The immune system protects the child in layers:
- Innate (nonspecific) immunity — acts first and immediately: skin and mucous membranes, secretions, complement proteins, neutrophils and macrophages (phagocytosis), and natural killer cells
- Adaptive (specific) immunity — slower but targeted and with memory: B cells make antibodies (humoral immunity); T cells kill infected cells and direct the response (cell-mediated immunity)
The developing immune system
- Maternal IgG crosses the placenta and protects the infant for the first months (passive immunity) — preterm infants receive less
- Breast milk supplies secretory IgA and other protective factors
- The newborn's own antibody production, complement activity, and neutrophil function are immature; IgG falls to its lowest level at about 3–6 months (transient hypogammaglobulinemia of infancy), then rises
Immune problems in children fall into four groups: immunodeficiency (too little), hypersensitivity (an exaggerated response), autoimmunity (response against self), and vasculitis (immune-mediated vessel inflammation).
Primary immunodeficiencies (examples)
| Disorder | Defect | Features |
|---|
| Severe combined immunodeficiency (SCID) | Absent T-cell function (B-cell function also impaired) | Severe, recurrent infections from the first months, chronic diarrhea, failure to thrive, thrush, Pneumocystis pneumonia; fatal without stem cell transplant. Detected by newborn screening (TREC assay) in many places |
| X-linked agammaglobulinemia (Bruton) | No B cells → almost no antibodies (boys) | Recurrent bacterial infections (ears, sinuses, lungs) after maternal antibodies wane at 6 months |
| Wiskott–Aldrich syndrome | X-linked | Triad: recurrent infections, thrombocytopenia with small platelets (bleeding), eczema |
| DiGeorge syndrome (22q11.2 deletion) | Absent or small thymus → T-cell deficiency | Conotruncal heart defects, hypocalcemia (absent parathyroids), facial features, cleft palate |
| Selective IgA deficiency | Low IgA (most common immunodeficiency) | Often no symptoms; sinopulmonary and GI infections, celiac disease; risk of anaphylaxis to blood products containing IgA |
| Chronic granulomatous disease | Phagocytes cannot kill certain bacteria and fungi | Abscesses, pneumonia, granulomas |
| Complement deficiency (late components C5–C9) | Cannot form the membrane attack complex | Recurrent Neisseria (meningococcal) infections |
Secondary immunodeficiency — much more common: chemotherapy, long-term corticosteroids (e.g., nephrotic syndrome, lupus), transplant immunosuppression, malnutrition, asplenia, and HIV.
Hypersensitivity reactions
| Type | Mechanism | Examples |
|---|
| I — immediate (IgE) | Mast cell degranulation within minutes | Anaphylaxis, food allergy, allergic asthma, urticaria, allergic rhinitis |
| II — cytotoxic | Antibody against cell surface | Hemolytic transfusion reaction, hemolytic disease of the newborn |
| III — immune complex | Complexes deposit in vessels and tissues | Serum sickness, post-streptococcal glomerulonephritis, lupus, Arthus reaction (a local reaction at an injection site after repeated doses) |
| IV — delayed (T-cell) | Develops over 24–72 hours | Tuberculin skin test reaction, contact dermatitis (poison ivy, nickel) |
Autoimmune and vasculitic conditions
- Systemic lupus erythematosus (SLE) — multisystem autoimmunity; in children more often severe, with kidney (lupus nephritis) involvement
- Juvenile idiopathic arthritis (JIA) — arthritis for 6 weeks or more before age 16; risk of silent uveitis
- IgA vasculitis (Henoch–Schönlein purpura) — most common childhood vasculitis, often after a respiratory infection; palpable purpura on the legs and buttocks, arthritis, abdominal pain, and kidney involvement (nephritis)
- Autoimmune polyendocrine syndromes — type 1 diabetes with autoimmune thyroid disease and others (screen children with type 1 diabetes for thyroid disease and celiac disease)
Warning signs of primary immunodeficiency — several ear or sinus infections a year, two or more pneumonias in a year, infections needing IV antibiotics, recurrent deep abscesses, persistent thrush after age 1, failure to thrive, unusual organisms (Pneumocystis, severe fungal infections), and family history of immunodeficiency.
