| Value | Category | 
                                    
                    
                        | 0 | No doses | 
                                    
                    
                        | 2001 |  | 
                                    
                    
                        | 2002 |  | 
                                    
                    
                        | 2003 |  | 
                                    
                    
                        | 2004 |  | 
                                    
                    
                        | 2005 |  | 
                                    
                    
                        | 6666 | No card and DK | 
                                    
                    
                        | 9998 | Card but DK | 
                                    
                    
                        | Sysmiss |  | 
                            
            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.