PUBLIC HEALTH BRIEFS
Berry,2 in her study of U.S. maternal mortality, suggested that age and parity distributional changes had some influence on maternal mortality rates, even during an era of rapid overall decline. Her finding reinforces the position that "the frequency and timing of births must be regulated if maternal mortality is to be brought to an irreducible minimum." 2
REFERENCES 1. Springett VH: A comparative study of tuberculosis mortality rates. J of Hygiene 48:361-395, 1950.
2. Berry LG: Age and parity influences on maternal mortality: United States, 1919-1969. Demography 14:297-310, 1977.
ACKNOWLEDGMENTS The author wishes to thank Vito M. Logrillo, Phillip R. Quickenton and Michael A. Ellrott for their highly significant contributions at all stages of the research process. This research was supported in part by National Center for Health Statistics Contract No.
HRA-230-77-0066.
Vaccine Failures in the Epidemiology And Control of Measles MARC A. STRASSBURG, MPH, SANDER GREENLAND, DRPH, MS, AND SHIRLEY L. FANNIN, MD
Abstract: Data were employed from confirmed measles case reports and an immunization survey to estimate the apparent effectiveness of measles vaccine in Los Angeles County in 1976. We evaluated the age-specific proportions of our case load arising from persons erroneously thought to possess immunity. Thirty five per cent of our cases claimed to have had prior measles vaccination, and over 60 per cent of these reported having written records. Since community measles control programs rely on immunization records as the principal screening tool, the shortcomings observed need to be recognized. (Am J Public Health 69:1055-1056, 1979.)
Introduction Measles vaccine has generally been accepted as being safe and highly effective. Under ideal field trial conditions, single inoculations of live attenuated measles virus vaccine induced seroconversion in more than 95 per cent of vaccinees."' 2 However, later reports have questioned the efficacy of vaccine used under community field conditions.3 In documented outbreaks cases have occurred among persons previously vaccinated with live measles vaccine.4 5 Several explanations for these reported "measles vaccine failures" have been suggested, including: vaccination at less than one year of age, administration of reduced potency vaccine, waning immunity, immunological deficiencies in the host, Address reprint requests to Marc A. Strassburg, MPH, Epidemiology Analyst/Acute Communicable Disease Control, County of Los Angeles, Department of Health Services, 313 North Figueroa Street, Los Angeles, CA 90012. Dr. Greenland is Assistant Professor of Biostatistics, Harvard School of Public Health; Dr. Fannin is Chief, Acute Communicable Disease Control, LA County Dept. of Health Services. This paper, submitted to the Journal October 2, 1978, was revised and accepted for publication April 3, 1979. AJPH October 1979, Vol. 69, No. 10
vaccine administered with gamma globulin, or poor antigenicity of the vaccine. This paper discusses vaccine failures and vaccine reports in the epidemiology and control of measles in Los Angeles County.
Methods and Procedures During the 1973-1976 epidemiologic years,* 1,733 suspected cases of measles were reported to the Los Angeles County Department of Health Services and were investigated by public health nurses. For each case, demographic variables, disease manifestations, disease history, vaccine history, possible source(s) of infection, and primary and secondary contacts were obtained. Clinical criteria for a diagnosis of measles were: general rash of about four days; fever of at least 101°F; and one or more of the following symptoms: cough, runny nose, red eyes, or eyes sensitive to light. Measles serologies were performed on only a small number of cases. To assess attack rates by vaccination status, the Immunization Project's survey of 1974 was used.** The survey characterized the population's immune status one year before the start of the 1976 epidemiologic year.
*An epidemiologic year begins on week 41 of one calendar year and extends to week 40 of the following calendar year. The 1976 epidemiologic year was therefore October 1975-September 1976. **Unpublished report: Los Angeles County Immunization Survey 1974, Immunization Project, Bureau of Epidemiology, Los Angeles County Health Services Department, August 15, 1974. This was a household survey conducted on a random sample of children living within each of the County's five Health Services Regions. Eighty-eight per cent of those sample were successfully interviewed.