| Condition | Key findings |
|---|
| Anaphylaxis | Sudden onset minutes to hours after exposure: hives, flushing, lip or tongue swelling, stridor, wheeze, cough, hoarseness, vomiting, abdominal pain, hypotension, pallor, limpness; infants may only become sleepy or floppy |
| Food allergy | Hives, vomiting, eczema flare; peanuts, tree nuts, milk, egg, wheat, soy, fish, shellfish, sesame |
| SLE | Fever, fatigue, malar (butterfly) rash, photosensitivity, oral ulcers, arthritis, edema and hypertension (nephritis), cytopenias |
| JIA | Morning stiffness, joint swelling, limping, reduced activity; systemic JIA: daily spiking fever, salmon-pink rash |
| IgA vasculitis | Palpable purpura (legs, buttocks), joint pain, colicky abdominal pain (risk of intussusception), hematuria, proteinuria, hypertension |
| SCID | Infections from early infancy, chronic diarrhea, poor growth, absent tonsils and lymph nodes |
| Test | Use |
|---|
| CBC with differential, absolute lymphocyte count | Low lymphocytes in infants suggest SCID |
| Immunoglobulin levels (IgG, IgA, IgM, IgE); vaccine antibody responses | Antibody deficiencies |
| Lymphocyte subsets (flow cytometry) | T, B, and NK cells |
| Complement studies (CH50) | Complement deficiency — test after meningococcal infection |
| Newborn screening (TREC) | SCID |
| Serum tryptase | Supports anaphylaxis — never delays epinephrine |
| Skin prick tests, specific IgE, oral food challenge (supervised) | Food allergy |
| ANA, anti-dsDNA, complement C3/C4, urinalysis | SLE |
| Slit-lamp eye examination | Regular uveitis screening in JIA |
| Urinalysis and BP | IgA vasculitis — repeated for at least 6 months to detect nephritis |
Immunodeficiency
- SCID: hematopoietic stem cell transplant (gene therapy for some types); protective isolation until then
- Antibody deficiencies: immunoglobulin replacement (IVIG every 3–4 weeks or subcutaneous weekly), lifelong
- Prophylactic antibiotics (e.g., trimethoprim-sulfamethoxazole against Pneumocystis) as indicated
- Live vaccines are contraindicated in SCID, significant T-cell defects, and high-dose immunosuppression (MMR, varicella, rotavirus, BCG, live influenza)
- Blood products for SCID and T-cell defects: irradiated (prevents graft-versus-host disease) and CMV-safe
- IgA deficiency with anti-IgA antibodies: IgA-deficient donor products or washed cellular products
- Complement deficiency: meningococcal and pneumococcal vaccines; prompt treatment of fever
Anaphylaxis
- Epinephrine IM into the mid-outer thigh immediately: 0.01 mg/kg of 1 mg/mL solution, maximum 0.3 mg in children (0.5 mg in adolescents and adults); repeat every 5–15 minutes if needed. Auto-injector doses: 0.1 mg (about 7.5–15 kg), 0.15 mg (about 15–30 kg), 0.3 mg (30 kg or more)
- Call for help; lay the child flat with legs raised (sitting up if breathing is hard; recovery position if vomiting); never stand or walk the child suddenly
- Oxygen, IV isotonic fluid boluses (10–20 mL/kg, reassessing after each) for hypotension
- Adjuncts after epinephrine: albuterol for wheeze, antihistamines for itching and hives; corticosteroids are not first-line. Antihistamines do not treat airway obstruction or shock
- Observe for a biphasic reaction; discharge with two epinephrine devices and an action plan
Food allergy prevention — introduce peanut-containing foods and other allergens around 4–6 months (after checking with the provider for infants with severe eczema or egg allergy).
Autoimmune disease
- SLE: hydroxychloroquine for all, corticosteroids, and immunosuppressants for organ disease
- JIA: NSAIDs, joint injections, methotrexate, biologics (TNF inhibitors)
- IgA vasculitis: supportive (rest, hydration, acetaminophen or NSAIDs if the kidneys are normal); corticosteroids for severe abdominal pain; kidney specialist for nephritis
Drug safety (doses weight-based and verified against a pediatric reference)
| Drug | Key safety points |
|---|
| Epinephrine | Tachycardia, pallor, tremor, anxiety — expected; no absolute contraindication in anaphylaxis; IM (not SC, not IV push of 1 mg/mL) |
| IVIG / SCIG | Infusion reactions (fever, chills, headache, hypotension, anaphylaxis): premedicate as ordered, start slowly, vital signs during infusion; aseptic meningitis, thrombosis, kidney injury; delays response to live vaccines |
| Corticosteroids (long term) | Weight gain, moon face, hypertension, hyperglycemia, infection risk, osteoporosis and fractures, growth slowing, cataracts, mood change; do not stop abruptly; no live vaccines at high doses (commonly 2 mg/kg/day or 20 mg/day or more of prednisone for 14 days or longer) |
| NSAIDs (ibuprofen, naproxen) | Take with food or milk; GI bleeding, kidney injury, rarely photosensitivity (naproxen) |
| Methotrexate (weekly) | Weekly, not daily; folic acid; CBC and liver tests; mouth sores, nausea; no live vaccines; teratogenic; avoid alcohol (adolescents) |
| TNF inhibitors | Serious infections — TB screening before starting; no live vaccines; injection-site reactions |
| Hydroxychloroquine | Retinal toxicity — baseline and yearly eye exams; GI upset; very toxic in overdose |
| Trimethoprim-sulfamethoxazole | Rash (Stevens–Johnson syndrome), bone marrow suppression, hyperkalemia; fluids; not under 2 months (kernicterus) |
| Antihistamines | Sedation or paradoxical excitation in young children |
Listed in priority order.
