| Value | Category | 
                                    
                    
                        | 100 | No | 
                                    
                    
                        | 110 | Never had certificate | 
                                    
                    
                        | 120 | Had certificate | 
                                    
                    
                        | 121 | Vaccination dates recorded | 
                                    
                    
                        | 122 | Vaccination dates not recorded | 
                                    
                    
                        | 200 | Yes | 
                                    
                    
                        | 210 | Yes, seen | 
                                    
                    
                        | 211 | Vaccination dates recorded | 
                                    
                    
                        | 212 | Vaccination dates not recorded | 
                                    
                    
                        | 213 | Short certificate | 
                                    
                    
                        | 214 | Long certificate | 
                                    
                    
                        | 215 | Both long and short certificate | 
                                    
                    
                        | 220 | Yes, not seen | 
                                    
                    
                        | 997 | Don't know | 
                                    
                    
                        | 998 | Missing | 
                                    
                    
                        | 999 | NIU (not in universe) | 
                            
            Warning: these figures indicate the number of cases found in the data file. They cannot be interpreted as summary statistics of the population of interest.