Module 3 · Chapter 3
Adverse Events Following Immunization — Basics
Definitions, frequency and severity, expected reaction rates for every vaccine, the five cause-specific categories, immunization errors, stress responses, coincidental deaths and COVID-19 AEFIs.
Definition
Vaccines in national programmes are extremely safe and effective, but like any biological product, no vaccine is perfectly safe. The process of immunization is also a potential source of reactions.
Core definitionAn adverse event following immunization (AEFI) is any untoward medical occurrence which follows immunization and which does not necessarily have a causal relationship with the usage of the vaccine. It may be any unfavourable or unintended disease, symptom, sign or abnormal laboratory finding.
- Reported events may be true adverse events (caused by the vaccine or immunization process) or coincidental (only temporally associated).
- A vaccine reaction is an individual’s response to the inherent properties of the vaccine — it can occur even when the vaccine is prepared, handled and administered correctly.
- Any adverse medical event with onset after vaccination may be reported as an AEFI, whether or not it is a true AEFI.
3.1 Types of AEFI
(i) By severity
- Minor reactions (common)
- Serious and severe reactions (rare)
(ii) Cause-specific
- Vaccine product-related reaction
- Vaccine quality defect-related reaction
- Immunization error-related reaction
- Immunization-triggered stress response (ITSR)
- (+ coincidental event — Table 3.5)
Table 3.1 · Frequency categories
| Category | Rate | Percent |
|---|---|---|
| Very common | ≥ 1/10 | ≥ 10% |
| Common (frequent) | ≥ 1/100 and < 1/10 | ≥ 1% and < 10% |
| Uncommon (infrequent) | ≥ 1/1,000 and < 1/100 | ≥ 0.1% and < 1% |
| Rare | ≥ 1/10,000 and < 1/1,000 | ≥ 0.01% and < 0.1% |
| Very rare | < 1/10,000 | < 0.01% |
3.2.1 Common, minor vaccine reactions
Most reactions are minor and self-limiting. Local reaction, fever and systemic symptoms are part of the immune response; components such as adjuvants, stabilisers or preservatives can also cause reactions. A good vaccine gives the best immunity with minimal reactions. Standard case definitions are from the Brighton Collaboration (Annexure 2).
Table 3.2 · Non-serious AEs — UIP vaccines
| Vaccine | Local (pain, swelling, redness) | Fever > 38°C | Irritability, malaise, systemic symptoms |
|---|---|---|---|
| BCG | 90–95% | – | – |
| Hepatitis B | Adults up to 15%; children up to 5% | 1–6% | – |
| Hib | 5–15% | 2–10% | – |
| Measles / MR / MMR | ~10% | 5–15% | 5% (rash) |
| OPV | None | < 1% | < 1% |
| Pertussis (DTwP / Penta) | up to 50% | up to 50% | up to 55% |
| Pneumococcal conjugate (PCV) | ~20% | ~20% | ~20% |
| IPV | ~30% | – | – |
| Tetanus / DT / DTaP / Td | ~10% | ~10% | ~25% |
| JE (live attenuated) | 5–7% | – | 1% |
Table 3.3 · Non-serious AEs — COVID-19 vaccines
| Vaccine | Local | Systemic |
|---|---|---|
| Covishield | Very common: injection-site tenderness, pain, warmth, pruritus, bruising. Common: swelling, erythema, induration | Very common: headache, nausea, myalgia, arthralgia, fatigue, malaise, feverishness, chills. Common: pyrexia, influenza-like illness, asthenia, pain in extremities, vomiting, diarrhoea. Uncommon: muscle spasms, abdominal pain, hyperhidrosis, pruritus, rash, urticaria, tinnitus, dizziness, somnolence, lethargy, paraesthesia, hypoaesthesia, decreased appetite, lymphadenopathy |
