An international consortium of researchers has reported that an Ebola vaccine appears to provide volunteers protection against the virus two years after they were injected — encouraging findings both for the public health community and the vaccine’s manufacturer.

An earlier study, conducted in Guinea near the end of the devastating West African Ebola outbreak, showed the vaccine from Merck, which is given in a single shot, rapidly generated protection against the virus. But how long that protection lasts remained an open question.