By Donald G. McNeil Jr.
July 23, 2018
The New York Times reported on a Lancet paper which details a case whereby an asymptotic mother and baby survived where the rest of the family were infected and killed.
From the summary of the Lancet paper:
"Based on serology and epidemiological and genomic data, the most plausible scenario is that a female case in the November, 2015, cluster survived Ebola virus disease in 2014, had viral persistence or recurrent disease, and transmitted the virus to three family members a year later."
Note that this is a guess and not the only possible explanation, this is an explanation from industry, who do not have a working vaccine.
"On Nov 17, 2015, a 15-year-old boy presented to a
hospital in Monrovia, Liberia, with symptoms consistent
with Ebola virus infection. A blood specimen obtained
from the patient tested positive on Nov 19, 2015, for the
presence of Ebola virus RNA and health authorities were
notified immediately of the confirmed diagnosis of Ebola
virus disease"
"A non-research determination was issued by the CDC and the US Army
Medical Research Institute of Infectious Diseases Office
of Human Use and Ethics for this public health outbreak
investigation".
"Both the 15-year-old boy
(individual A) and his 8-year-old brother (individual C)
received ZMapp (Mapp Biopharmaceutical, San Diego,
CA, USA) as part of the Partnership for Research
on Ebola Virus in Liberia (PREVAIL) medical countermeasures
study by the Liberia Ministry of Health and
US National Institutes of Health. Individual A died
on Nov 23, 2015."