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Status Report on the Childhood Immunization Initiative: Reported Cases of Selected Vaccine-Preventable Diseases -- United States, 1996

The Childhood Immunization Initiative (CII), a comprehensive response to undervaccination among preschool-aged children, was initiated in the United States in 1993 (1). The goals of the CII were to eliminate by 1996 indigenous cases of diphtheria, tetanus (among children aged less than 15 years), poliomyelitis, Haemophilus influenzae type b (Hib) invasive disease (among children aged less than 5 years), measles, and rubella (1); reduce indigenous cases of mumps to less than 1600; and increase vaccination coverage levels to greater than or equal to 90% among children aged 2 years for the most critical doses of each vaccine routinely recommended for children (except hepatitis B vaccine). This report presents provisional 1996 data about reported cases of selected vaccine-preventable diseases. * In 1996, no cases of tetanus among children aged less than 15 years or of polio caused by wild poliovirus were reported in the United States; the number of reported cases of indigenously acquired mumps was substantially below the disease-reduction target; and the numbers of reported cases of diphtheria, invasive Hib disease (among children aged less than 5 years), rubella, and measles were at or near the lowest levels ever recorded and near the elimination targets.

The occurrence of notifiable diseases, including diphtheria, tetanus (among children aged less than 15 years), pertussis, polio caused by wild poliovirus, measles, rubella, and invasive Hib disease (among children aged less than 5 years), in the 50 states, New York City, and the District of Columbia is monitored by the National Notifiable Diseases Surveillance System (NNDSS), supplemented by data from other surveillance systems. Cases reported to NNDSS as indigenous or unknown were classified as indigenous cases. For measles and rubella, only cases classified as confirmed or of unknown case status because of missing information are included. NNDSS reports for diphtheria and invasive disease caused by Hib are supplemented by additional data from other sources. Hib cases reported to NNDSS include cases of invasive disease caused by serotype b and unknown serotypes among children aged less than 5 years. These data are supplemented by cases reported to the National Bacterial Meningitis and Bacteremia Reporting System (NBMBRS) and by laboratory-based active surveillance, both conducted by CDC. Probable and confirmed diphtheria cases with onset in 1996 reported to CDC's National Immunization Program (NIP) but not to NNDSS are included. All 1996 data are provisional. Because of the lack of comparable baseline data for indigenously acquired cases, total cases reported to NNDSS are presented for 1988-1992.

Overall, five states achieved all six 1996 CII disease-elimination goals, 10 states achieved five goals, 23 achieved four goals, and 12 achieved three goals. The District of Columbia and New York City achieved six and two disease-elimination goals, respectively.

Polio and tetanus. Since 1979, no indigenously acquired cases of polio caused by wild poliovirus have been reported in the United States (3). Of the 36 cases of tetanus reported in 1996, none occurred among children aged less than 15 years.

Measles. A provisional total of 443 indigenously acquired and 65 imported cases of measles were reported to the NNDSS. Of the 440 indigenously acquired cases for which data were available, 109 (25%) occurred among children aged less than 5 years and 148 (34%), among persons aged greater than or equal to 20 years. Of the 443 cases for which data were available, 325 (73%) were epidemiologically or virologically linked to imported cases. The number of indigenously acquired measles cases reported in 1996 represents a 22-fold decline from the median number reported during the 5 years preceding initiation of the CII in 1993 (Table_1). Epidemiologic and virologic data suggest that indigenous measles transmission in the United States has been repeatedly interrupted, followed by reintroduction of imported measles virus (4). During an 8-week period in late 1996, no indigenously acquired measles cases were reported in the United States (5). Twenty states and the District of Columbia reported no indigenous cases during the year (Table_2).

Rubella. In 1996, a provisional total of 196 confirmed indigenously acquired cases of rubella were reported; of these, nine (5%) occurred among children aged less than 5 years (Table_1). A total of 114 (58%) cases occurred among persons of Hispanic ethnicity; of these persons, 94 (82%) were aged greater than or equal to 20 years. In addition, several outbreaks occurred among foreign-born persons who were natives of countries without rubella vaccination programs (6). The number of cases of indigenously acquired rubella reported in 1996 represents a twofold decline from the median number of cases reported during 1988-1992 (Table_1). Twenty-eight states and the District of Columbia reported no indigenously acquired rubella in 1996 (Table_2).

