Ebola prediction dismissed
THE forecast that Ebola may infect 1.4-million people in Sierra Leone and Liberia by January looks too far into the future to be a meaningful prediction, health officials say.
THE US Centers for Disease Control and Prevention’s (CDC’s) forecast that Ebola may infect 1.4million people in Sierra Leone and Liberia by January looks too far into the future to be a meaningful prediction, health officials say.
The virus that has infected 5,843 people may cause 550,000 to 1.4-million infections in those countries by January 20 if no action is taken to curb the epidemic in West Africa, the CDC said in a report on Tuesday.
Earlier, researchers from the World Health Organisation (WHO) and Imperial College London predicted the epidemic may exceed 20,000 cases by November 2, according to a study published in the New England Journal of Medicine.
Predicting the course of the epidemic helps health agencies, including the CDC and WHO, to determine the resources needed to control it.
However, the unprecedented nature of the outbreak and the fact that the global response is now gathering pace make projecting more than a few weeks into the future impossible, said London School of Hygiene and Tropical Medicine director Peter Piot, a codiscoverer of the Ebola virus.
“Unless the CDC has data nobody else has, this is not a useful estimate,” Prof Piot said on Tuesday. “We should certainly not assume that our collective efforts won’t have any impact.”
The CDC model predicts about 21,000 cases by the end of this month, assuming that for every diagnosed case, 1.5 go unreported. The WHO model predicts a similar number if extended to January, but the Geneva-based
Unless the CDC has data nobody else has, this is not a useful estimate
agency’s researchers were not confident enough to make forecasts that far into the future, said WHO director of strategy Chris Dye, a co-author of the paper.
“This epidemic is like weather forecasting,” Prof Dye said. “We can go a week, maybe two weeks into the future, but beyond that everything is uncertain.
“We’ve made the best judgment we can, and in our judgment it’s not valid to go any further than four weeks ahead.”
The challenge for outbreak forecasters is to find a balance between raising an alarm and “going over the top”, he said.
Sierra Leone does not expect to have as many cases as the CDC’s model predicts, the country’s Emergency Operations Centre spokesman Sidie Yahya Tunis said. “That is why we are putting extraordinary measures in place to make sure we break the chain of transmission,” Mr Tunis said.
By projecting the outbreak to January, the CDC was able to confirm a tipping point at which the epidemic could be sharply reversed, spokeswoman Barbara Reynolds said yesterday.
The CDC’s model, which excludes Guinea, also allows other researchers to plug in data to predict the impact of different interventions over the coming months, according to director Tom Frieden.
“Part of the point of having a projection of what might happen if we don’t take urgent action is to make sure it doesn’t happen,” Dr Frieden told reporters on Tuesday. “That’s what we hope and anticipate this will result in,” he added.