- Anaphylaxis — airway and circulation
- Give IM epinephrine first, then call for help; position, oxygen, IV access and fluids
- Reassess airway patency and hemodynamic stability (HR, BP, perfusion, SpO₂) after epinephrine; repeat the dose if no improvement
- Monitor for at least 4–6 hours (longer after severe reactions) for a biphasic reaction
- Infection prevention in immunodeficiency
- Strict hand hygiene by everyone; private room; protective environment (HEPA-filtered, positive-pressure room) for SCID and transplant patients; limit visitors with any illness; no fresh flowers or plants in the room
- Recognize infection early — fever may be absent; report subtle changes (poor feeding, lethargy, tachypnea)
- Avoid rectal temperatures; meticulous skin, mouth, and line care
- Safe food handling (washed produce, well-cooked meat and eggs, pasteurized dairy)
- Transmission-based precautions — for a child with meningococcal infection: droplet precautions until 24 hours of effective antibiotics; identify close contacts for antibiotic prophylaxis
- Medication and infusion safety — IVIG rate titration and monitoring; steroid and immunosuppressant monitoring
- Joint and skin care — warm baths and gentle range-of-motion for JIA stiffness; sun protection for SLE
- Monitoring organ involvement — BP, urinalysis, daily weight, edema (lupus nephritis, IgA vasculitis)
- Epinephrine auto-injector: carry two at all times; inject into the outer thigh (through clothing) at the first signs of a serious reaction, then call emergency services; check expiry dates; share an action plan with school. An FDA-approved nasal epinephrine spray (1 mg for 15 to under 30 kg; 2 mg for 30 kg or more) is an alternative to auto-injectors
- Read food labels; teach the child age-appropriate avoidance; medical ID
- Immunodeficiency: no live vaccines for the child; household members should receive inactivated influenza vaccine and other routine vaccines (ask about live vaccines for siblings); avoid crowds and sick contacts; call for any fever
- Long-term steroids: take with food at the same time daily; do not stop suddenly; report fever or infection; calcium and vitamin D; watch growth
- JIA: take NSAIDs with food; keep regular eye examinations even when joints are fine; stay active (swimming is ideal)
- SLE: sunscreen and protective clothing, adherence to hydroxychloroquine, yearly eye check, report swelling or foamy urine
- IgA vasculitis: urine tests and BP checks for months even after the rash fades
| Complication | What to watch for |
|---|
| Anaphylaxis / biphasic reaction | Recurrence of stridor, wheeze, hypotension hours later |
| Overwhelming infection | Lethargy, poor perfusion, tachypnea — often without fever |
| Meningococcal sepsis | Fever with petechial or purpuric rash, shock — minutes count |
| Transfusion anaphylaxis | IgA deficiency with standard blood products |
| Graft-versus-host disease | Rash, diarrhea, liver dysfunction (non-irradiated blood in SCID) |
| Lupus nephritis / IgA vasculitis nephritis | Hematuria, proteinuria, edema, hypertension |
| Uveitis (JIA) | Often painless — found only by eye exam; can cause vision loss |
- Innate immunity acts first (skin, complement, phagocytes); maternal IgG protects young infants
- SCID: severe infections and failure to thrive in infancy; no live vaccines; irradiated blood; protective isolation; stem cell transplant
- Wiskott–Aldrich: infections + thrombocytopenia + eczema
- IgA deficiency: risk of anaphylaxis to blood products — IgA-deficient or washed products
- Complement deficiency → recurrent meningococcal infection; meningococcal disease = droplet precautions and contact prophylaxis
- Anaphylaxis: IM epinephrine 0.01 mg/kg mid-outer thigh first; then assess airway and hemodynamics; antihistamines are adjuncts only
- Type I = anaphylaxis; type IV = TB skin test and contact dermatitis
- Long-term steroids: weight gain, moon face, hypertension, osteoporosis, infection risk; no live vaccines at high doses
- JIA: NSAIDs with food, methotrexate weekly with folic acid, regular slit-lamp eye exams
- IgA vasculitis: purpura on legs and buttocks — monitor urine and BP for kidney involvement
Country Notes
United States
- Newborn screening for SCID (TREC assay) is performed in all states.
- Epinephrine auto-injectors are available in several weight-based doses; many states allow schools to stock undesignated epinephrine. Nasal epinephrine spray (1 mg and 2 mg) is FDA approved as an alternative.
Philippines
- Children in the DOH Expanded Program on Immunization receive BCG at birth; BCG is a live vaccine and must not be given to infants with suspected SCID or other severe T-cell deficiency.