I’m still running into hordes of people claiming the incubation period for Ebola can be up to 42 days. It doesn’t help that multiple Right Wing sites (like WND) are pushing this false info too.
The problem comes from not understanding what it is that WHO is talking about in the cited report. You have to grasp that the report is not about individual incubation periods at all, it is about observed incubation periods within communities. (in this case entire countries)
So while the first paragraph of the “confusing” section states very clearly:
The period of 42 days, with active case-finding in place, is twice the maximum incubation period for Ebola virus disease and is considered by WHO as sufficient to generate confidence in a declaration that an Ebola outbreak has ended.
The trouble in understanding comes from the paragraph which follows that one:
Recent studies conducted in West Africa have demonstrated that 95% of confirmed cases have an incubation period in the range of 1 to 21 days; 98% have an incubation period that falls within the 1 to 42 day interval. WHO is therefore confident that detection of no new cases, with active surveillance in place, throughout this 42-day period means that an Ebola outbreak is indeed over.
Now if you don’t understand that this report is strictly about the community incubation period it appears that WHO just contradicted itself. If you have spent any time on twitter or in online comment sections I’m sure you have seen something like:
“Wait, first they said 21 days was the max and now they are saying it is 42!”
This interpretation is wrong for the very simple reason that WHO is not talking about the individual incubation period at all. What they are talking about is the time from the last known contact with an infected patient in a community.
Once the last known patient dies or recovers, 95% of additional cases have appeared in 21 days or less while a further 3% of cases have appeared between 22 and 42 days. So is WHO saying that the individual incubation period may be longer than 21 days with this information? Not. At. All.
Remember that they are discussing an entire country with this statistic, so to paraphrase this report in its simplest terms:
When all known cases are cleared 95% of new infection cases will appear within 21 days of that last case being resolved.
Another 3% of cases will appear between 22 and 42 days after the last known case is resolved through contact with an unknown case.
Nowhere in this report does WHO ever say that the individual incubation period is longer than 21 days. In fact the one time it does address the incubation period for individuals it specifically states that it is 21 days or less.
Thank you for reading. :)