The CDC cards are currently the only way to prove you've received a COVID vaccine, so Staples is laminating them for free

• Staples will laminate vaccine cards for free through May 1.
• Experts recommend keeping the card in a safe place because it's the main proof of vaccination.
• Some countries are working on digital records, but the US has no clear plans.

Millions of Americans who have been vaccinated against COVID-19 are carrying around paper cards as their only proof. Staples is offering free lamination of vaccine cards around the country to help with safekeeping.

Cards can be laminated after the holder receives the second dose, for vaccines that require two doses, Staples told Insider. The offer is valid through May 1, an extension from the earlier April 3 date.

Other businesses are offering their own perks to encourage vaccination. Krispy Kreme is giving out free donuts to anyone with a vaccination card. Target and Dollar General are two of many offering vacation time for vaccine appointments. Kroger, Petco, and Publix are all offering cash or gift cards to employees who show proof of vaccinations.

Read more: Is it a crime to give away leftover COVID shots? Doctors and other healthcare workers fear legal consequences as they wait for Justice Department guidance.

The small paper cards are issued by the CDC at the point of vaccination and serve as a reminder to come back for the second dose of Moderna or Pfizer shots. Because the government agency isn't keeping track of who gets vaccinated, the cards also act as proof of vaccination, Insider's Allana Akhtar reported. The CDC recommends taking a photo of the card as a backup in case it gets lost or damaged.

Vaccine cards are likely to become increasingly important as more people are inoculated and the world begins to open back up. Proof of vaccination may be required for airlines, international travel, and returning to work and schools.

Digital vaccine passports are catching on in some parts of the world. The European Commission proposed a digital certificate that would allow travel within the EU as early as this summer, and Israel and China each have their own versions of digital passports.

In the US, people who receive vaccines at Walmart and Sam's Club can soon access a digital passport called CommonPass, but there's no cohesive national passport yet so it's important to keep the card safe.