| Covaxin | Common: injection-site pain. Uncommon: pruritus, erythema, induration, swelling, tenderness | Common: pyrexia, fatigue, myalgia, headache. Uncommon: nausea, diarrhoea, vomiting, abdominal discomfort/pain, chills, arthralgia, dizziness, oropharyngeal pain, pruritus, ocular hyperaemia, eye pain, asthenia, pain in extremity, musculoskeletal stiffness |
| Corbevax | Very common: pain. Common: erythema, pruritus, swelling. Uncommon: warmth, rash. Rare: irritation | Very common: myalgia. Common: headache, fatigue, pyrexia, chills, arthralgia, nausea. Uncommon: pain, upper abdominal pain, diarrhoea, vomiting, urticaria, pain in extremity, dyspnoea, somnolence |
| Sputnik Light | Very common: increased injection-site temperature | Very common: hyperthermia, injection-site tenderness, oedema, pruritus, asthenia, pain, malaise, pyrexia, decreased appetite. Common: nasal congestion, sore throat, rhinorrhoea, headache, asthenia, nausea, vomiting, dyspepsia. Rare: dizziness, syncope |
| Covovax | Very common: pain. Common: tenderness, erythema, swelling, induration | Very common: pyrexia. Common: myalgia, arthralgia, nausea, fatigue, pain, malaise, headache |
| iNCOVACC (intranasal) | Common: running nose, sneezing, nasal congestion, nasal pain, sore throat, lacrimation | Common: fever, headache, myalgia, fatigue, nausea and vomiting |
- Local reactions vary by antigen: very common (>10%) with whole-cell DTP but 1–10% with acellular DTP.
- BCG: a papule appears ≥ 2 weeks after vaccination, ulcerates and heals over months leaving a scar — a normal response, not an adverse event. Keloid from the BCG lesion is more common in Asian and African populations.
- Fever is a very common (>10%) systemic reaction for most antigens; irritability, malaise and loss of appetite also occur. DTwP causes more systemic reactions than DTaP.
- LAVs (measles/MMR, OPV): systemic reactions arise from vaccine-virus infection. Measles vaccine → fever, rash and/or conjunctivitis, much milder than wild measles but can be severe or fatal in severely immunocompromised people. OPV → diarrhoea, headache and/or muscle pain in < 1%.
Exam pearlExpected minor reactions are a measure of system sensitivity — their reporting rate indirectly shows how sensitive surveillance is. A rate significantly higher than expected needs investigation to exclude a vaccine quality defect or programme error.
3.2.2 Serious and severe vaccine reactions
“Serious” and “severe” are often used interchangeably — they are not the same.
Serious AEFI (regulatory term)
Meets any of: results in death; is life-threatening; requires in-patient hospitalization or prolongs existing hospitalization; results in persistent or significant disability/incapacity; is a congenital anomaly/birth defect; requires intervention to prevent permanent impairment or damage.
Figure 3.1 list: death · hospitalization · clusters · disability · congenital anomaly/birth defect · media reports / community or parental concern.
Severe AEFI (broader, non-regulatory)
Higher in severity than minor reactions but does not necessarily lead to hospitalization. May be disabling and rarely life-threatening, but most do not cause long-term problems. Must also be reported.
Examples: seizures, hypotonic hypo-responsive episodes (HHE), prolonged/persistent inconsolable crying, thrombocytopenia — “severe” if managed as out-patients. Fever can be low-grade or high-grade by severity.
Exam pearlAll serious reactions are severe, but not all severe reactions are serious. Anaphylaxis is always serious and life-threatening, even if managed as an out-patient with quick recovery.
