Ebola quarantine period is NOT long enough: Deadly virus could lay dormant in the body for longer than 21 days, expert claims


  • The World Health Organisation advises the incubation period for the Ebola virus is two to 21 days
  • After that point a person who shows no signs of the virus is deemed clear
  • But Professor Charles Hass, from Drexel University in Philadelphia said this time period 'must be reconsidered'
  • Studying past outbreaks he said there is a 12% chance the deadly virus could lay dormant in a person's body for longer than three weeks


By Lizzie Parry for MailOnline
Published: 12:09 EST, 16 October 2014 | Updated: 13:31 EST, 16 October 2014


The recommended 21-day quarantine period for the Ebola virus is not long enough to contain the spread of the disease, a new study has warned.

The World Health Organisation (WHO) advises the incubation period for the virus is between two and 21 days.

It is thought that if someone who has been in contact with an Ebola victim but does not develop symptoms after that point, has not been infected.

But a study by scientists at Drexel University in Philadelphia has found there is a 12 per cent chance the deadly virus could lay dormant in a person's body for longer than the three-week period.



A Nigerian health official uses a thermometer to check for Ebola on a worker at the arrivals hall of Murtala Muhammed International Airport in Lagos . However a study warned today there is a 12 per cent chance the deadly virus could lay dormant in a person's body for longer than the three-week incubation period



A medical worker sprays people being discharged from the Island Clinic Ebola treatment centre in Monrovia, Liberia. The findings of the new study mean a significant proportion of the population in West Africa could be developing the disease outside of the key incubation period

It means a significant proportion of the population in West Africa could be developing the disease outside of the key incubation period.

Biologist professor Charles Hass said when calculating the isolation period on the basis of past outbreaks, there is always a 'standard deviation for results' - a percentage by which they may vary - which has yet to be taken into account during this outbreak.

Professor Hass, who has vast experience of analysing the risk of transmitting biological pathogens, said 'reconsideration is in order' as 21 days may not be sufficient to protect public health.

He said: 'Twenty one days has been regarded as the appropriate quarantine period for holding individuals potentially exposed to Ebola Virus to reduce risk of contagion, but there does not appear to be a systemic discussion of the basis for this period.'

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Data gathered by the WHO from earlier outbreaks in Zaire and Uganda reported an incubation period of between two and 21 days for the virus, meaning if the individual has not presented with symptoms after three weeks they are unlikely to be infected or contagious.
Professor Haas said he believes a broader look at risk factors should be considered as with any research of this nature there is a standard deviation in results.
In the case of Ebola's incubation period the range of results generated from Zaire and Uganda varied little, and this may have contributed to the WHO's certainty.
CDC chief says Ebola in Africa could imperil US healthcare system






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Ebola has killed more than 4,500 people in West Africa and wreaked havoc on the region. Biologist Charles Hass says the recommended 21-day quarantine period for the Ebola virus 'must be reconsidered'


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Isabelle Nuttall, of the World Health Organization (WHO) director of global capacities, alert and response global capacities listens to a question during a press conference on the Ebola epidemic outbreak on October 16, 2014 at the United Nations offices in Geneva. Ebola's escalating spread constitutes the worst global health emergency in years, world leaders warned, vowing to dramatically step up the response to the virus that has already killed nearly 4,500 people. AFP PHOTO / FABRICE COFFRINIFABRICE COFFRINI/AFP/Getty Images

But looking more broadly at data from other Ebola outbreaks in Congo in 1995 and West Africa recently suggests there could be up to a 12 per cent chance that someone could be infected even after the 21-day quarantine.
Professor Haas, whose research is published in PLOS Currents, said: 'While the 21-day quarantine value, currently used, may have arisen from reasonable interpretation of early outbreak data, this work suggests reconsideration is in order and 21 days might not be sufficiently protective of public health.'
He said these quarantine periods must be determined by looking at the cost of enforcing the quarantine against the that of releasing exposed individuals.
Looking at the potential trade off between costs and benefits as the quarantine time is extended should guide public health officials in determining the appropriate action.
But, with more contagious and potentially deadly diseases the cost of making a mistake on the short side when determining a quarantine is extremely high.
Professor Haas, added: 'Clearly for pathogens that have a high degree of transmissibility and a high degree of severity, the quarantine time should be greater than for agents with lower transmissibility and severity.
'The purpose of this paper is not to estimate where the balancing point should be, but to suggest a method for determining the balancing point.'