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 Fears of a widening outbreak of the mosquito-borne disease were
fuelled this week by a spike in cases in the Democratic Republic of
Congo (DRC), which now says it has seen more than 1,000 suspected
cases since March.
"Experts agreed to propose if necessary, if there is a shortage of
vaccine, to divide the vaccine by five," WHO spokesman Tarik
Jasarevic said on Friday, reporting on a meeting this week.
"One fifth of a dose according to their evidence would be sufficient
to provide immunity for at least 12 months."
Reuters previously reported that a move to stretch vaccine supplies
in this was likely.
The normal full dose of the vaccine confers life-long protection and
the WHO emphasised that the low dose endorsed by its independent
experts was designed specifically for emergency mass vaccination,
not for routine immunisation.
More research is also needed to see if low doses will work for young
children, who may have a weaker immune response, and practical
challenges remain over obtaining the right syringes.
The current yellow fever epidemic started in Angola but a major
outbreak in the DRC's capital city of Kinshasa, which has a
population of more than 12 million, is a big worry for healthcare
officials.
The global stockpile of yellow fever vaccines has already been
depleted twice this year to immunize people in Angola, Uganda and
the DRC. It currently stands at 6 million doses but this may not be
enough if there are simultaneous outbreaks in multiple densely
populated areas.
Almost 18 million doses have been distributed for emergency
vaccination campaigns so far in the three African countries.
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Concerns about limited vaccine supplies have been building for some
time, with a group of medics calling for low-dose use in an article
in The Lancet journal back in April.
Yellow fever is transmitted by the same mosquitoes that spread the
Zika and dengue viruses, although it is a much more serious disease.
The "yellow" in the name refers to the jaundice that affects some
patients.
Although approximately 6 million vaccine doses are kept in reserve
for emergencies, there is no quick way to boost output when there is
a surge in demand since production, using chicken eggs, takes around
12 months.
Manufacturers include the Institut Pasteur, government factories in
Brazil and Russia, and French drugmaker Sanofi.
The current outbreak of yellow fever was first detected in Angola in
late December 2015.
(Editing by Alison Williams and Dominic Evans)
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