Table 3.4 · Frequency and nature of severe/serious AEs
| Vaccine | Reaction | Time to onset | Frequency |
|---|---|---|---|
| BCG | Local: abscess, keloid, cutaneous lesions, lymphadenitis, suppuration | 1–6 months | 1 per 1,000–10,000 |
| Osteitis / osteomyelitis | 1–12 months | 1 per 80,000 | |
| Disseminated BCG disease | 1.5–4.29 per 1,000,000 | ||
| Immune reconstitution syndrome (HIV patients) | 1 per 640,000 | ||
| OPV | Vaccine-associated paralytic poliomyelitis (VAPP) | 4–30 days | 1 per 6,400,000 |
| DTwP / Pentavalent (DTwP + Hib + HBV) | Fever >38°C and irritability · drowsiness | 0–24 h | 40–75% · 33–62% |
| Prolonged inconsolable crying (>1 h) | 0–24 h | 3.5% | |
| High fever >40.5°C | 0–24 h | 0.3% | |
| HHE | 0–48 h | 1–291 per 100,000 | |
| Seizure | 0–72 h | 8–60 per 100,000 | |
| Acute encephalopathy / encephalitis | 2–11 days | 1 per 310,000 to 5,300,000 | |
| Anaphylaxis / shock | 0–1 h (may be up to 24 h) | 1–2 per 1,000,000 | |
| DTaP + Hib + HBV | Fever >38°C and irritability · drowsiness | 0–24 h | 20.3% · 42.7% |
| Prolonged inconsolable crying (>1 h) | 0–24 h | 0–0.2% | |
| High fever >40.5°C | 0–24 h | 0.9% | |
| HHE | 0–24 h | 14–62 per 100,000 | |
| Seizures | 0–24 h | 0.5 per 100,000 | |
| Anaphylaxis | 0–1 h (up to 24 h) | 1 per 1,000,000 | |
| Hepatitis B | Anaphylaxis | 0–1 h (up to 24 h) | 1.1 per 1,000,000 |
| Measles / MR | Fever >39.4°C | 7–12 days | 5–15% |
| Rash | 7–10 days | 2–5% | |
| Febrile seizure | 6–11 days | 1 in 2,000–3,000 | |
| Thrombocytopenia | 12–25 days (range 1–83) | 1–40 per 1,000,000 | |
| Anaphylaxis | 0–1 h | 1–3.5 per 1,000,000 | |
| Encephalopathy / encephalitis / encephalomyelitis | 8–9 days | 1 per 1,000,000 | |
| Rubella | Arthralgia / arthritis / arthropathy | 1–3 weeks | 10–25% (mostly adults) |
| Mumps | Aseptic meningitis | 2–3 weeks | 13–900 per 1,000,000 |
| MMR | Febrile seizure | 5–12 days | 40 per 100,000 |
| Tetanus / Td | Brachial neuritis | 0–60 days | 0.69 per 10,000,000 |
| Anaphylaxis | 0–1 h | 1.6 per 1,000,000 | |
| Rotavirus | Intussusception | 1–7 days | 1–6 per 100,000 first doses |
| JE (SA14-14-2, live) | Serious allergic reactions | 0–2 weeks | 10–1,000 per 1,000,000 |
| JE (inactivated) | Serious allergic reactions | 0–2 weeks | 10–1,000 per 1,000,000 |
| Seizures (0–2 days); encephalopathy, neuropathy, myelitis, aseptic meningitis (3–42 days) | 0–2 d / 3–42 d | 1 per 1,000,000 (pooled) | |
| Influenza (inactivated) | Anaphylaxis | 0–1 h | 0.7 per 1,000,000 |
| Guillain-Barré syndrome | 2–7 weeks | 1–2 per 1,000,000 | |
| Oculo-respiratory syndrome | 2–24 h | 76 per 1,000,000 | |
| Influenza (live attenuated) | Anaphylaxis (0–1 h), wheeze (0–42 days), GBS (2–7 weeks) | as listed | 2 per 1,000,000 |
| Varicella zoster | Febrile seizures | 7–10 days | 4 per 10,000 |
| HPV | Myalgia, arthralgia | – | 1–28 per 100 doses |
| Anaphylaxis | 0–1 h | 1.7 per 1,000,000 | |
| Rabies | Local: pain, redness, swelling, induration | 0–3 days | HDCV 21–74%; PCECV 4%; PVRV 7% |
| Systemic: fever, headache, dizziness, GI symptoms | 0–5 days | HDCV 7–55.6%; PCECV 15%; PVRV 6% | |
| Anaphylaxis | 0–1 day | 1 per 1,000,000 | |
| Guillain-Barré syndrome | 12–85 days | < 1 per 1,000,000 | |
| Yellow fever | Headache, myalgia, malaise, fever | 1–10 days | 15–31.4% |
| Injection-site pain, swelling | 19.9–39.4% | ||
