Summary
Records of attempts to confer immunity to influenza by the use of vaccines have been separated into related groups and studied. Those where pure Pfeiffer strains were used have been considered in one group. Those where mixed vaccines were used have been analyzed in three sub-groups or series, depending on the relation between the times of vaccination and of the advent of the epidemic, upon whether or not a week-by-week comparison of the occurrence of influenza among vaccinated and unvaccinated groups was made, and upon whether or not statistics for total comparison alone were available. The third group included the reports of the use of army pneumo-lipovaccines for the prevention of the secondary pneumonia complications of influenza.
Conclusions
From our statistics we conclude that:
1. There is as yet no evidence that vaccines composed purely of strains of Pfeiffer bacilli will confer immunity to epidemic influenza.
2. The only data which can be used as a basis for estimating the value of mixed vaccines as a preventive for epidemic influenza must be obtained from experiments in which vaccination was either completed before the epidemic appeared, or in which week-by-week comparisons between the number of cases occurring in the vaccinated and unvaccinated groups can be made.
3. Data obtained from experiments conducted under the above qualifications is inconclusive, but presents little evidence of the value of mixed vaccines in protecting against influenza. There is, however, an indication that mixed vaccines used prior to the arrival of the epidemic will lessen the number and the severity of secondary pneumonias, and will probably lower the death rate to a small degree.
4. The army pneumo-lipovaccine apparently offers some protection against primary infections with types I, II and III pneumococci, and a somewhat lesser amount of protection against secondary pneumococcic infections with these strains following influenza.
5. While it is impossible to say that the large number of influenza cases developing almost immediately after vaccination would not have occurred anyway, it is at least suggestive that a temporary break occurs in the resistance after the inoculation, and that unusual care should be taken by persons who have been recently vaccinated, particularly when they are in the midst of an epidemic disease.