One of the Ebola vaccines about to enter testing in Liberia may not be as potent as researchers had hoped, according to a new study, raising questions about how well it will prevent infection.
The vaccine, developed by GlaxoSmithKline, is one of two in a large-scale clinical trial expected to begin in the next two weeks. Merck produced the other vaccine.
Earlier studies had found that one dose of the GSK vaccine would protect monkeys from Ebola.
However, in the study published in the New England Journal of Medicine, “What we see are immune responses that are several-fold lower than were seen in those monkey studies,” said study co-author Adrian Hill, director of the Jenner Institute at the University of Oxford.
“That raises the question, will it work as well in people as in monkeys? The short answer is we don’t know,” he added, “but that’s exactly the question the trials in Liberia and elsewhere are designed to address.”
The trial in Liberia will use a higher dose of the vaccine. A study of a related vaccine published in November found patients given a higher dose developed a stronger immune response. Monkeys with a comparable response were protected from infection.
The Merck vaccine has been undergoing early tests as well, but data from those studies have not been published.
Researchers are moving at record speed to develop a vaccine in response to the unprecedented Ebola outbreak centered in Liberia, Guinea and Sierra Leone. More than 22,000 people have been infected and nearly 9,000 have died.
The declining number of new infections is good news for health workers, but may make it more difficult to determine the effectiveness of a vaccine.