| Viscerotropic disease | 2–5 days | 0.25–7.9 per 100,000 | |
| Neurotropic disease (encephalitis, meningitis, GBS) | 4–30 days | 1–8 per 100,000 | |
| Typhoid | Oral: gastrointestinal, fever | 0–5 days | 1.2–3.9% |
| Injectable: injection-site pain · erythema, induration, headache | 0–5 days | up to 80% · 3–7% | |
| Serious reactions | – | Not reported | |
| COVID-19 vaccines | Anaphylaxis | 0–1 h (may be up to 24 h) | 5 per 1,000,000 doses |
| Covishield | Thrombosis with thrombocytopenia syndrome (TTS) | 3–30 days | 0.5–6.8 per 100,000 |
| Thrombocytopenia | 10 days (1–78) | 8 per 1,000,000 |
High-yield windowsVAPP 4–30 days · HHE 0–48 h · DTwP seizure 0–72 h · MR fever/febrile seizure 6–12 days · MR thrombocytopenia 12–25 days · rotavirus intussusception 1–7 days · GBS (influenza) 2–7 weeks · anaphylaxis 0–1 h (up to 24 h) · Covishield TTS 3–30 days.
3.3 Cause-specific AEFIs (CIOMS/WHO 2018 — Table 3.5)
| Category | Definition |
|---|---|
| Vaccine product-related reaction | Caused or precipitated by a vaccine due to one or more inherent properties of the vaccine product. |
| Vaccine quality defect-related reaction | Caused or precipitated by a vaccine due to one or more quality defects of the product, including its administration device as provided by the manufacturer. |
| Immunization error-related reaction (formerly “programme error”) | Caused by inappropriate vaccine handling, prescribing or administration — by its nature preventable. |
| Immunization triggered stress response (earlier “immunization anxiety-related reaction”) | Arising from anxiety about the immunization. |
| Coincidental event | Caused by something other than the vaccine product, immunization error or immunization anxiety. |
“Immunization” = use of a vaccine to immunize; “usage” = all processes after the vaccine leaves the manufacturing/packaging site (handling, prescribing, administration). Cause-specific categorisation is important for decisions on the safety of a vaccine product.
3.3.1 Vaccine product-related reaction
Response to the vaccine’s inherent properties even when correctly prepared, handled and given — from an immune-mediated reaction or replication of the vaccine microbial agent (attenuated live virus/bacteria). Immune-mediated reactions are generally mild, but high-risk individuals may react unusually: e.g. vaccine fever can trigger a seizure in a child with a seizure disorder or febrile-seizure tendency. Other examples: anaphylaxis, allergic reactions.
3.3.2 Vaccine quality defect-related reaction
A defect arising during manufacture — e.g. insufficient inactivation of wild-type agent (wild polio virus) or a contaminant introduced in manufacture. Since Good Manufacturing Practices (GMP) and stronger NRAs, such defects are very low and extremely rare.
Case study · quality defect1955, USA: polio vaccine from Cutter laboratory → 40,000 people developed abortive polio, 200 permanently paralysed, 10 died. Two production pools of 12,000 doses contained live virus — defective inactivation.
3.3.3 Immunization error-related reactions
Errors in any process after the vaccine leaves the manufacturer: prescribing, preparation, handling, storage and administration. Formerly “programme error”. Preventable; they damage trust, so timely identification and correction matter.
