Ebola control: effect of asymptomatic infection and acquired immunity
Bellan, Steve E et al.
The Lancet , Volume 384 , Issue 9953 , 1499 - 1500
Published Online: 15 October 2014 Evidence suggests that many Ebola infections are asymptomatic,[SUP]1[/SUP][SUP],[/SUP] [SUP]2[/SUP] a factor overlooked by recent outbreak summaries and projections.[SUP]3[/SUP] Particularly, results from one post-Ebola outbreak serosurvey[SUP]1[/SUP] showed that 71% of seropositive individuals did not have the disease; another study[SUP]2[/SUP] reported that 46% of asymptomatic close contacts of patients with Ebola were seropositive. Although asymptomatic infections are unlikely to be infectious,[SUP]2[/SUP] they might confer protective immunity and thus have important epidemiological consequences.
Although a forceful response is needed, forecasts that ignore naturally acquired immunity from asymptomatic infections overestimate incidence late in epidemics. We illustrate this point by comparing the projections of two simple models based on the Ebola epidemic in Liberia, a model that does not account for asymptomatic infections, and another that assumes 50% of infections are asymptomatic and induce protective immunity. In both models, the basic reproduction number (R[SUB]0[/SUB]) is identical and based on published estimates.[SUP]3[/SUP] The
figure shows the projected cumulative incidence through time. Although the initial outbreaks are almost identical, by Jan 10, the model without asymptomatic infections projects 50% more cumulative symptomatic cases than the model that accounts for asymptomatic infection. This difference arises because
asymptomatic infection contributes to herd immunity and thereby dampens epidemic spread...