Diphtheria. Although two cases of diphtheria were provisionally reported to the NNDSS in 1996, ** endemic transmission of toxigenic Corynebacterium diphtheriae was detected in a Northern Plains Indian community in 1996 (7). Therefore, at least one focus of indigenous transmission persists in the United States. Of the cases reported to NIP with onset in 1996, one occurred in a person aged 15 years and the other three, among persons aged greater than 20 years. The low number of reported cases (a median of four cases annually during 1988-1992) may reflect low incidence of disease or lack of recognition of this rare disease. Forty-seven states and the District of Columbia reported no cases of diphtheria during 1996 (Table_2).

Hib. During 1996, a total of 49 cases of Hib invasive disease and 116 cases of H. influenzae of unknown serotype among children aged less than 5 years were provisionally reported (as of July 23, 1997) to NNDSS, NBMBRS, or through active surveillance sites. In 1996, a total of 13 states and the District of Columbia reported no cases of invasive disease caused by H. influenzae type b or an unknown serotype among children aged less than 5 years. In five of these states, however, zero cases of invasive H. influenzae disease of any type in any age group were reported, suggesting reporting is incomplete. Hib disease was not consistently reported to NNDSS during 1988-1992 ***. However, data from the active laboratory-based surveillance system coordinated by CDC indicate a 99% decrease during 1989-1995 in the incidence of invasive Hib disease among children aged less than 5 years (8).

Mumps. In 1996, a provisional total of 725 indigenous cases of mumps were reported; 154 (21%) cases occurred among children aged less than 5 years, and 380 (52%) occurred among children aged 5-19 years. In contrast, during 1988-1992, a median of 453 and 3167 cases occurred among persons aged less than 5 years and 5-19 years, respectively. In 1996, a total of 315 (43%) indigenous mumps cases were classified as confirmed; 194 (27%), as probable; and 216 (30%), as unknown.

Reported by: Child Vaccine Preventable Diseases Br, Epidemiology and Surveillance Div, National Immunization Program, CDC.

Editorial Note

Editorial Note: The findings of this report document achievement in 1996 of two of the six disease-elimination goals established by the CII (tetanus among children aged less than 15 years and polio caused by wild poliovirus) and the disease-reduction goal for mumps. Factors contributing to attainment of these goals include achieving record-high vaccination coverage among preschool-aged children, increasing coverage with the second dose of measles-mumps-rubella vaccine (MMR) among school-aged children, and decreasing risk for importation of polio worldwide. Reported incidence of the other targeted vaccine-preventable diseases remained at or near the lowest ever recorded.

Despite these accomplishments in eliminating vaccine-preventable diseases, four of the six disease-elimination goals established by the CII were not achieved at the national level in 1996. The reasons for this varied among the diseases targeted for elimination. For example, the epidemiology of measles and rubella has changed from that which existed before initiation of the CII. Disease-control measures and vaccination programs targeted at preschool-aged children are necessary, but not sufficient, to eliminate transmission of these diseases. Reducing susceptibility among young adults and administration of second doses of MMR to susceptible school-aged children will be critical to assure sustained elimination of transmission. Furthermore, persons who are natives of countries without rubella vaccination programs should be considered susceptible to rubella and, therefore, should be vaccinated unless they have documentation of prior vaccination or serologic evidence of immunity. Frequent importations of measles and rubella will require improved control of these diseases in other countries to reduce the risks for exposure among the remaining susceptible persons in the United States. Some populations that object to vaccination for religious or philosophic reasons continue to remain susceptible, and outbreaks among these populations may occur unless the risk for exposure to disease is minimized by reducing the risk for importation and by maintaining high vaccination levels in general populations. Cases of invasive Hib disease continue to occur among children who are too young to be fully protected with current vaccines and schedules, children who are not vaccinated at the recommended ages, and children who are not fully protected by existing vaccines (8). Additional efforts must be directed toward characterizing potential reservoirs of infection that are not eliminated by current vaccines and strategies to develop more effective vaccination programs. In addition, the persistent circulation of diphtheria despite high levels of vaccination (7) underscores the need for improved understanding of the indigenous foci of transmission to refine control strategies.