Table 3.6 · Types of immunization error and related reactions
| Error | Examples | Related reaction |
|---|---|---|
| Error in prescribing / non-adherence to recommendations | Failure to adhere to a contraindication; failure to adhere to indication, dose or schedule | Disseminated infection with a live vaccine in an immunocompromised person; anaphylaxis in a person with known allergy; systemic and/or local reactions |
| Non-sterile injection | Reuse of disposable syringe/needle contaminating the vial (esp. multi-dose); improperly sterilised syringe/needle; contaminated vaccine or diluent; reuse of reconstituted vaccine in later sessions | Local injection-site reactions (abscess, cellulitis); sepsis, toxic shock syndrome; blood-borne transmission (hepatitis B or C, HIV); death |
| Error in reconstitution / use of vaccine with abnormal physical condition | Reconstitution with incorrect diluent (drug substituted for vaccine or diluent); vaccine with changed colour, turbidity, foreign substances; inadequate shaking; improper syringe filling | Effect of wrong diluent (e.g. insulin, oxytocin, muscle relaxants); death; local abscess; increased local reaction (induration, pain); loss of potency |
| Error in vaccine handling | Excess heat/cold during transport, storage or handling (incl. diluent); cold chain not maintained at session site or use beyond recommended time after reconstitution; freezing during transport; use after expiry | Systemic or local reactions from physical change (e.g. agglutination of aluminium excipients in freeze-sensitive vaccines); toxic shock syndrome; loss of potency |
| Error in administration | Incorrect technique/site (BCG/DPT/dT/TT given subcutaneously, injection into buttocks in infants or medially on thighs, wrong needle) | Local reaction or abscess; traumatic neuritis; neurological, muscular, vascular or bony injury; ineffective vaccine |
- Errors can cause clusters, usually linked to one provider, facility or an inappropriately prepared/contaminated vial; they can also affect many vials (e.g. frozen vials in transport → more local reactions).
- Historically the commonest error was infection from non-sterile injection (abscess, sepsis/TSS, HIV/HBV/HCV). Auto-disable (AD) syringes have greatly reduced this, but risk persists in mass campaigns/disasters with logistic shortages — prevent by planning and monitoring.
- Contaminated vaccine (usually Staphylococcus aureus): children become sick within a few hours — local tenderness and infiltration, vomiting, diarrhoea, cyanosis, high temperature. Bacteriology of the vial (if kept in cold chain) confirms the source.
- Sterile abscess ~1 per 100,000 doses with aluminium-containing vaccines, especially DTP; risk ↑ with inadequate shaking, superficial injection and frozen vaccine. Contamination → bacterial abscess. BCG abscess from subcutaneous instead of intradermal injection.
- Ignoring contraindications = immunization error. Refer uncertainty to a programme manager, paediatrician or physician — but do not over-react to false contraindications (missed opportunities, lower coverage, more disease). Precautions need individual case-based assessment.
Open Vial PolicyApplies to pentavalent, DPT, Td, hepatitis B, TT, OPV, IPV, PCV and certain rotavirus and JE vaccines. Write date and time of opening. Partially used vials can be used in more than one session up to four weeks after opening provided: (1) VVM is in usable stage; (2) not beyond expiry; (3) stored under cold chain in transport and storage; (4) septum not submerged in water or contaminated; (5) aseptic technique used to withdraw all doses.
To avoid / minimise immunization errors
- Reconstitute only with the diluent supplied by the manufacturer.
- Write date and time of reconstitution on the label.
- Do not use reconstituted BCG and measles-containing vaccine beyond 4 hours, or JE beyond 2 hours; discard any remaining reconstituted vaccine at the end of each session.
- For open-vial-policy vaccines, write date/time of opening on the label.
- No other drugs or substances in the immunization-centre refrigerator.
- Train and closely supervise workers on storage, reconstitution and administration.
- Pay attention to contraindications.
- Careful epidemiological investigation of AEFIs pinpoints causes and corrects practice.
Case study · immunization error2016, country A: three neonates given BCG from the same vial collapsed within minutes and died. Muscle relaxants were found in the vaccine refrigerator; probable cause — muscle relaxant used as BCG diluent.
