SCID (Severe Combined Immunodeficiency) in Babies
Medically reviewed by Dr. Michael Okonkwo, MD, FAAP · Board-Certified Neonatologist
Content reviewed against published AAP, NIH, IDF guidelines
Last reviewed:
If your baby has been diagnosed with or you suspect scid (severe combined immunodeficiency) in babies, here is what the evidence says.
The short answer
Severe combined immunodeficiency (SCID) is a group of rare, life-threatening genetic disorders in which a baby is born with virtually no functioning immune system. Babies with SCID lack T-cells and sometimes B-cells and NK-cells, leaving them unable to fight infections. SCID is now detected through newborn screening in all U.S. states. Without treatment, most babies with SCID do not survive past their first year. However, bone marrow (hematopoietic stem cell) transplant performed early — ideally before 3.5 months and before infections develop — is curative in over 90% of cases.
Key takeaways
- Severe combined immunodeficiency (SCID) is a group of rare, life-threatening genetic disorders in which a baby is born with virtually no functioning immune system. Babies with SCID lack T-cells and sometimes B-cells and NK-cells, leaving them unable to fight infections. SCID is now detected through newborn screening in all U.S. states. Without treatment, most babies with SCID do not survive past their first year. However, bone marrow (hematopoietic stem cell) transplant performed early — ideally before 3.5 months and before infections develop — is curative in over 90% of cases.
- Usually normal when: Your baby's newborn screening was normal and they are growing and developing well
- Call your doctor if: Your baby has a positive newborn screen for SCID — this requires urgent immunology evaluation, even though your baby may look perfectly healthy right now
- Varies by age — see the age-by-age breakdown below
“Fever itself is not an illness — rather, it is a sign or symptom that the body is fighting an infection. Fever stimulates certain defenses, such as the white blood cells, which attack and destroy invading bacteria.”
This is one of the most common questions parents ask. Searching for answers means you care.
What Parents Should Know
According to AAP, NIH, IDF guidelines, severe combined immunodeficiency (SCID) is a group of rare, life-threatening genetic disorders in which a baby is born with virtually no functioning immune system. Babies with SCID lack T-cells and sometimes B-cells and NK-cells, leaving them unable to fight infections. SCID is now detected through newborn screening in all U.S. states. Without treatment, most babies with SCID do not survive past their first year. However, bone marrow (hematopoietic stem cell) transplant performed early — ideally before 3.5 months and before infections develop — is curative in over 90% of cases. At 0-3 months, sCID is typically identified through newborn screening, which detects low T-cell receptor excision circles (TRECs). A positive screen requires urgent follow-up with a pediatric immunologist for confirmatory testing (lymphocyte subsets, mitogen proliferation studies). Babies appear healthy at birth because they are still protected by maternal antibodies. It is critical to avoid live vaccines (especially rotavirus and BCG) and to minimize infection exposure. Early referral for bone marrow transplant evaluation is essential — transplant before 3.5 months of age and before infections occur yields the best survival rates (over 95%). It is generally considered normal when your baby's newborn screening was normal and they are growing and developing well. However, you should contact your pediatrician promptly if your baby has a positive newborn screen for SCID — this requires urgent immunology evaluation, even though your baby may look perfectly healthy right now.
Normal vs. Concerning
When to Seek Immediate Care
- Your baby has a positive newborn screen for SCID — this requires urgent immunology evaluation, even though your baby may look perfectly healthy right now
- Your baby has severe pneumonia, sepsis, or an infection that is not responding to treatment, especially if combined with failure to thrive or chronic diarrhea
- Your baby with known SCID develops any fever or signs of infection — even minor infections can be life-threatening and require immediate emergency care
By Age
What to expect by age
0-3 months
SCID is typically identified through newborn screening, which detects low T-cell receptor excision circles (TRECs). A positive screen requires urgent follow-up with a pediatric immunologist for confirmatory testing (lymphocyte subsets, mitogen proliferation studies). Babies appear healthy at birth because they are still protected by maternal antibodies. It is critical to avoid live vaccines (especially rotavirus and BCG) and to minimize infection exposure. Early referral for bone marrow transplant evaluation is essential — transplant before 3.5 months of age and before infections occur yields the best survival rates (over 95%).
