The warning comes as the U.S. is close to approving Pfizer’s vaccine.

As the United States inches closer to Food and Drug Administration approval of a COVID-19 vaccination, the FBI is warning Americans of potential vaccine fraud.

FBI Washington Field Office Assistant Special Agent in Charge Timothy Thibault told ABC News that there could initially be issues in distributing the vaccine and that scammers will use this to their advantage.

“What we would say to the public is to be leery of and be on guard for scams related to telemarketing, malicious websites or emails where people are taking advantage of the initial supply-and-demand problem,” Thibault said.

In October, the World Health Organization found a fake flu vaccine in Mexico, according to EUROPOL, the European Union’s law enforcement arm. EUROPOL worries the same could happen with the COVID-19 vaccine.

“The same scenario is also likely to happen when COVID-19 vaccines do become available,” the agency said in a press release. “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.”

Specifically, Thibault stressed that there will “certainly” be bad actors looking to take advantage of people during the rollout of the vaccine.

“Bad actors will reach out to people and may take advantage of their desperation to get the vaccine early,” he said.

Thibault warned no American should have to pay for the vaccine — and anyone telling them to do so is wrong.

He also said that these scams will need to be carried out quickly as more of the legitimate vaccines flood the country.

“The fraudsters have to know that these types of scams, with regard to the vaccine, have a time limit on them,” he said.

The assistant special agent in charge also mentioned that people are often embarrassed to admit they were the victim to this type of fraud, but he urged victims to tell law enforcement in order to stop future incidents.

“These are crimes of greed and opportunity,” Thibault said.