The global emergency stockpile of Ebola vaccines will grow to 500,000 doses following a decision Thursday by the board of Gavi, the Vaccine Alliance. Previously the target for the stockpile had been 300,000 doses.

The Gavi board also agreed to support a program of targeted preventive vaccination of key front-line health workers in Ebola at-risk countries, though details of how many and how soon remain to be worked out.

“We think it’s important to have a comprehensive view of Ebola going forward, given the devastation that it can do in countries at risk,” Gavi CEO Seth Berkley said during a teleconference from New Delhi, where the organization’s board met.

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The decision to increase the size of the stockpile reflects the fact that while 300,000 doses seemed more than adequate when Gavi first announced it after the West African Ebola outbreak of 2014-2016, the experience with the current outbreak in the Democratic Republic of the Congo has led most experts to conclude it would not be sufficient.

More than 255,000 doses of Ebola vaccine have been used to date in this outbreak in the DRC and there have been fears at times that supplies would run out.

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The new size of the stockpile was set based on advice from the World Health Organization’s Strategic Advisory Group of Experts on Immunization, known as SAGE. Berkley said decisions on the pre-vaccination program would also be made based on recommendations from SAGE.

In the event of an Ebola outbreak, vaccine in the stockpile would be made available for free to low- and middle-income countries, to date the only ones where indigenous Ebola outbreaks have occurred. Those countries will also receive financial help to cover the costs of administering the vaccine.

Should outbreaks occur in upper income countries, they will also be able to draw on the stockpile. But they will have to pay for the vaccine, Berkley said.

That type of need could conceivably arise if a traveler or a health worker who volunteered in an outbreak became infected and returned home sick, igniting some transmission in a country where Ebola typically is not found.

Such a case occurred in United States in 2014, during the West African Ebola outbreak, when a Liberian man who had been living in Dallas was infected during a visit to his homeland. Two nurses who cared for him in Dallas were infected.

The United States is expected to purchase Ebola vaccine for inclusion in the strategic national stockpile; some other high-income countries may follow suite. Several dozen countries have sent response workers to Ebola outbreaks over the years; some of those may opt not to procure their own stockpiles and instead plan to draw on Gavi supplies if they need a few doses on rare occasions.

Currently there are eight candidate Ebola vaccines, all targeting Zaire ebolaviruses, the species that has caused the most outbreaks since Ebola was first discovered in 1976. Ebola Zaire is the virus responsible for the current long-running outbreak in the DRC.

Any of these vaccines could end up in the stockpile, Berkley said. But only vaccines that have been licensed and have been pre-qualified by the WHO would be considered for purchase. WHO pre-qualification is a vetting system — similar to those used by the Food and Drug Administration or other national regulatory agencies — to determine that medical products are effective and safe.

At the moment only Merck’s vaccine, Ervebo, meets both criteria. But China and Russia have licensed Ebola vaccines. Those products could be considered for the stockpile if they receive WHO pre-qualification.

Johnson & Johnson has an Ebola vaccine — now being used in a trial in DCR — that is likely to be licensed within the timeframe during which the Gavi stockpile will be amassed. But Berkley noted that the J&J vaccine — given in 2 doses 56 days apart — is perhaps less suitable for use in outbreaks and more suited to use in a preventive vaccination program.

The United Nations International Children’s Emergency Fund will run a tendering process to buy vaccines for the stockpile, Berkley said. UNICEF is Gavi’s procurement agent for all the vaccines it helps countries purchase.

Berkley said $178 million has been budgeted for the Ebola program for the period of 2020 to 2025. “Now that funding has been approved, we will get to work with manufacturers and our Alliance partners to build the stockpile,” he said.

Vaccine doses for the stockpile will be stored by the manufacturers; they will be required to have on hand at all times the number of doses they were contracted to provide.

On a different matter, the Gavi board also agreed to continue support for three pilot projects currently underway in Kenya, Mali and Ghana to see if the world’s first malaria vaccine, RTS,S, is effective under real world conditions.

The vaccine, made by GSK, reduced malaria infections by about 40% in clinical trials — a substantial reduction given the scale of the devastation malaria wrecks.

But the vaccine is given in four doses — a difficult regimen under the best of circumstances. And in the countries where it is most needed, the timing of the doses does not always align with when children get other vaccinations or have scheduled health visits. The concern is that in the real world, children may not get all four doses, in which case the vaccine may not be able to deliver much benefit.

The pilot projects began in 2019 and are expected to run for four years.

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