Empty values in numdays field

• Each row in the DATA CSV file has an entry for VAX_DATE (date of vaccination) and ONSET_DATE (date of first symptom onset)
• If one of these is not provided, then the NUMDAYS field (which is the difference between them) cannot be calculated
• sometimes, both of these dates are provided but the value of NUMDAYS is empty
• this is because if the onset date is not known but the onset month is known, the date is automatically recorded as the first of the month
• this means sometimes the ONSET_DATE is before the VAX_DATE!
  • and obviously the NUMDAYS cannot be calculated
• but there is still enough information to make some inferences

Example of report where NUMDAYS is available

Example of report where NUMDAYS is empty