A new outbreak of Zika virus is quite possible, warn researchers, with a single mutation potentially enough to trigger an explosive spread.
The disease caused a global medical emergency in 2016, with thousands of babies born brain-damaged after their mums became infected while pregnant.
US scientists say the world should be on the lookout for new mutations.
Lab work, described in the journal Cell Reports, suggests the virus could easily shift, creating new variants.
Recent infection studies suggest those variants may prove effective at transmitting the virus, even in countries which have built up immunity from previous outbreaks of Zika, say the team from the La Jolla Institute for Immunology.
Experts said the findings, although theoretical, were interesting – and a reminder that viruses other than Covid could pose a threat.
Zika is spread by bites from infected Aedes mosquitoes. The insects are found throughout the Americas – except for Canada and Chile, where it is too cold for them to survive – and across Asia.
While for most people Zika is a mild illness, with no lasting effects, it can have catastrophic consequences for babies in the womb.
If a mother contracts the virus during pregnancy, it can harm the developing baby, causing microcephaly (unusually small head) and damaged brain tissue.