1055
PUBLIC HEALTH BRIEFS TABLE 1-Reported Measles Cases 1973-1976 EpIdemIologic Years 1973
Cases confirmed as rubeola* Cases confirmed as other diseases (e.g., rubella, scarlet fever) Unknown TOTALS
1974
1975
113 (51)
135 (66)
85 (61)
94 (43) 13 (6) 220 (100)
61 (30) 10 (5) 206 (101)**
41(30) 13 (9) 139 (100)**
1976
934 (80) 128 (11) 106 (09) 1168 (100)
*Confirmed by clinical criteria
"Round-off error Percentage shown in parentheses
Results
risk for the numbers of persons at risk in the rate denominators. For each age group, our 1976 measles reports provided the numbers of cases observed and case vaccine histories, while the 1974 immunization survey provided the proportion of unvaccinated susceptibles and the proportion vaccinated. In order to justify our estimate, we must assume the 1974 survey results approximated the immunity status of our population in the fall of 1975. This assumption seems reasonable, since no measles epidemic or vaccination campaign occurred between the 1974 and 1976 epidemiologic years. Table 3 displays the results of the immunization survey and the PR calculations in three childhood age groups. As an example of the interpretation of the PR, for the 1-4 year olds, the PR of 8.4 indicates that unvaccinated children in the population were at 8.4 times greater risk of contracting measles than were vaccinated children.*** It is worth examining the sensitivity of our PR estimate to errors in estimating the proportions of unvaccinated individuals in our population. (Such errors could be caused, for example, by the rapid flux in the immigrant population in Los Angeles.) If the proportion unvaccinated among the 1-4 year olds in 1976 had been .30 rather than .25, the PR would have been 7.0 rather than 8.4. The decline in the PR with in-
Table 1 shows the pattern of confirmed measles cases among the reported cases. It is suspected that reported cases represent only a small fraction of actual cases. Age, sex, and ethnic infqrmation varied little over the study period or between vaccinees and nonvaccinees. No statistically significant differences in symptomatology were observed between vaccinees and nonvaccinees in 1976. Table 2 presents reported vaccination status by age for the 1976 cases. With regard to the validity of the vaccine histories, cases were examined by source of vaccine history. In 1976, 63 per cent of the cases reporting prior vaccination reported having some form of written immunization record. It should be borne in mind that the remaining reports (those not documented) are subject to considerable error. The figures in Table 2 were combined with information from the immunization survey in Los Angeles County to arrive at an estimated protection ratio (PR), a form of relative risk: Number of cases observed with no vaccine history Proportion of unvaccinated susceptibles in the population
PR = Number of cases observed with a vaccine history Proportion of vaccinated persons in population with no prior history of measles
***Given that a population group with no prior history of disease is challenged with the wild virus, if 100 per cent of the unvaccinated and 5 per cent of the vaccinated contract the disease, then the expected PR would be 20 or greater (as in some of the early field trials).7
Because it is a ratio of risks, the PR can be estimated from our data by simply substituting the proportions of persons at
TABLE 2-Vaccination Status by Age for Confirmed Measles Cases, 1976 EpidemIologI Year Age Groups (Years)
Vaccine History
None Live Live&GG* Killed Unspecified type of vaccine TOTALS
Berry,2 in her study of U.S. maternal mortality, suggested that age and parity distributional changes had some influence on maternal mortality rates, even during an era of rapid overall decline. Her finding reinforces the position that "the frequency and timing of births must be regulated if maternal mortality is to be brought to an irreducible minimum." 2
REFERENCES 1. Springett VH: A comparative study of tuberculosis mortality rates. J of Hygiene 48:361-395, 1950.
2. Berry LG: Age and parity influences on maternal mortality: United States, 1919-1969. Demography 14:297-310, 1977.
ACKNOWLEDGMENTS The author wishes to thank Vito M. Logrillo, Phillip R. Quickenton and Michael A. Ellrott for their highly significant contributions at all stages of the research process. This research was supported in part by National Center for Health Statistics Contract No.
HRA-230-77-0066.
Vaccine Failures in the Epidemiology And Control of Measles MARC A. STRASSBURG, MPH, SANDER GREENLAND, DRPH, MS, AND SHIRLEY L. FANNIN, MD
Abstract: Data were employed from confirmed measles case reports and an immunization survey to estimate the apparent effectiveness of measles vaccine in Los Angeles County in 1976. We evaluated the age-specific proportions of our case load arising from persons erroneously thought to possess immunity. Thirty five per cent of our cases claimed to have had prior measles vaccination, and over 60 per cent of these reported having written records. Since community measles control programs rely on immunization records as the principal screening tool, the shortcomings observed need to be recognized. (Am J Public Health 69:1055-1056, 1979.)
Introduction Measles vaccine has generally been accepted as being safe and highly effective. Under ideal field trial conditions, single inoculations of live attenuated measles virus vaccine induced seroconversion in more than 95 per cent of vaccinees."' 2 However, later reports have questioned the efficacy of vaccine used under community field conditions.3 In documented outbreaks cases have occurred among persons previously vaccinated with live measles vaccine.4 5 Several explanations for these reported "measles vaccine failures" have been suggested, including: vaccination at less than one year of age, administration of reduced potency vaccine, waning immunity, immunological deficiencies in the host, Address reprint requests to Marc A. Strassburg, MPH, Epidemiology Analyst/Acute Communicable Disease Control, County of Los Angeles, Department of Health Services, 313 North Figueroa Street, Los Angeles, CA 90012. Dr. Greenland is Assistant Professor of Biostatistics, Harvard School of Public Health; Dr. Fannin is Chief, Acute Communicable Disease Control, LA County Dept. of Health Services. This paper, submitted to the Journal October 2, 1978, was revised and accepted for publication April 3, 1979. AJPH October 1979, Vol. 69, No. 10
vaccine administered with gamma globulin, or poor antigenicity of the vaccine. This paper discusses vaccine failures and vaccine reports in the epidemiology and control of measles in Los Angeles County.
