As the world reopens after a year-long pandemic blockade, many restaurants, workplaces, event venues, and even some countries are requiring customers to show proof of COVID-19 vaccination before entering.

There is just one major problem. Fake vaccination certificates are surprisingly easy to buy online or make yourself.

According to Check Point, an Israeli security company, fake U.S. and Russian vaccination certificates are being sold online for $100 to $200. Fake COVID-19 negative test results cost only $25, and (supposedly fake) COVID-19 vaccines sell for about $500 per vial.

But honestly, if you are paying $150 for a fake vaccination card in the US, you are being ripped off. The official Centers for Disease Control COVID-19 vaccination record cards that you get when you get vaccinated in the US are ridiculously easy to forge.

All you need is a PDF of a blank card, a decent home printer, and a medium thickness of card stock. Now that we know this, we don't trust the CDC vaccination card to be used as a "pass" to enter places where only vaccinated people are allowed.

Images of actual CDC cards can be easily found online. The official website of at least one U.S. state has a blank version of the card in printer-ready PDF format that can be downloaded.

To make a fake CDC vaccination card convincing, you need to know what information to write (by hand, just like on a real card).

However, I found a PDF online with examples of not only blank immunization cards, but also how to print them, the name of the vaccine product, the manufacturer, the lot number, and the immunization provider that makes them convincing.

"This document does not stand up to digital scrutiny," the instructions caution. At best, it will pass police and military checkpoints."

In reality, CDC cards are accepted in several places. Iceland now accepts CDC cards as proof of immunization. In other words, any rascal can travel to the land of hot springs by printing and filling out a convincing fake card.

Other countries, including Belize, Cyprus, Estonia, Greece, Guatemala, Poland, Portugal, and Romania, require proof of vaccination to enter without quarantine, but it is not clear exactly what proof is required. (Also, if you present your CDC vaccination card, you will receive a free Krispy Kreme doughnut.

"What these little cards could do is make things like international travel easier by bypassing the need for quarantine and testing," one infectious disease expert told ABC News in a recent report.

Many other countries are waiting to develop digital "vaccine passports" that are not so easy to forge before allowing people into their countries. The "passport" would likely take the form of a smartphone app that displays a QR code that can be presented at border checkpoints.

However, fake digital certificates showing negative COVID test results are already being trafficked: in November, French police busted a group selling fake negative test results to travelers at Paris' Charles de Gaulle airport.

The creators of the ready-to-print CDC fake vaccination card PDF promise that "if a digital 'passport' system becomes available, we will reverse engineer it too, so that it can be found just as easily as we found this document."

Their logic is admirable from an American-oriented point of view, but incredibly stupid from a medical point of view. [33] [34] "We simply believe that no American should be prevented from working, getting food, accessing property, or visiting loved ones," the card forgers declare.

If there are significant numbers of people who refuse to be vaccinated with the COVID-19 vaccine or who cannot be vaccinated for other reasons, then there is sure to be a demand for fake vaccination certificates.