In patients with higher risk for SCID and who would qualify for vaccination with BCG, there are rare but significant risks of disseminated BCG disease.139,153,154,155–161 As of 2021, newborn screening for SCID has been implemented in Alberta, Ontario, Manitoba, Prince Edward Island, Nova Scotia, New Brunswick and the Northwest Territories, with the rest of the provinces and territories in the process of implementation or evaluation (Dr. P. Chakraborty personal communication). The assay for T-cell receptor excision circle (TREC) identifies infants with most forms of SCID. Some programs have added other tests that target specific types of SCID. The positive predictive value of the screen is 37.5% (Newborn Screening Ontario 2020 annual report). In the absence of national guidelines, some jurisdictions (Nunavut and Northern Manitoba) have implemented delayed administration of BCG until the results of the SCID Newborn Screen are available, to prevent potential disseminated BCG disease. Programmatic evaluation is needed to ensure that this policy change has not diminished BCG vaccine uptake among those who would qualify. In populations receiving BCG vaccination at birth, without prior SCID newborn screening, one must have a high index of suspicion for disseminated BCG disease.
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