A mosquito-borne virus suspected of causing brain damage in babies has spread to 21 countries.

Researchers say developing a vaccine for the Zika virus could take up to five years, as health experts called for new incentives for drug companies.

The Zika outbreak, which the World Health Organisation says is likely to spread to all countries in the Americas except for Canada and Chile, follows the Ebola epidemic in West Africa, which also caught health authorities off guard.

“We’ve got no drugs and we’ve got no vaccines. It’s a case of deja vu because that’s exactly what we were saying with Ebola,” Trudie Lang, a professor of global health at Oxford University, told Reuters. “It’s really important to develop a vaccine as quickly as possible.”

Large drugmakers’ investment in tropical disease vaccines with uncertain commercial prospects has so far been patchy, but the pace of the outbreak has demonstrated how quickly little-known diseases can emerge as global threats.

“We need to have some kind of a plan that makes [companies] feel there is a sustainable solution and not just a one-shot deal over and over again,” Francis Collins, director of the US National Institutes of Health, said last week.

The Sao Paulo-based Butantan Institute, which is currently leading the research on Zika, says it plans to develop a vaccine “in record time”, although its director has said this is likely to take three to five years.

British drugmaker GlaxoSmithKline also told Reuters on Monday that it was studying the feasibility of using its vaccine technology on Zika, while France’s Sanofi said it was reviewing possibilities.

Brazil’s Health Ministry in November announced that it suspected that links existed between the mosquito-borne Zika virus and a foetal deformation, known as microcephaly, in which infants are born with smaller-than-usual brains.

The WHO has described circumstantial evidence of the link as “suggestive and extremely worrisome.”

Brazil has reported 3,893 suspected cases of microcephaly, the WHO said last Friday, more than 30 times more than had been reported in any year since 2010.

The outbreak has prompted El Salvador, Eduador and Colombia to warn women to delay getting pregnant.

The disease’s rapid spread to 21 countries and territories of the region since May 2015 is caused by a lack of immunity among the population and the prevalence of the Aedes aegypti mosquito that carries the virus, the WHO said.

The pace of the outbreak prompted Margaret Chan, the WHO's director-general, to call for changes in how the organisation responds to emergencies.

“The complexity of humanitarian emergencies underscores the need for transformational changes in our response capacity,” she said.

•Adapted from an Al Jazeera report. Photo courtesy of AP shows A Brazilian mother bathing her son, who has been diagnosed with microcephaly, in a bucket of water, to help calm him.

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