NFC blocking sleeves lined with a metallic material that will block the NFC signal. Dimensions suitable for miniOTP cards / 64 × 38 mm

There isn't a way to extract the secret from the card, but it is theoretically possible to read the current OTP and the serial number.  Although the risk of replay attacks is practically close to zero, you can physically isolate your programmable tokens by keeping them inside the NFC blocking sleeves.