US pharmaceutical company Pfizer says it has identified counterfeit versions of its coronavirus vaccine in Mexico and Poland.
The doses were seized by authorities in the two countries and confirmed by tests to be fake.
In Mexico, they had false labels, while the substance in Poland was believed to be anti-wrinkle treatment, Pfizer said.
The World Health Organization (WHO) has warned that fake vaccines "pose a serious risk to global public health".
It has called for them to be identified and removed from circulation.
Poland's health minister on Wednesday stressed that the risk of counterfeit doses appearing in official circulation was "practically non-existent".