Division of Vital Statistics

Labrack, Edson K

Maine Department of Health and Welfare

English

Maine State Documents (Maine State Library)

Maine State Library Digital Maine Health & Human Services Documents Health & Human Services 6-1-1960 Paralytic Poliomyelitis Case Rates By Vaccine Status Aroostook County, Maine, 1959 Maine Department of Health and Welfare Division of Vital Statistics Edson K. Labrack Maine Department of Health and Welfare Follow this and additional works at: https://digitalmaine.com/dhhs_docs Recommended Citation Maine Department of Health and Welfare; Division of Vital Statistics; and Labrack, Edson K., "Paralytic Poliomyelitis Case Rates By Vaccine Status Aroostook County, Maine, 1959" (1960). Health & Human Services Documents. 32. https://digitalmaine.com/dhhs_docs/32 This Text is brought to you for free and open access by the Health & Human Services at Digital Maine. It has been accepted for inclusion in Health & Human Services Documents by an authorized administrator of Digital Maine. For more information, please contact statedocs@maine.gov. State Of MaineReprinted from the June I960 issue ofThe Journal of The Maine Medical AssociationDepartment of Health and WelfareParalytic Poliomyelitis Case Rates By Vaccine Status Aroostook County, Maine, 1959Ed so n  K. L a b r a c k , M .P.H .*When an outbreak of paralytic poliomyelitis oc­curred in Aroostook County, Maine, in 1959 it seemed desirable to attempt a special analysis to determine what effect inoculations with Salk poliomyelitis vaccine had had on the course of the outbreak.The Department of Health and Welfare conducted a sample survey in Aroostook County to gather data concerning the extent to which residents of the County had been inoculated with Salk vaccine. This study was described and the findings were presented in an earlier paper.1Data obtained in this survey made it possible to esti­mate poliomyelitis case rates by immunization status during the 1959 paralytic poliomyelitis outbreak in that County and to test certain hypotheses concerning the effect of this Salk vaccine in reducing the risk of con­tracting paralytic poliomyelitis. Case rates, or morbid­ity rates, were estimated from morbidity data obtained through the regular morbidity reporting channels of the Department and from estimates of the numbers of per­sons in the County by vaccine status survey.Morbidity DataSince Salk vaccine is presumed to be effective only in reducing the risk of paralytic disease, morbidity data used in the estimation of case rates were limited by re­moving from consideration any cases with a clinical diagnosis of poliomyelitis, but in which there was no residual paralysis apparent six months or more after the onset of the disease. The age group under 40 years of age was selected for analysis. This resulted in the1 Labrack, E.: Poliomyelitis immunization status in AroostookCounty, Maine, 1959, J. Maine Med. A. 51: 169, May, I960." D i r e c t o r ,  D i v i s i o n  o f  V i t a l  S t a t i s t i c s .elimination of one paralytic case who had received four inoculations with vaccine. Statistical tests indicate that the elimination of this case had no significant ef­fect on study findings. It was necessary to eliminate one other paralytic case since inoculation data concerning that individual was lacking. Laboratory confirmation of diagnoses would add to the precision of case rates. However, results of laboratory tests were not available at the time of analysis. Table 1 shows morbidity data used in the computation of case rates.TABLE 1Pa r a lytic  Po lio m y el it is  Ca ses b y  Age and  b y  V a c c in e  Sta tu sA ro o sto ok  Co u n t y , Ma in e , 1959Number of inoculations with vaccine 3 before 3 in 1958Total None 1 2 1958 or 19591 4Total ..................  49 28 5 5 7 2 2Under 1 ..........  1 —  1 —  —  —  —1- 4 ............  10 7 —  2 1 —  —5- 9 ............  13 7 3 1 2 —  —10-14 ................ 8 2 — 1 3  1 115-19 ................  4 1 —  i t  i —20-24 ............  2 2 —  —  —  —  _25-29 ............  5 4 1 —  —  —  —30-34 ............  4 4 —  —  —  —  —35-39 ............  1 1 —  —  —  — —40 and over .... 1 —  —  —  —  —  11 Prior to August 1, 1959.Paralytic Poliomyelitis Case R ates Paralytic poliomyelitis case rates by vaccine status in Aroostook County show differences which are substan­tially greater than one would expect to result from chance. Three distinct relationships are apparent: (1)The case rate appears to be related to the number of inoculations with vaccine. (2 ) The case rate appears to be related to the time elapsed since the last inocula­tion. (3 ) The case rate appears to be related to age.Tables 2 and 3 show the detail of case rate data for persons under 20 and for persons under 40 years of age.TABLE 2Estim ated  Po p u l a t io n . Paralytic  Po lio m y elitis  C a ses , Paralytic  Po lio m y el it is  Case  Ra tes by Va c cin e  Sta tu s  Per so n s  U n d er  20 Y ears o f  Age Aro o sto ok  Co u n t y , Ma in e , 1959Vaccine StatusParalytic Case rate Estimated Poliomyelitis per 10,000 Population Cases PopulationNo vaccine .................. 