about measles fatalities among infected individuals.
With these calculations, the researchers were able to estimate that for every additional month of healthcare disruption due to the Ebola outbreak, the number of children not vaccinated against measles increases by an average of 19,514. After six months of healthcare disruption, they estimate that 964,346 children will not be vaccinated against measles. After 12 months that number rises to 1,068,833 children and after 18 months an estimated 1,129,376 children in this region will not receive the vaccination.
Had measles vaccination continued at pre-Ebola rates during the Ebola outbreak, a general measles outbreak would have caused an estimated 126,868 cases. However, with an 18-month interruption of routine health care due to the Ebola crisis, a post-Ebola measles outbreak would lead to nearly double the number of cases (an estimated 227,484 cases) and an estimated increase of 5,209 deaths from measles.
Measles is just one of many childhood infections where vaccination rates have fallen due to the Ebola outbreak in West Africa; setbacks in vaccination programs could increase the incidence of polio and tuberculosis in this region. Disruption to other public health services can also increase the effects of malaria and HIV.
The authors note that chronic diseases such as HIV and non-age related infections such as malaria require constant intervention and support, while the effects of childhood infections such as measles can be combated with a single planned vaccination campaign. The authors recommend an increased vaccination campaign in West Africa to avoid a second post-Ebola public health disaster. Planning for this campaign must begin immediately as the pool of susceptible children is growing daily and a second public health crisis would seriously affect the population of an already devastated region.
Science2015. DOI: 10.1126/science.aaa3438 (About DOIs).