3.3.4 Immunization triggered stress response (ITSR)
Reaction to fear or pain of injection, unrelated to vaccine content. Term used since 2018; covers the whole spectrum of a stress response, not just anxiety. Stress arises from the immunization process and involves physiological factors, psychological strengths/vulnerability, knowledge, preparedness and social context; more common in peer or occupational groups. (WHO 2019 manual on immunization stress-related response; Annexure 3 — biopsychosocial model.)
Manifestations: fainting, anxiety, vomiting, abdominal pain, breath-holding, etc.
- Fainting is relatively common, especially in children over five years; may include brief clonic jerks needing no treatment or investigation. Manage by placing recumbent; consciousness returns within 1–2 minutes, full recovery may take longer.
- Hyperventilation → light-headedness, dizziness, tingling around the mouth and hands; common in mass campaigns, where mass hysteria clusters can follow one person fainting.
- Younger children: vomiting is common; may scream or run away; breath-holding can cause brief unconsciousness before breathing resumes.
Measures for people at risk of vasovagal reaction
- Immunize seated or supine.
- Muscle-tensing: clutch a ball in the hand of the arm not used, during and after vaccination.
- Remain seated for at least 15–30 minutes afterwards.
- If vaccinated supine, sit/stand up only when free of vasovagal symptoms.
- Arrange the session site to minimise injury from falls due to syncope.
Reduce stress: clear explanation, short waiting times, comfortable room temperature, prepare the vaccine out of the recipient’s line of vision, privacy during the procedure.
People at risk of anxiety reactions
- Young age, particularly adolescents.
- History of anxiety reaction or vasovagal syncope with previous vaccination/injection, sight of blood, or injury phobia.
- Those who express fear of injections.
- Known anxious people or history of acute stress response.
- Those who received negative information (relatives, friends, trusted people, media, social media).
Identify and reassure them; vaccinate in privacy (at least behind a screen); distract; observe for syncope; if needed vaccinate supine and keep supine ≥ 15 minutes; a trusted, non-anxious familiar person may be present.
Do not confuseSyncope can be misdiagnosed as anaphylaxis — train workers to distinguish them. Even if one IM dose of adrenaline is given for syncope mistaken as anaphylaxis, the vaccinee is not harmed.
Case study · ITSR2019, country D: school MR campaign for 12–19-year-olds; 44 hospitalized on day one. 2 had generalized urticaria and itching (vaccine product-related); 42 had hyperventilation and/or vomiting (ITSR). All discharged the same day.
Prevention and treatment of vaccine reactions
Common, minor reactions
- Advise parents on managing minor reactions and when to seek care — this reassures them.
- Syrup paracetamol 125 mg/5 ml, 10–15 mg/kg every 4–6 hours, maximum 4 doses in 24 hours for pain/fever after UIP vaccination in infants.
- Tepid sponging or bath, light clothing, extra fluids; cold compress at the injection site for local pain.
- Prophylactic paracetamol to prevent expected fever is NOT recommended (Annexure 4).
- Local remedies are strongly discouraged; early care by a qualified MO.
Anaphylaxis
- Every recipient should wait at least 30 minutes after vaccination for observation.
- Suspected anaphylaxis: the vaccinator gives one age-appropriate dose of injection adrenaline IM immediately, then transfers the patient to the nearest AEFI management centre/facility with a doctor (Annexure 5).
- An anaphylaxis kit with injection adrenaline at every session site. Adrenaline given for suspected anaphylaxis that proves not to be anaphylaxis is safe; in true anaphylaxis it is life-saving.
- Adrenaline has a short expiry → kits certified once a quarter by the PHC MO.
- AEFI management centres need AEFI management kits, trained doctors and resuscitation equipment (oxygen cylinders, endotracheal tubes, ambu-bags).
- Reference: Operational Guidelines for Initial Management of Anaphylaxis using Injection Adrenaline by ANMs, 2018, MoHFW.
3.3.5 Coincidental events
- Occur after vaccination but are not caused by the vaccine or its administration.
- Most vaccines are given in infancy, when congenital and neurological problems become apparent and infections are common — so many events (even deaths) are temporally linked and may be falsely attributed by chance. Inevitable with millions of doses.
