A baby under one with severe or repeated infections, failure to gain weight, and persistent thrush needs urgent immune testing. Severe combined immunodeficiency is a paediatric emergency. Live vaccines, including BCG and oral polio, can be fatal in these babies.
A child born with a defective immune system. Infections that other children shrug off become severe, repeated and sometimes fatal — and for the most serious forms, transplant is the only cure.
These conditions are individually rare but collectively important, and they are considerably more common where marriage between relatives is customary. The severe forms are emergencies, and the delay before diagnosis is what costs children their lives.
More than four hundred inherited conditions affect the immune system, and they range from mild antibody deficiencies causing recurrent chest infections to a complete absence of functioning immune cells.
Severe combined immunodeficiency is the most urgent. Affected babies have essentially no functioning T cells, appear well for the first weeks while protected by their mother's antibodies, and then develop persistent thrush, chronic diarrhoea, severe chest infections and failure to gain weight. Untreated, it is almost always fatal in the first two years. Transplant performed in the first few months of life, before serious infection has taken hold, gives markedly better results than transplant later.
Other important groups include antibody deficiencies, which present with repeated chest and sinus infections; phagocyte defects such as chronic granulomatous disease, which cause deep abscesses and unusual infections; and immune dysregulation syndromes, in which the immune system attacks the body's own tissues.
A critical practical point: live vaccines are dangerous in these children. BCG, given routinely at birth across most of our markets, can cause disseminated infection in a baby with SCID. Where a family has already lost an infant to unexplained infection, the next baby's vaccination should be discussed with an immunologist before it is given.
BCG, oral polio and rotavirus are live vaccines, and in a baby with severe combined immunodeficiency they can cause disseminated, life-threatening infection. BCG is given at birth in most of our markets, frequently before any immune problem is suspected. If a previous child in the family died of infection in infancy, or the parents are related and a sibling has been affected, the next baby's immune function should be assessed before vaccination — and the newborn should be discussed with an immunologist urgently rather than at a routine visit.
Simple blood tests screen; specialist testing confirms and identifies the exact defect.
If a full blood count has ever been done, send it — a persistently low absolute lymphocyte count in an infant is a strong indicator of severe combined immunodeficiency and is frequently reported without comment. Send it alongside immunoglobulin levels, any flow cytometry, the details of every serious infection, and whether the parents are related or any previous child died in infancy. That family history is genuinely diagnostic information.
Supportive treatment protects the child; transplant is what cures the severe forms.
Prophylactic antibiotics and antifungals, immunoglobulin replacement where antibody production is deficient, strict avoidance of live vaccines, and irradiated blood products only. For a baby with suspected SCID, isolation and urgent referral. These measures keep the child alive while definitive treatment is arranged.
Replacing the defective immune system with donor stem cells cures severe combined immunodeficiency and several other severe forms. Results are markedly better when performed early, before serious infection has become established, and in a baby under three to four months the outcomes are excellent. A matched sibling gives the best results; a half-matched parent is used where none exists.
For antibody deficiencies, regular infusions of immunoglobulin replace the antibodies the child cannot make. Given intravenously every few weeks or subcutaneously at home weekly, it substantially reduces infections. It is a lifelong treatment rather than a cure, and it is available in your own country.
For certain specific defects, correcting the gene in the child's own stem cells avoids the need for a donor and the risk of graft-versus-host disease. It is available for a small number of conditions at a small number of centres worldwide, and it is not currently a routine option for most families.
Genetic diagnosis determines whether transplant is curative, whether immunoglobulin suffices, and what conditioning is safe.
SCID in an infant is an emergency where every week matters. Antibody deficiency in an older child allows time to plan properly.
HLA type all siblings immediately where transplant is likely. A half-matched parent is available to almost every child.
If your baby is under a year with persistent thrush, diarrhoea and failure to thrive, ask for lymphocyte subsets urgently. That single test can change everything.
A baby with suspected severe combined immunodeficiency needs urgent specialist care and protection from infection where you are. Transplant is arranged as fast as possible afterwards.
Photographs taken on your phone are fine. Reports in Arabic, Russian or Bengali are fine — we translate them ourselves.
Repeated severe infections needing intravenous antibiotics, two or more pneumonias in a year, persistent thrush beyond infancy, chronic diarrhoea with failure to gain weight, deep abscesses, and infections with unusual organisms. A family history of infant deaths from infection, or parents who are related, raises the suspicion considerably.
Live vaccines contain weakened but living organisms that a normal immune system controls easily. A child with severe combined immunodeficiency cannot, and the vaccine organism can spread and cause fatal infection. BCG is given at birth across most of our markets, often before any problem is suspected — which is why family history matters so much.
For severe combined immunodeficiency and several other severe forms, yes — replacing the immune system with donor stem cells is curative. Results are considerably better when performed early, and in a baby transplanted in the first few months before serious infection has taken hold, outcomes are excellent.
It is relevant medical information rather than a judgement. Marriage between relatives increases the chance that both parents carry the same recessive gene, and most severe immunodeficiencies are recessive. Knowing it helps doctors reach the diagnosis faster and informs testing of other children and genetic counselling for future pregnancies.
Tell the obstetric and paediatric team before delivery, and arrange for the newborn's immune function to be assessed before any live vaccine is given. Where the genetic defect in the first child was identified, the new baby can be tested specifically and rapidly. This is one of the situations where planning ahead genuinely saves a life.
Yes, in most countries, and subcutaneous immunoglobulin can be given at home weekly by the family after training. For antibody deficiency syndromes this is the mainstay of treatment and does not require travelling. What is worth travelling for is establishing the precise diagnosis and, where transplant is indicated, the transplant itself.
Send the full blood count with the absolute lymphocyte count, immunoglobulin levels and any flow cytometry. Tell us whether the parents are related and whether any previous child died in infancy.
Your reports go directly to our medical team. We do not share your records with hospitals until you tell us to.
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