3-6 months
If SCID was not caught on newborn screening, symptoms may begin appearing as maternal antibodies wane. Warning signs include persistent thrush that does not respond to treatment, chronic diarrhea, failure to thrive, recurrent pneumonia, and skin rashes (often from graft-versus-host disease caused by maternal T-cells). Infections with organisms that rarely cause disease in healthy babies — such as Pneumocystis jirovecii pneumonia — are a hallmark of SCID. Immediate immunology evaluation is needed.
6-12 months
Babies with undiagnosed SCID at this age typically develop severe, recurrent, and life-threatening infections including pneumonia, meningitis, sepsis, and chronic viral infections. Growth faltering becomes pronounced. Without treatment, the prognosis is poor. Even at this stage, bone marrow transplant can be life-saving, though outcomes are better when transplant occurs before serious infections develop. Gene therapy is also emerging as a treatment option for certain SCID types (ADA-SCID, X-linked SCID).
1-3 years
Children who have undergone successful bone marrow transplant for SCID are typically developing well and building functional immune systems. They require close follow-up with immunology to monitor immune reconstitution, may need booster vaccinations once the immune system recovers, and some may require ongoing immunoglobulin replacement. For ADA-SCID, enzyme replacement therapy (PEG-ADA) can serve as a bridge to definitive treatment. Long-term outcomes with early treatment are excellent.
What to Tell Your Pediatrician
- Describe when you first noticed scid (severe combined immunodeficiency) in babies and how it has changed over time.
- Note your baby's current age and which age-specific patterns you are seeing.
- Mention if your baby's newborn screening flagged for possible SCID — follow up with immunology as directed.
- Mention if your baby has persistent thrush, chronic diarrhea, or recurrent respiratory infections that seem more severe than expected.
- Let your doctor know if you have noticed any related concerns, such as changes in feeding, sleep, or movement patterns.
- Bring a list of any questions or observations you want to discuss at the appointment.
What Should You Do?
When to take action
- Your baby's newborn screening was normal and they are growing and developing well
- Your baby gets typical colds and recovers within the expected timeframe
- Your baby had a false-positive SCID screen that was cleared by confirmatory testing — false positives can occur in premature infants
- Your baby who was treated for SCID is meeting milestones and immune function tests are improving
- Your baby's newborn screening flagged for possible SCID — follow up with immunology as directed
- Your baby has persistent thrush, chronic diarrhea, or recurrent respiratory infections that seem more severe than expected
- You have a family history of SCID, infant deaths from infection, or known immunodeficiency
- Your baby has a positive newborn screen for SCID — this requires urgent immunology evaluation, even though your baby may look perfectly healthy right now
- Your baby has severe pneumonia, sepsis, or an infection that is not responding to treatment, especially if combined with failure to thrive or chronic diarrhea
- Your baby with known SCID develops any fever or signs of infection — even minor infections can be life-threatening and require immediate emergency care
What You Can Do at Home
- Keep track of when you notice scid (severe combined immunodeficiency) in babies — noting the time of day, duration, and any triggers can help your pediatrician.
- Remember that your baby's newborn screening was normal and they are growing and developing well — this is generally within the range of normal.
- At 0-3 months, focus on observation rather than intervention unless your pediatrician advises otherwise.
- Follow any care instructions from your pediatrician. Keep a written log of symptoms to bring to appointments.
- While monitoring at home, seek immediate care if your baby has a positive newborn screen for SCID — this requires urgent immunology evaluation, even though your baby may look perfectly healthy right now.
