Table 2. Example for the identification of live-attenuated influenza vaccine Fluenz Tetra vaccination records with a single known lot number of FJ2098C using the Levenshtein string similarity metric [16] and a similarity value ≥ 0.7 as an approximate match.

Lot number	Cleansed lot number	Similarity value	Trade name	Vaccine identified by
LOT FJ2098C	FJ2098C	(not evaluated)	(not evaluated)	Lot number, exact match
F72098C	F72098C	0.857	(not evaluated)	Lot number, fuzzy match
fj2098.	FJ2098	0.857	(not evaluated)	Lot number, fuzzy match
FJ2O98	FJ2O98	0.714	(not evaluated)	Lot number, fuzzy match
FJ20	FJ20	0.571	Fluenz Tetra	Trade name, exact match
Fluenz Tetra	FLUENZTETRA	0.091	(missing value)	(not identified)

The default variable for identifying the administered vaccine is the lot number, cleansed for potential spelling mistakes. If this identification process fails, the trade name is evaluated. Having valuable information, e.g. the trade name, entered in the wrong field and other fields, e.g. the actual field for the trade name, empty or also with the wrong kind of information, can make the vaccine identification as part of the record linkage impossible.