We retrieved data on DTP, OPV, and Haemophilus influenzae type b (Hib) immunisation coverage using existing surveys [9 (link),15 ,20 ,21 (link)]. DTP, OPV, and the Hib vaccine are all scheduled during the first 6 months of life (at 2, 4, and 6 months), which is the peak age range for SIDS [22 (link)]. To ensure comparability over time, we used the reported coverage of at least three doses of the respective vaccine. From 1995 onwards, any pertussis vaccine was reported including acellular pertussis vaccine (DTaP) [16 ].
The following three surveys provided data on immunisation coverage in the United States: the United States Immunization Survey (USIS; 1968–1985), the National Health Interview Survey (NHIS; 1991–1993), and the National Immunization Survey (NIS; 1994–2009) [9 (link),15 ,20 ,21 (link)]. The USIS started as an area-probability household survey using face-to-face interviews and became a telephone survey in 1971 [9 (link)]. Until 1978, the USIS assessed the immunisation of children between 1 and 4 years of age. Between 1979 and 1985, the survey included only children aged 24–35 months. The collected information was based on either parental recall or an immunisation record that was maintained at home. There was a lack of information on immunisation coverage from 1986–1990. From 1991 onwards, the NHIS assessed the immunisation status of children aged 19–35 months [20 ,23 ,24 ]. The NHIS examined a representative probability sample of households in the United States using face-to-face interviews. If a child’s immunisation records were available, the data were abstracted from the records; otherwise, the collected information was based on parental recall. Then, in 1994, the CDC implemented the NIS for continuous monitoring of immunisation coverage [15 ,21 (link)]. For 1994, we used the Morbidity and Mortality Weekly Report, and for the years 1995–2009, we used the public use files that are published on the CDC website [15 ,16 ]. The NIS is a random-digit-dialling telephone survey of households with children aged 19–35 months. The data were validated with the immunisation history of the child, which was obtained from the family’s health care provider [25 ]. The NIS and NHIS yielded similar results for estimated immunisation coverage levels [15 ]. In the current study, immunisation coverage is presented graphically as the percentage of children who were immunised with DTP, OPV, and the Hib vaccine in each year during the time period from 1968 to 2009.
The following three surveys provided data on immunisation coverage in the United States: the United States Immunization Survey (USIS; 1968–1985), the National Health Interview Survey (NHIS; 1991–1993), and the National Immunization Survey (NIS; 1994–2009) [9 (link),15 ,20 ,21 (link)]. The USIS started as an area-probability household survey using face-to-face interviews and became a telephone survey in 1971 [9 (link)]. Until 1978, the USIS assessed the immunisation of children between 1 and 4 years of age. Between 1979 and 1985, the survey included only children aged 24–35 months. The collected information was based on either parental recall or an immunisation record that was maintained at home. There was a lack of information on immunisation coverage from 1986–1990. From 1991 onwards, the NHIS assessed the immunisation status of children aged 19–35 months [20 ,23 ,24 ]. The NHIS examined a representative probability sample of households in the United States using face-to-face interviews. If a child’s immunisation records were available, the data were abstracted from the records; otherwise, the collected information was based on parental recall. Then, in 1994, the CDC implemented the NIS for continuous monitoring of immunisation coverage [15 ,21 (link)]. For 1994, we used the Morbidity and Mortality Weekly Report, and for the years 1995–2009, we used the public use files that are published on the CDC website [15 ,16 ]. The NIS is a random-digit-dialling telephone survey of households with children aged 19–35 months. The data were validated with the immunisation history of the child, which was obtained from the family’s health care provider [25 ]. The NIS and NHIS yielded similar results for estimated immunisation coverage levels [15 ]. In the current study, immunisation coverage is presented graphically as the percentage of children who were immunised with DTP, OPV, and the Hib vaccine in each year during the time period from 1968 to 2009.
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