Methods and Procedures During the 1973-1976 epidemiologic years,* 1,733 suspected cases of measles were reported to the Los Angeles County Department of Health Services and were investigated by public health nurses. For each case, demographic variables, disease manifestations, disease history, vaccine history, possible source(s) of infection, and primary and secondary contacts were obtained. Clinical criteria for a diagnosis of measles were: general rash of about four days; fever of at least 101°F; and one or more of the following symptoms: cough, runny nose, red eyes, or eyes sensitive to light. Measles serologies were performed on only a small number of cases. To assess attack rates by vaccination status, the Immunization Project's survey of 1974 was used.** The survey characterized the population's immune status one year before the start of the 1976 epidemiologic year.
*An epidemiologic year begins on week 41 of one calendar year and extends to week 40 of the following calendar year. The 1976 epidemiologic year was therefore October 1975-September 1976. **Unpublished report: Los Angeles County Immunization Survey 1974, Immunization Project, Bureau of Epidemiology, Los Angeles County Health Services Department, August 15, 1974. This was a household survey conducted on a random sample of children living within each of the County's five Health Services Regions. Eighty-eight per cent of those sample were successfully interviewed.
1055
PUBLIC HEALTH BRIEFS TABLE 1-Reported Measles Cases 1973-1976 EpIdemIologic Years 1973
Cases confirmed as rubeola* Cases confirmed as other diseases (e.g., rubella, scarlet fever) Unknown TOTALS
1974
1975
113 (51)
135 (66)
85 (61)
94 (43) 13 (6) 220 (100)
61 (30) 10 (5) 206 (101)**
41(30) 13 (9) 139 (100)**
1976
934 (80) 128 (11) 106 (09) 1168 (100)
*Confirmed by clinical criteria
"Round-off error Percentage shown in parentheses
Results
risk for the numbers of persons at risk in the rate denominators. For each age group, our 1976 measles reports provided the numbers of cases observed and case vaccine histories, while the 1974 immunization survey provided the proportion of unvaccinated susceptibles and the proportion vaccinated. In order to justify our estimate, we must assume the 1974 survey results approximated the immunity status of our population in the fall of 1975. This assumption seems reasonable, since no measles epidemic or vaccination campaign occurred between the 1974 and 1976 epidemiologic years. Table 3 displays the results of the immunization survey and the PR calculations in three childhood age groups. As an example of the interpretation of the PR, for the 1-4 year olds, the PR of 8.4 indicates that unvaccinated children in the population were at 8.4 times greater risk of contracting measles than were vaccinated children.*** It is worth examining the sensitivity of our PR estimate to errors in estimating the proportions of unvaccinated individuals in our population. (Such errors could be caused, for example, by the rapid flux in the immigrant population in Los Angeles.) If the proportion unvaccinated among the 1-4 year olds in 1976 had been .30 rather than .25, the PR would have been 7.0 rather than 8.4. The decline in the PR with in-
Table 1 shows the pattern of confirmed measles cases among the reported cases. It is suspected that reported cases represent only a small fraction of actual cases. Age, sex, and ethnic infqrmation varied little over the study period or between vaccinees and nonvaccinees. No statistically significant differences in symptomatology were observed between vaccinees and nonvaccinees in 1976. Table 2 presents reported vaccination status by age for the 1976 cases. With regard to the validity of the vaccine histories, cases were examined by source of vaccine history. In 1976, 63 per cent of the cases reporting prior vaccination reported having some form of written immunization record. It should be borne in mind that the remaining reports (those not documented) are subject to considerable error. The figures in Table 2 were combined with information from the immunization survey in Los Angeles County to arrive at an estimated protection ratio (PR), a form of relative risk: Number of cases observed with no vaccine history Proportion of unvaccinated susceptibles in the population
PR = Number of cases observed with a vaccine history Proportion of vaccinated persons in population with no prior history of measles
***Given that a population group with no prior history of disease is challenged with the wild virus, if 100 per cent of the unvaccinated and 5 per cent of the vaccinated contract the disease, then the expected PR would be 20 or greater (as in some of the early field trials).7
Because it is a ratio of risks, the PR can be estimated from our data by simply substituting the proportions of persons at
TABLE 2-Vaccination Status by Age for Confirmed Measles Cases, 1976 EpidemIologI Year Age Groups (Years)
Vaccine History
None Live Live&GG* Killed Unspecified type of vaccine TOTALS