8,130 17 20.91 inoculation .............. 2,020 4 19.82 inoculations .............. 6,080 5 8.23 before 1958 ........... 7,170 7 9.83 in 1958 or 1959 .... 19,260 2 1.04 inoculations .............. 4,130 1 2.4TABLE 3Estim ated  Po p u l a t io n . Pa ralytic  Po lio m y elitis  Ca ses , Paralytic  Po lio m y el it is  Case  R ates by Va c cin e  Sta tu s  Per so n s  U n d er  40 Y ears o f Age Aro o sto o k  Co u n t y , M a in e , 1959Paralytic Case rate Estimated Poliomyelitis per 10,000Vaccine Status Population Cases PopulationNo vaccine .................. 18,760 28 14.91 inoculation .............. 4,000 5 12.52 inoculations .............. 8,650 5 5.83 before 1958 ........... 9,170 7 7.63 in 1958 or 1959 .... 25,130 2 0.84 inoculations .............. 5,190 i 2.0There appear to be three distinct levels in the case rates. (1 ) The case rate for persons who had received one inoculation with vaccine is not significantly dif­ferent from the case rate for persons who had received no vaccine. This would seem to indicate that one inoculation gives the recipient no significant protection.(2) The case rate for persons who had received a series of two inoculations is significantly lower than the case rate for persons who had received no vaccine or only one inoculation. This would seem to indicate that the second inoculation gives the recipient some protection.(3) The case rate for persons who had received aseries of three inoculations completed in 1958 or dur­ing the first seven months of 1959 was significantly lower than the case rate for persons who had received two inoculations. This would seem to indicate that a third inoculation gives significantly improved protection.(4 ) The case rate for persons who had received a series of four inoculations was not significantly differ­ent from the case rate for persons who had received a third inoculation with vaccine during 1958 or during the first seven months of 1959. This would seem to indicate that the third inoculation confers optimal im­munity.(5 ) The case rate for persons who had received a third inoculation with vaccine in 1958 or during the first seven months of 1959 was significantly lower than the case rate for persons who had received a third in­oculation before 1958. This would seem to indicate that the immunity conferred by a course of three inocula­tions wanes significantly after about a year and that a booster inoculation is necessary to restore immunity to an optimal level. The number of cases among persons with three inoculations with vaccine during 1958 and 1959 was small and it was not possible to determine from study data the point at which the immunity gained through a series of three inoculations had waned to a significant degree. However, the fact that the case rate was significantly higher among persons who had re­ceived a series of three inoculations completed prior to 1958 seems to indicate that immunity has waned signifi­cantly by the end of the second year after the comple­tion of the series.(6 ) The case rate for all persons under 20 years of age whose immunization level was less than optimal was approximately twice as great as the case rate in the comparable population of persons 20-39 years of age.Summary and ConclusionA study of case rates during an outbreak of paralytic poliomyelitis in Aroostook County, Maine, in 1959 con­firms the effectiveness of Salk vaccine in reducing the risk of paralytic poliomyelitis. Significant findings of the study indicate that it is probably safe to conclude that persons who have received 2 inoculations from Salk vac­cine have some degree of protection against poliomye­litis and that the degree of protection is increased by a third inoculation. The immunity gained by a course of 3 inoculations with Salk vaccine appears to wane after a period of time and booster inoculations are needed to restore immunity to an optimal level.

Paralytic Poliomyelitis Case Rates By Vaccine Status Aroostook County, Maine, 1959

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Paralytic Poliomyelitis Case Rates By Vaccine Status Aroostook County, Maine, 1959

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