THE HAGUE, Netherlands — European Union police agency Europol issued a warning Friday highlighting the risk of organized crime scams linked to COVID-19 vaccines, including the possibility criminals will try to sell dangerous counterfeit vaccines or to hijack shipments of genuine shots.

In an "early warning notification," Europol said that crime gangs already have reacted to opportunities presented by the coronavirus pandemic.

"Once a legitimate vaccine enters the market, counterfeited versions of the specific vaccine brand are expected to circulate rapidly," the agency's warning said, citing a phony flu vaccine that the World Health Organization discovered in Mexico in October.

"Similar to the fake influenza vaccine encountered in Mexico, counterfeit COVID-19 vaccines may represent a significant public health threat if they are ineffective at best or toxic at worst, given their production in underground labs without hygiene standards," Europol said. "Fake vaccines may even have a wider-reaching impact if new outbreaks emerge in communities assumed to be vaccinated."

The warning urged heightened vigilance by the EU's 27 member nations and other countries to "the possible involvement of criminals in the vaccine development and distribution process."

Europol said the "expected arrival of a genuine COVID-19 vaccine has already inspired criminal activities and will likely be exacerbated once vaccines become available."

The statement came after Britain gave emergency approval Wednesday to a vaccine produced by U.S. drugmaker Pfizer and Germany-based BioNTech, making Britain the first Western country to authorize a vaccine against the coronavirus. 

Europol, which is based in The Hague, said it was aware of criminals placing advertisements on dark web marketplaces "using the brands of genuine pharmaceutical companies that are already in the final stages of testing."

The police agency said criminal networks also could target the supply chain for genuine vaccines, such as by illegally refilling empty vials if they are not correctly disposed of or hijacking vehicles transporting shots.

It urged EU members to share with Europol "any relevant information on criminal activities related to COVID-19 or flu vaccines."