Implementation of Universal Newborn Screening for Severe Combined Immunodeficiency in Singapore While Continuing Routine Bacille-Calmette-Guerin Vaccination Given at Birth

Abstract

IntroductionSevere Combined Immunodeficiency (SCID) is generally fatal if untreated; it predisposes to severe infections, including disseminated Bacille-Calmette-Guerin (BCG) disease from BCG vaccination at birth. However, delaying BCG vaccination can be detrimental to the population in tuberculosis-endemic regions. Early diagnosis of SCID through newborn screening followed by pre-emptive treatment with anti-mycobacterial therapy may be an alternative strategy to delaying routine BCG vaccination. We report the results of the first year of newborn SCID screening in Singapore while continuing routine BCG vaccination at birth.MethodNewborn screening using a T-cell receptor excision circle (TREC) assay was performed in dried blood spots received between 10 October 2019 to 9 October 2020 using the Enlite Neonatal TREC kit. Patients with low TREC had lymphocyte subset analysis and full blood count performed to determine the severity of lymphopenia and likelihood of SCID to guide further management.ResultsOf the 35888 newborns screened in 1 year, no SCID cases were detected, while 13 cases of non-SCID T-cell lymphopenia (TCL) were picked up. Using a threshold for normal TREC to be >18 copies/μL, the retest rate was 0.1% and referral rate to immunologist was 0.04%. Initial low TREC correlated with low absolute lymphocyte counts (ALC), and subsequent normal ALC corresponded with increases in TREC, thus patients with normal first CD3+ T cell counts were considered to have transient idiopathic TCL instead of false positive results. 7/13 (54%) had secondary TCL (from sepsis, Trisomy 21 with hydrops and stoma losses or chylothorax, extreme prematurity, or partial DiGeorge Syndrome) and 6/13 (46%) had idiopathic TCL. No cases of SCID were diagnosed clinically in Singapore during this period and for 10 months after, indicating that no cases were missed by the screening program. 8/9 (89%) of term infants with abnormal TREC results received BCG vaccination within the first 6 days of life when TREC and ALC were low. No patients developed BCG complications after a median follow-up of 17 months.ConclusionNewborn screening for SCID can be implemented while continuing routine BCG vaccination at birth. Patients with transient TCL and no underlying primary immunodeficiency are able to tolerate BCG vaccination.

Primary immunodeficiencies (PID) Life Index in Southeast Asia: A comparative analysis of PID Principles of Care (PoC)

“…The only other SEA country which had started on SCID newborn screening program is Singapore, however it is not included in our analysis as Singapore is not part of the contributing countries for PID Life Index. Nonetheless, through the Singapore’s experience, within a span of one year, the newborn screening program (NBS) had successfully identified 13 cases of non-SCID T-cell lymphopenia using T-cell receptor excision circle (TREC) assay performed in dried blood spots of 35888 newborns ( 15 ).…”

Current Status of Newborn Bloodspot Screening Worldwide 2024: A Comprehensive Review of Recent Activities (2020–2023)

“…Along with the NBS for SCID came questions about its implementation in settings where BCG (bacille Calmette-Guerin) vaccination was given to newborns. The results of implementing SCID NBS in Singapore were published in 2022 and showed that patients with transient non-SCID T-cell lymphopenia and no underlying primary immunodeficiency can tolerate the BCG vaccination [ 638 ].…”

Paving the way in implementation of SCID newborn screening in developing nations: feasibility study and strategies to move forward in Malaysia

“…An increasing number of countries worldwide have adopted this newborn screening program, including Canada, Iceland, Ireland, Switzerland, Germany, Czech Republic, Netherlands, Denmark, Finland, Sweden, Norway, Ukraine, Israel, Qatar, New Zealand, Hong Kong, Taiwan and Singapore (1,(19)(20)(21)(22). Additionally, some other countries have also embarked on initiatives towards SCID newborn screening program, which includes either regional implementation or a pilot project, in the United Kingdom, Italy, France, Argentina, Belgium, Spain, Slovenia, Slovakia, Bulgaria, Turkey, Poland, Belarus, Brazil, Kazakhstan, Russia, Australia, Japan, South Korea, China, Austria, Saudi Arabia, Iran, and Lebanon (19, [23][24][25][26][27][28].…”