Related Conditions
Signs of Primary Immunodeficiency in Babies
Primary immunodeficiency disorders are conditions where the immune system does not function properly from birth. Warning signs include 4 or more new ear infections in a year, 2 or more serious sinus infections in a year, 2 or more months on antibiotics with little effect, 2 or more pneumonias in a year, failure to thrive, recurrent deep skin or organ abscesses, and a family history of primary immunodeficiency. These conditions are rare but treatable when identified early.
Warning Signs of Primary Immunodeficiency in Children
Primary immunodeficiency diseases (PIDs) are a group of over 450 genetic conditions where the immune system does not function properly. The Jeffrey Modell Foundation has identified 10 warning signs in children: 4+ new ear infections in a year, 2+ serious sinus infections in a year, 2+ months on antibiotics with little effect, 2+ pneumonias in a year, failure to gain weight or grow normally, recurrent deep skin or organ abscesses, persistent thrush in mouth or fungal infection on skin, need for IV antibiotics to clear infections, 2+ deep-seated infections (sepsis, meningitis), and a family history of PID. If your child meets 2 or more of these criteria, discuss immunologic testing with your pediatrician.
How Often Do Babies Get Sick? What's Normal
It is normal for babies and toddlers to get 6-8 upper respiratory infections (colds) per year, and children in daycare may have even more — up to 8-12 illnesses annually. According to the AAP, the average child will have experienced 80-100 viral infections by their 6th birthday. Babies in group childcare settings tend to get sick more frequently in their first 1-2 years (often called the "germ year") but research shows they have fewer infections in later childhood compared to children who were not in early group care, as their immune systems were exposed sooner. Each cold typically lasts 7-10 days, and with back-to-back infections, it can feel like your baby is sick continuously through the fall and winter months. This frequent illness, while exhausting for families, is a normal part of immune system development.
Related Resources
Frequently asked questions
Is scid (severe combined immunodeficiency) in babies normal?
When should I call the doctor about scid (severe combined immunodeficiency) in babies?
When is scid (severe combined immunodeficiency) in babies normal?
What causes scid (severe combined immunodeficiency) in babies?
What should I mention to my pediatrician about scid (severe combined immunodeficiency) in babies?
Is scid (severe combined immunodeficiency) in babies normal at 0-3 months?
Is scid (severe combined immunodeficiency) in babies normal at 3-6 months?
Should I go to the ER for scid (severe combined immunodeficiency) in babies?
Does scid (severe combined immunodeficiency) in babies go away on its own?
References
- [1]American Academy of Pediatrics. Newborn Screening for Severe Combined Immunodeficiency. Pediatrics, 2018. AAP
- [2]National Institute of Allergy and Infectious Diseases. Severe Combined Immunodeficiency (SCID). NIAID, 2023. NIH
- [3]Immune Deficiency Foundation. SCID - Severe Combined Immune Deficiency. IDF, 2024. IDF
Doctor Visit Checklist
Bring this checklist to your next pediatrician visit to discuss SCID (Severe Combined Immunodeficiency) in Babies.
Things to mention
- Describe when you first noticed scid (severe combined immunodeficiency) in babies and how it has changed over time.
- Note your baby's current age and which age-specific patterns you are seeing.
- Mention if your baby's newborn screening flagged for possible SCID — follow up with immunology as directed.
- Mention if your baby has persistent thrush, chronic diarrhea, or recurrent respiratory infections that seem more severe than expected.
- Let your doctor know if you have noticed any related concerns, such as changes in feeding, sleep, or movement patterns.
- Bring a list of any questions or observations you want to discuss at the appointment.
Observations to share
- Your baby's newborn screening flagged for possible SCID — follow up with immunology as directed
- Your baby has persistent thrush, chronic diarrhea, or recurrent respiratory infections that seem more severe than expected
- You have a family history of SCID, infant deaths from infection, or known immunodeficiency
Urgent signs to report immediately
- Your baby has a positive newborn screen for SCID — this requires urgent immunology evaluation, even though your baby may look perfectly healthy right now
- Your baby has severe pneumonia, sepsis, or an infection that is not responding to treatment, especially if combined with failure to thrive or chronic diarrhea
- Your baby with known SCID develops any fever or signs of infection — even minor infections can be life-threatening and require immediate emergency care
My notes
From ismybabyalright.com — free, evidence-based baby health guides
All content follows our editorial policy and is reviewed against published clinical guidelines.