Although CII did not establish a disease-reduction goal for pertussis, the persistent ocurrence of this disease has important public health implications. Despite increasing vaccine coverage among preschool-aged children, the number of reported cases of pertussis has continued to increase: during 1988-1992, a median of 4083 cases was reported; in 1996, a provisional total of 7796 cases was reported. Although vaccine effectiveness remains high among preschool-aged children (9), older school-aged children now account for an increasing proportion of cases. Because pertussis vaccine is not recommended for use in persons aged greater than or equal to 7 years, these cases cannot be prevented by current vaccines and vaccination strategies. Studies are under way to assess the effectiveness and potential impact of the use of acellular pertussis vaccines in older age groups.

As vaccination and other disease-control efforts reduce disease incidence, more accurate data are needed for monitoring further progress toward disease-elimination objectives. Surveillance indicators that will allow monitoring of diagnostic efforts are needed to ensure that the absence of reported cases reflects the true absence of disease rather than the absence of effort to detect disease. Adequate laboratory evaluation of suspected cases also is critical and should include increased completeness of serotyping of H. influenzae isolates from cases of invasive disease in children. Only 43% of reported mumps cases were confirmed; if laboratory confirmation had been sought for the remaining cases, many probably would have been ruled out as cases. Molecular typing methods can assist in characterizing the origins (indigenous or imported) of agents; these methods have been used to demonstrate the interruption of transmission of measles virus (4) and ongoing endemic circulation of toxigenic C. diphtheriae strains (7). Similar methods are now being applied to better define the origin of circulating rubella strains in the United States.

References

  1. CDC. Reported vaccine-preventable diseases -- United States, 1993, and the Childhood Immunization Initiative. MMWR 1994;43:57-60.

  2. CDC. Status report on the Childhood Immunization Initiative: national, state, and urban area vaccination coverage levels among children aged 19-35 months -- United States, 1996. MMWR 1997;46:657-64.

  3. Strebel PM, Sutter RW, Cochi SL, et al. Epidemiology of poliomyelitis in the United States one decade after the last reported case of indigenous wild virus-associated disease. Clin Infect Dis 1992;14:568-79.

  4. CDC. Measles elimination in the United States -- measles eradication: recommendations from a meeting cosponsored by the World Health Organization, the Pan American Health Organization, and CDC. MMWR 1997;46(no. RR-11):12-4.

  5. CDC. Measles -- United States, 1996, and the interruption of indigenous transmission. MMWR 1997;46:242-6.

  6. CDC. Rubella and congenital rubella syndrome -- United States, 1994-1997. MMWR 1997;46: 350-4.

  7. CDC. Toxigenic Corynebacterium diphtheriae -- Northern Plains Indian Community, August- October 1996. MMWR 1997;46:506-10.

  8. CDC. Progress toward elimination of Haemophilus influenzae type b disease among infants and children -- United States, 1987-1995. MMWR 1996;46:901-6.

  9. Guris D, Strebel PM, Tachdjian R, Bardenheier B, Wharton M, Hadler SC. Effectiveness of pertussis vaccination program using the screening method, United States, 1992-1994. J Infect Dis 1997 (in press).

* Progress toward CII's goal of increasing vaccination coverage among children aged 19-35 months is presented in another report in this issue of MMWR (2).

** Two additional cases with onset in 1996 were reported to NIP but have not been reported to NNDSS.

*** Invasive Hib disease became nationally notifiable in 1991.




Table_1
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TABLE 1. Number of cases of vaccine-preventable diseases targeted for elimination by the Childhood Immunization Initiative
-- United States, 1988 -- 1992 and 1996 *
================================================================================================================================
                                                                             No. 1996 Cases
                                                                     --------------------------------------
                                      No. reported cases                                         Cases in
                            -------------------------------------             Indigenously    children aged
Disease                      1988    1989    1990    1991    1992    Total    acquired cases     <5 years
-----------------------------------------------------------------------------------------------------------
Diphtheria                      2       3       4       5       4        4 +           4 *           0
Invasive Hib disease @         NN      NN      NN   1,540     592      230           230           230
Measles                     3,396  18,193  27,786   9,643   2,237      510 **        446           129
Poliomyelitis ++                0       0       0       0       0        0             0             0
Rubella                       225     396   1,125   1,401     160      233 **        196             9
Tetanus &&                      2       2       3       3       3        0             0             0
Mumps                       4,866   5,712   5,292   4,264   2,572      746           720           154
-----------------------------------------------------------------------------------------------------------
*  Data for 1996 are provisional as of June 23, 1997.
+  Including two cases reported to CDC but not reported as 1996 cases to the National Notifiable Diseases Surveillance System.
&  Among children aged <5 years; includes Haemophilus influenzae cases classified as type b or of unknown serotype.
@  Not nationally notifiable.
** Confirmed and unknown case status only.
++ Indigenously acquired cases caused by wild poliovirus.
&& Among children aged <15 years.
================================================================================================================================