- Still need investigation to allay fear and maintain credibility.
- Background rates help. If the same/similar events affected others of the same age at the same time who did not receive the vaccine → coincidental more likely.
- Greater awareness and new-vaccine introductions increase notification of coincidental events — these must be distinguished from potential signals.
Case studies · coincidental
- 2016, country E: DPT campaign during a diphtheria outbreak; a 5-year-old girl died 2 days after DPT with convulsions — she had prior convulsions and neurological symptoms → coincidental.
- 2017, country F: four infants died within 48 h of pentavalent; vaccine temporarily suspended; 3 confirmed coincidental (1 suffocation, 2 underlying infections), 1 inconclusive.
- 2018, country G: a 4-month-old died after DTwP; six severe local reactions with the same batch within a week; lot suspended; toxicity and sterility testing at national and WHO-accredited labs → death coincidental, six local reactions immunization error-related.
Table 3.7 · Expected coincidental infant deaths vs DPT/pentavalent doses (2021 estimates)
| Country | IMR /1000 | Births/yr | Infant deaths: month · week · day | PVV/DTP doses: month · week · day |
|---|---|---|---|---|
| Canada | 4 | 3,74,000 | 125 · 29 · 4 | 83,813 · 19,342 · 2,756 |
| China | 5 | 1,08,82,000 | 4,534 · 1,046 · 149 | 24,36,208 · 5,62,202 · 80,095 |
| India | 25 | 2,31,14,000 | 48,154 · 11,113 · 1,583 | 50,70,634 · 11,70,146 · 1,66,706 |
| Indonesia | 19 | 44,96,000 | 7,119 · 1,643 · 234 | 9,92,380 · 2,29,011 · 32,626 |
| Iran | 11 | 12,04,000 | 1,104 · 255 · 36 | 2,67,920 · 61,828 · 8,808 |
| Mexico | 11 | 18,82,000 | 1,725 · 398 · 57 | 4,18,792 · 96,644 · 13,769 |
| Sudan | 39 | 15,34,000 | 4,986 · 1,151 · 164 | 3,31,689 · 76,544 · 10,905 |
| United Kingdom | 4 | 6,77,000 | 226 · 52 · 7 | 1,51,716 · 35,011 · 4,988 |
Assumes uniform distribution of deaths and immunization; three-dose DTP/pentavalent schedule with 90% coverage per dose. Source: UNICEF State of the World’s Children 2023. Expected deaths may be inflated because terminally/very ill children are assumed to be immunized. Actual coincidental deaths depend on population size, IMR, number of immunization episodes and coverage; statistics can test whether observed vs expected differences are chance.
3.4 AEFIs following COVID-19 vaccines
- Developed and deployed within months; regulators granted Emergency Use Authorizations; some trial phases ran simultaneously; many used new/rarely used platforms → limited early safety information; frequent safety reviews and benefit–risk analyses needed.
- Common minor AEs in India: pyrexia, injection-site pain, swelling, redness, headache, dizziness, vomiting, fatigue, hypersensitivity.
- TTS (large clots + low platelets) seen at < 1 in 100,000 vaccinated after adenovector COVID-19 vaccines in India.
- Adverse Events of Special Interest (AESI): events identified for monitoring during roll-out, based on trial data and previous use of the same platform. Indian studies monitor: myocarditis, pericarditis, encephalitis, myelitis, seizures, idiopathic thrombocytopenia, Guillain-Barré syndrome, TTS and thrombosis.
- Overall, COVID-19 vaccines have a favourable benefit-to-risk ratio.
Chapter summary
- AEs may be vaccine product-related, quality defect-related or immunization error-related; ITSRs come from fear/pain, not the vaccine.
- Immunization errors (old “programme errors”) are avoidable.
- Coincidental events have only a temporal association.
- Antigen-specific background rates guide classification.
- Minor reactions need no special treatment; rare serious reactions need timely treatment by qualified staff.
- With novel vaccines, monitor AESIs.
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