But researchers from MIT might have a solution: they've created an ink that can be safely embedded in the skin alongside the vaccine itself, and it's only visible using a special smartphone camera app and filter.

In other words, they've found a covert way to embed the record of a vaccination directly in a patient's skin rather than documenting it electronically or on paper - and their low-risk tracking system could greatly simplify the process of maintaining accurate vaccine records, especially on a larger scale.

"In areas where paper vaccination cards are often lost or do not exist at all, and electronic databases are unheard of, this technology could enable the rapid and anonymous detection of patient vaccination history to ensure that every child is vaccinated," researcher Kevin McHugh said in a statement.