(Reuters) The Zika virus could spread to Africa, Asia and southern Europe, the World Health Organization said on Tuesday, as major French drug maker Sanofi SA and others joined the race to create a vaccine.

A day after Geneva-based WHO declared an international public health emergency due to Zika’s association with the birth defect microcephaly in Brazil, the United Nations agency said it had launched a global response unit to fight the mosquito-borne virus that is spreading rapidly in Latin America.

Babies born with microcephaly have abnormally small heads and improperly developed brains.

“Most important, we need to set up surveillance sites in low- and middle-income countries so that we can detect any change in the reporting patterns of microcephaly at an early stage,” Dr. Anthony Costello said in Geneva. Costello is WHO’s director for maternal, child and adolescent health.

Twenty to 30 sites could be established worldwide, mainly in poor countries without robust health care systems.

The Pan American Health Organization said Zika was now spreading in 26 countries and territories in the Americas.

The virus was first identified in 1947 in rhesus monkeys in Uganda while scientists were studying yellow fever, according to the World Health Organization. It was identified in humans in 1952. Zika virus is spread by mosquitoes of the Aedes genus.

There is no vaccine or treatment for it.

Sanofi’s announcement marked the most decisive commitment yet by a major vaccine producer to fight Zika. The company said its Sanofi Pasteur vaccines division would use its expertise in developing vaccines for similar viruses such as yellow fever, Japanese encephalitis and dengue.

“Sanofi Pasteur is responding to the global call to action to develop a Zika vaccine given the disease’s rapid spread and possible medical complications,” said Nicholas Jackson, research head of Sanofi Pasteur, who is leading the Zika vaccine project.