The W.H.O. said both outbreaks pose regional risks: Equatorial Guinea has porous borders with Cameroon and Gabon, and so far the cases have appeared in geographically diffuse parts of the country. In Tanzania, the Kagera region has busy borders with Uganda, Rwanda and Burundi.
These outbreaks follow one in Ghana last year and in Guinea the year before — a marked shift from the sporadic occurrences in previous years. Dr. Amuasi said better tracking was likely contributing to what appeared to be a rise in cases. As part of the response to the Covid-19 pandemic, he said, every African country improved its PCR testing capacity and infectious disease surveillance, which means Marburg is being diagnosed more frequently.
But that suggests there may have historically been more of the virus circulating among humans than has been thought, Dr. Amuasi said, and the way it sickens people may be different than has been understood.
Dr. Nancy Sullivan, the director of the National Emerging Infectious Diseases Laboratories at Boston University, said she believes climate change, and the way it is shifting human and animal behavior, is driving an actual increase in cases. “We’re impinging much more on reservoirs” of the virus, she said.
Dr. Sullivan designed the Marburg vaccine candidate farthest along in development when she worked with the National Institute of Allergy and Infectious Diseases. It showed safety and immune response in a Phase 1 clinical trial, and the Sabin Vaccine Institute, a nonprofit organization based in Washington that promotes global vaccine development, is continuing the testing process.
The Sabin Institute said it had 600 doses of the vaccines in vials and ready to use and planned for an eventual stockpile of 8,000 by the end of this year. Dr. Sullivan said 600 doses would be enough to start a ring vaccination trial of those at risk in Tanzania and Equatorial Guinea.
But the W.H.O. has yet to announce operational details for a trial of this or three other vaccine candidates. Transporting the doses into the country is just one challenge; a trial would require a principal investigator from the outbreak country, legal agreements with the vaccine makers and regulatory approval. Equatorial Guinea has a notoriously opaque government that has been under the control of President Teodoro Obiang Nguema Mbasogo and his family for more than 30 years.
Without committed resources and preapproved trial protocols, filovirus outbreaks will keep happening with little progress on interventions that could stop them, Dr. Amuasi said.