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Related Resources
Bottom line
Most cases of scid (severe combined immunodeficiency) in babies are normal. Talk to your pediatrician if your baby has a positive newborn screen for scid — this requires urgent immunology evaluation, even though your baby may look perfectly healthy right now.
Trust your instincts. If something feels wrong, reach out to your pediatrician. Worrying about your baby means you care — that is a good thing.
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Related Medical Concerns
Signs of Primary Immunodeficiency in Babies
Primary immunodeficiency disorders are conditions where the immune system does not function properly from birth. Warning signs include 4 or more new ear infections in a year, 2 or more serious sinus infections in a year, 2 or more months on antibiotics with little effect, 2 or more pneumonias in a year, failure to thrive, recurrent deep skin or organ abscesses, and a family history of primary immunodeficiency. These conditions are rare but treatable when identified early.
Warning Signs of Primary Immunodeficiency in Children
Primary immunodeficiency diseases (PIDs) are a group of over 450 genetic conditions where the immune system does not function properly. The Jeffrey Modell Foundation has identified 10 warning signs in children: 4+ new ear infections in a year, 2+ serious sinus infections in a year, 2+ months on antibiotics with little effect, 2+ pneumonias in a year, failure to gain weight or grow normally, recurrent deep skin or organ abscesses, persistent thrush in mouth or fungal infection on skin, need for IV antibiotics to clear infections, 2+ deep-seated infections (sepsis, meningitis), and a family history of PID. If your child meets 2 or more of these criteria, discuss immunologic testing with your pediatrician.
How Often Do Babies Get Sick? What's Normal
It is normal for babies and toddlers to get 6-8 upper respiratory infections (colds) per year, and children in daycare may have even more — up to 8-12 illnesses annually. According to the AAP, the average child will have experienced 80-100 viral infections by their 6th birthday. Babies in group childcare settings tend to get sick more frequently in their first 1-2 years (often called the "germ year") but research shows they have fewer infections in later childhood compared to children who were not in early group care, as their immune systems were exposed sooner. Each cold typically lasts 7-10 days, and with back-to-back infections, it can feel like your baby is sick continuously through the fall and winter months. This frequent illness, while exhausting for families, is a normal part of immune system development.
My Baby's Head Shape Looks Abnormal
Many babies develop temporary head shape irregularities that are completely normal. A cone-shaped head from vaginal delivery reshapes within days. Mild positional flattening (plagiocephaly) from sleeping on the back is very common and usually improves with repositioning and tummy time. However, head shape changes involving ridges, a persistently bulging fontanelle, or rapid head growth changes should be evaluated to rule out craniosynostosis.
Achondroplasia (Dwarfism) in Babies
Achondroplasia is the most common form of short-limbed dwarfism, affecting about 1 in 15,000 to 40,000 births. It is caused by a mutation in the FGFR3 gene and is usually apparent at birth with characteristic features including short limbs, a larger head, and a prominent forehead. Intelligence is normal. With monitoring for specific complications and supportive care, children with achondroplasia lead full, active, and independent lives.
Adenoid Hypertrophy and Breathing
Adenoids are lymphoid tissue located behind the nose that help fight infection in young children. When adenoids become enlarged (adenoid hypertrophy), they can block the nasal airway, causing chronic mouth breathing, snoring, nasal speech, and sleep-disordered breathing. Enlarged adenoids are most common between ages 2-7 and are a leading cause of obstructive sleep apnea in young children. Treatment ranges from watchful waiting and nasal steroids to surgical removal (adenoidectomy) if breathing or sleep is significantly affected.