These findings also correspond with our previously recorded conclusion made after studying the disease incidence with three increasing degrees of exposure, _sleep_, _room_ and _family_ (page 198). TABLE IX. _Comparison of the severity of the first and second attacks in individuals contracting influenza in 1918–19 and again in 1920._ ═════════════════════════════╤═════════════╤═════════════╤═════════════ Severity. │No. of cases.│ Comparison. │No. of cases. ──────────────┬──────────────┼─────────────┼─────────────┼───────────── 1918–19. │ 1920. │ „ │ „ │ „ ──────────────┼──────────────┼─────────────┼─────────────┼───────────── Average │Mild │ 43│Second attack│ 132 │ │ │ milder │ Severe │Mild │ 50│ „ │ „ Severe │Average │ 39│ „ │ „ ──────────────┼──────────────┼─────────────┼─────────────┼───────────── Mild │Mild │ 30│Both of equal│ 72 │ │ │ severity │ Average │Average │ 22│ „ │ „ Severe │Severe │ 20│ „ │ „ ──────────────┼──────────────┼─────────────┼─────────────┼───────────── Mild │Average │ 13│ Second more │ 36 │ │ │ severe │ Mild │Severe │ 5│ „ │ „ Average │Severe │ 18│ „ │ „ ──────────────┴──────────────┴─────────────┴─────────────┴───────────── Altho we find no conclusive evidence of protection against recurrent attacks, we do find (Table IX) that the second attack in the same individual was usually milder. However, the 1920 epidemic as a whole was milder, (Chart XVIII). Zinsser quotes a letter from Frost in which the latter states that in Baltimore those persons who were attacked during the 1918–19 epidemic showed no relative immunity during the epidemic of 1920. This is not a contradiction to the earlier Baltimore studies, since in that case the interval between the epidemic waves was not more than about three months.