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Table_2
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TABLE 2. Number of reported cases * of selected vaccine-preventable diseases, by
state, -- United States, 1996

                                                                                              Hi type b
                                                                                                 or
State                  Measles +     Rubella +     Polio &     Diphtheria @    Tetanus **     unknown ++
--------------------------------------------------------------------------------------------------------
Alabama                    0            2            0              0             0               2
Alaska                    63            0            0              0             0               5
Arizona                    8            3            0              0             0               3
Arkansas                   0            0            0              0             0               0
California                37           42            0              0             0              18
Colorado                   6            3            0              0             0               2
Connecticut                2            4            0              0             0               1
Delaware                   1            0            0              0             0               1
District of Columbia       0            0            0              0             0               0
Florida                    0           11            0              0             0              16
Georgia                    1            0            0              0             0              12
Hawaii                    40            1            0              0             0               0
Idaho                      1            2            0              0             0               0
Illinois                   2            1            0              0             0              12
Indiana                    0            0            0              1             0               3
Iowa                       0            0            0              0             0               2
Kansas                     0            0            0              0             0               1
Kentucky                   0            0            0              1             0               1
Louisiana                  1            1            0              0             0               1
Maine                      0            0            0              0             0               0
Maryland                   0            0            0              0             0               7
Massachusetts              9           17            0              0             0               3
Michigan                   0            0            0              0             0               5
Minnesota                 17            0            0              0             0               2
Mississippi                0            0            0              0             0               0
Missouri                   3            0            0              0             0               1
Montana                    0            0            0              0             0               0
Nebraska                   0            0            0              0             0               1
Nevada                     5            1            0              0             0               0
New Hampshire              0            0            0              0             0               3
New Jersey                 3            2            0              0             0               9
New Mexico                17            0            0              0             0               2
New York                   3            5            0              0             0               2
New York City              8            3            0              1             0               6
North Carolina             1           72            0              0             0               8
North Dakota               0            0            0              0             0               0
Ohio                       2            0            0              0             0               7
Oklahoma                   0            0            0              0             0               3
Oregon                    13            1            0              0             0               0
Pennsylvania              10            1            0              0             0               2
Rhode Island               1            0            0              0             0               1
South Carolina             0            1            0              0             0               0
South Dakota               0            0            0              1             0               0
Tennessee                  2            0            0              0             0               7
Texas                     24            5            0              0             0               3
Utah                     117            0            0              0             0               1
Vermont                    1            1            0              0             0               0
Virginia                   0            2            0              0             0               4
Washington                36           15            0              0             0               5
West Virginia              0            0            0              0             0               1
Wisconsin                  8            0            0              0             0               4
Wyoming                    1            0            0              0             0               0

Total                    446          196            0              4             0             230
--------------------------------------------------------------------------------------------------------
*  Includes cases reported to the National Notifiable Diseases Surveillance System (NNDSS) as
   indigenous or of unknown case status. Data are provisional as of July 23, 1997.
+  Cofirmed and unknown case status only.
&  Caused by wild virus.
@  Includes two probable or confirmed cases reported to the National Immunization Program
   but not reported as 1996 cases to NNDSS. Cases reported to NNDSS are supplemented by
   data from other surveillance systems.
** Among children aged <15 years.
++ Data are not collected for indigenous versus imported cases. Total includes invasive
   disease caused by Haemophilus influenzae type b or an unknown serotype among children
   aged <5 years. Cases reported to NNDSS with onset dates in 1996 are supplemented by
   data from other surveillance systems (e.g., the National Bacterial Meningitis and Bacteremia
   Reporting Surveillance System and laboratory-based active surveillance, both conducted by CDC's
   Childhood and Respiratory Diseases Branch, Division of Bacterial and Mycotic Diseases,
   National Center for Infectious Diseases).
&& No cases of Haemophilus influenzae disease (of any serotype or of unknown serotype)
   among any age group reported to NNDSS.
===========================================================================================================

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