Just as the terrible tide of Ebola is seeming to finally draw back from Liberia and the geographical distribution of cases in Africa is contracting, a new wave of disease may be poised to rush in to hard-hit West Africa: measles. New research published in the journal Science suggests that the strain Ebola has placed on local infrastructures leaves populations vulnerable to the next opportunistic pathogen.
“Even after the last Ebola case recovers, the disruptions of local health systems caused by the outbreak could lead to a second infectious disease crisis that could kill as many as, if not more than, the original outbreak,” Princeton University researcher Saki Takahashi and colleagues wrote in their paper.
During the past year, many health centers in Liberia, Guinea, and Sierra Leone—the three countries most impacted by Ebola—had to close. Others stayed open, but fear of catching Ebola meant that many people stopped coming in for other services, including getting their children vaccinated for diseases like measles.
“Measles in particular is known to show up during or after humanitarian crises because it’s so infectious,” coauthor and Johns Hopkins scientist Justin Lessler said in a conference call with reporters.
Using data from health surveys combined with demographic rates, Takahashi, Lessler, and their team set out to map the probability that children had received measles vaccines in the Ebola-hit region during and in the immediate wake of the crisis. Estimating a 75 percent drop in measles vaccination rates due to Ebola disruptions, the team calculated that the three countries would see an estimated ~350,000 additional unvaccinated children in about 18 months. Based on previous measles outbreaks in the region, the team estimated that this would translate into 100,000 additional cases of measles, of which between 2,000 and 16,000 would be fatal. And as with Ebola, the measles cannot be expected to stay within national borders.
“The growing pool of susceptible individuals in Guinea, Liberia, and Sierra Leone may place bordering countries at increased risk for a measles outbreak; they too may have suffered disruptions to their health care systems due to a focus on the threat from Ebola,” Takahashi and colleagues wrote. “These countries should carefully assess the performance of their vaccination programs and consider instituting campaigns to shore up any gaps.”
According to Shobana Shankar, a historian at Stony Brook University who studies the social and cultural politics of medicine (and who is unaffiliated with the current paper), historical evidence affirms that measles outbreaks can crop up in West Africa after major catastrophes and epidemics. Also, she says, climate variability is another factor that has to be considered in these secondary waves of disease.
“Although colonial-era statistics (c.1900-1960) for measles are not complete, evidence shows that, in the dry season between December and February and extreme heat of the Harmattan”—a hot, dry trade wind that blows over West Africa—“between March and April, spikes in temperature have aggravated measles and meningitis outbreaks,” Shankar wrote in an email. “The first recorded outbreaks of Lassa fever, a virus causing symptoms similar to those of Ebola, occurred in Liberia, Nigeria, and Sierra Leone mostly in the first part of the dry season, with measles and meningitis following in the hotter months before the rainy season.”
The post-Ebola measles threat is still largely one on paper; currently, there are some reports of measles cases in the region covered by the study, but health officials have not seen any major outbreaks just yet. The authors acknowledge that their findings may be a touch pessimistic, and if vaccination campaigns can get up and running soon, this dark scenario could be averted. Prior to this Ebola outbreak, measles had been substantially beaten back in the three countries thanks to vaccines. Just around 7,000 measles cases were reported to the World Health Organization in Liberia, Guinea, and Sierra Leone between 2004 to 2013—compare that to the more than 93,000 cases reported between 1994 and 2003.
“My hope is that at least partial vaccination campaigns occur and that routine vaccination wraps up much better than we expect, so that we never have to find out if our projections were correct,” Lessler said.