# 7449
The epidemiological yardstick by which human transmission of an infectious disease is measured is called the R0 (pronounced R-nought) or Basic Reproductive Number.
Essentially, the number of new cases in a susceptible population likely to arise from a single infection.
With an R0 below 1.0, a virus (as an outbreak) begins to sputter and dies out.
Above 1.0, and an outbreak can have `legs’.
Calculating the R0 is notoriously difficult, particularly since much hinges upon the existence and subtle differences between viral strains, the accuracy of surveillance and reporting, `seasonality’, and individual host responses to the virus (i.e. number of `super spreaders’).
Like the CFR (Case Fatality Ratio), the R0 can vary considereably over time or geography, often ends up being described as a `range’, and usually isn’t well established (or at least, generally agreed upon) until long after an outbreak has ended.
Today The Lancet publishes an analysis – based on very early surveillance numbers - that attempts to quantify the R0 of MERS-CoV, and its `pandemic potential’.
First a link to the abstract (and an excerpt), then a link to informative report by Helen Branswell that explains why we shouldn’t be lulled by these preliminary findings.
Interhuman transmissibility of Middle East respiratory syndrome coronavirus: estimation of pandemic risk
Romulus Breban PhD, Julien Riou, Prof Arnaud Fontanet PhD
Results
With our most pessimistic scenario (scenario 2), we estimated MERS-CoV R0 to be 0·69 (95% CI 0·50—0·92); by contrast, the R0 for prepandemic SARS-CoV was 0·80 (0·54—1·13). Our optimistic scenario (scenario 1) yielded a MERS-CoV R0 of 0·60 (0·42—0·80). Because of recent implementation of effective contact tracing and isolation procedures, further MERS-CoV transmission data might no longer describe an entire cluster, but only secondary infections directly caused by the index patient. Hence, we calculated that, under scenario 2, eight or more secondary infections caused by the next index patient would translate into a 5% or higher chance that the revised MERS-CoV R0 would exceed 1—ie, that MERS-CoV might have pandemic potential.
Interpretation
Our analysis suggests that MERS-CoV does not yet have pandemic potential. We recommend enhanced surveillance, active contact tracing, and vigorous searches for the MERS-CoV animal hosts and transmission routes to human beings.
Based on an extremely limited data-set, and hobbled by limited surveillance and reporting out of Saudi Arabia, the authors have produced an early estimate of the virus’ apparent R0 (which they fix at between .60 and .69).
Too low (at this time) to spark a pandemic.
But in the following Canadian Press article, Helen Branswell quotes a number of experts - including Drs. Allison McGeer, Marc Lipsitch, and Chris Bauch (who co-authored a commentary on this study) - who warn that past performance is no guarantee how this virus will behave in the future.
Follow the link below to read:
MERS doesn't have pandemic potential – yet
By Helen Branswell The Canadian Press
TORONTO – The new MERS coronavirus currently doesn’t spread well enough among people to trigger a pandemic, says a new study that calculates the rate at which the virus is transmitting person to person.
But the senior author says the pattern of how the virus is spreading now cannot be used to predict whether MERS will become a bigger threat in the future.
“There is absolutely no guarantee that this virus will stay as it is. It could very well follow the same path as SARS did 10 years ago,” Dr. Arnaud Fontanet, who heads the emerging diseases epidemiology unit at the Institut Pasteur in Paris, said in an interview.
Highly recommended.
