A small group of health care workers at intermediate or high risk of developing Ebola virus disease after exposure to the virus did not develop the disease after being treated with postexposure prophylaxis, according to Dr. Michael Jacobs and his associates.

Of eight health care workers evacuated to the United Kingdom between January and March 2015 and assessed using an Ebola risk calculator, four were deemed to be at intermediate or high risk for developing Ebola virus disease (EVD) and were started on postexposure prophylaxis (PEP) using oral favipiravir over 10 days. In addition, two of the four also were treated with monoclonal antibodies to Ebola glycoproteins. The favipiravir, administered in high dosages, was tolerated well by the four patients, the investigators reported in Lancet Infectious Diseases.

The second half of the eight-person study group had a low risk of EVD after assessment, and patients in this group were watched carefully, receiving no other form of treatment. No EVD developed in this low-risk group.

It cannot be known “whether or not PEP prevented the onset of Ebola virus disease in any of these individuals. However, two individuals had very high risk of Ebola virus transmission, and these are the first reported cases of transcutaneous, hollow-bore needlestick injuries contaminated with fresh blood that have not resulted in Ebola virus transmission,” noted Dr. Jacobs of the department of infection at Royal Free London NHS Foundation Trust and his associates.

In a related comment, Dr. Mark J. Mulligan and Dr. Paul N. Siebert said, “A needed next step is the development of a consensus risk determination algorithm devised by an expert panel, drawing on all available evidence, endorsed by health organizations, and disseminated to the field. The algorithm could be accompanied by a chart abstraction and case report form to standardize and organize data gathering.”

Dr. Mulligan and Dr. Siebert of the division of infectious diseases at Emory University in Atlanta added, “These data for recognized exposures in health care workers could be collated and analyzed in an international registry.”

Find the full study here: Lancet Infect Dis. 2015 Aug 26. doi: 10.1016/S1473-3099(15)00228-5.