Adverse Events
Part of Vaccines
Recognizing, grading, and managing adverse reactions to vaccines — from expected local reactions to rare serious events.
Why This Matters
No medical intervention is without risk, and vaccines are no exception. Most adverse events following vaccination are mild, expected, and self-limiting. But some are moderate, some are rare and serious, and a very few are life-threatening. A vaccine administrator who cannot distinguish normal from abnormal, minor from serious, will either over-react to expected reactions (creating fear and reducing vaccination uptake) or under-react to serious events (missing treatable emergencies).
In post-collapse contexts, adverse event management matters for two additional reasons. First, post-collapse communities will be understandably skeptical of medical interventions — a single serious adverse event that is mismanaged or misattributed will destroy vaccination programs. Transparency and competent response to adverse events builds the trust that makes vaccination campaigns work. Second, the range of available treatments for adverse events is limited — knowing what can and cannot be managed with available resources is essential for informed consent.
Categories of Adverse Events
Expected Reactions (Not True Adverse Events)
These are predictable responses to vaccination and are signs that the immune response has been activated:
Local reactions:
- Injection site pain: occurs in most vaccinated individuals; begins within hours, typically resolves within 48 hours
- Redness (erythema): 1-2 cm diameter around injection site; resolves within 3-4 days
- Swelling: localized, resolves 3-5 days
- Induration (hardness): firm lump at injection site; can last 1-2 weeks for aluminum-adjuvanted vaccines
Systemic reactions:
- Low-grade fever (37.5-38.5°C): occurs in 10-30% of vaccinated individuals within 1-2 days; resolves within 48 hours
- Fatigue/malaise: moderate fatigue for 1-2 days
- Headache: mild, resolves within 24-48 hours
- Muscle aches: systemic myalgia for 1-2 days
Communication: inform every person being vaccinated that these reactions are expected and normal. Specifically tell them what to expect so they are not frightened when it occurs. A patient who expects soreness and mild fever will not panic; one who is not warned may believe something has gone seriously wrong.
Grading Adverse Events
| Grade | Description | Action |
|---|---|---|
| Grade 1 (Mild) | Minimal symptoms, no limitation of activity | Reassure, monitor |
| Grade 2 (Moderate) | Some limitation of activity, manageable without intervention | Symptomatic treatment, observe |
| Grade 3 (Severe) | Significant limitation, unable to perform daily activities | Active treatment required, close monitoring |
| Grade 4 (Life-threatening) | Immediate risk of death | Emergency response immediately |
Local Adverse Events
Abscess at Injection Site
A lump at the injection site that becomes progressively more swollen, painful, warm, and develops pus. Can occur from 2 days to several weeks after vaccination.
Causes:
- Non-sterile injection technique
- Contaminated vaccine
- Subcutaneous rather than intramuscular injection of a vaccine intended for IM route
- Individual sensitivity to adjuvant (aluminum compounds can cause sterile abscess)
Sterile abscess: no bacteria; caused by aluminum adjuvant. Firm, slowly growing, not warm or tender. Does NOT need drainage — draining introduces infection. Will resorb over weeks to months.
Septic abscess: bacterial. Warm, tender, purulent. Needs incision and drainage.
Treatment:
- Sterile abscess: watchful waiting, reassure patient it will resolve
- Septic abscess: clean the area, incise over the fluctuant center with a sterile blade, express pus, irrigate, pack, change packing daily
Severe Local Reaction
Redness and swelling extending significantly beyond the injection site (>10 cm diameter, whole arm swollen), associated with warmth and pain. May look alarming.
Usually resolves without treatment within 3-5 days. Apply cool compress. Willow bark tea for pain. Elevate the limb.
Does not require: antibiotics, incision, concern about secondary spread (unless signs of spreading cellulitis — red streaks, lymph node swelling, systemic fever).
Systemic Adverse Events
High Fever
Fever above 39°C following vaccination. Uncommon but occurs especially in young children after whole-cell pertussis vaccines.
Management:
- Willow bark tea or other available antipyretics
- Increased fluids
- Cool compresses
- Monitor closely for febrile seizures in children under 5
Usually resolves within 48-72 hours. If fever persists beyond 72 hours post-vaccination, investigate for coincidental infection (the vaccine did not cause a 5-day fever — something else is happening).
Febrile Seizure (Children)
Occurs in approximately 1 in 3,000 children after some vaccines (MMR has a known association). The seizure is caused by the fever itself, not by the vaccine acting directly on the brain.
Recognition: whole-body rhythmic jerking, loss of consciousness, duration typically <5 minutes
Immediate management:
- Place child on their side (recovery position)
- Clear area of anything that could cause injury
- Do not put anything in the mouth
- Time the seizure
- Stay calm — most febrile seizures stop within 5 minutes
After the seizure:
- Child will be drowsy for 30-60 minutes (post-ictal period) — this is normal
- Monitor temperature, treat fever aggressively
- Neurological assessment: does the child return to normal baseline within 1-2 hours?
A simple febrile seizure (brief, not recurring) after vaccination does not predict epilepsy. The prognosis for the child’s neurological development is unaffected.
Seek urgent assessment if:
- Seizure lasts more than 15 minutes
- Multiple seizures in one fever episode
- Child does not return to normal after seizure
Anaphylaxis
The most serious and immediately life-threatening vaccine adverse event. Rare — estimated 1-2 cases per million doses for most vaccines.
Onset: typically within 15-30 minutes of vaccination (which is why all vaccinated individuals should be observed for 30 minutes).
Recognition: the “3-system” pattern
Skin (most prominent in 80-90% of anaphylaxis):
- Generalized hives (urticaria) — raised, intensely itchy welts
- Flushing (redness) of skin
- Angioedema — swelling of lips, tongue, throat, eyelids
Respiratory:
- Stridor (high-pitched breathing sound) — laryngeal edema
- Wheezing — bronchospasm
- Increased respiratory rate, difficulty speaking
Cardiovascular:
- Rapid, weak pulse
- Falling blood pressure
- Pale skin (shock)
- Collapse, loss of consciousness
Not all features occur in every case. Skin findings alone without cardiovascular or respiratory involvement is NOT anaphylaxis — it is urticaria (allergic reaction), less serious.
Treatment — anaphylaxis is a medical emergency:
Step 1: Call for help. Do not leave the patient.
Step 2 — Epinephrine (adrenaline) IMMEDIATELY:
- Adult: 0.5 mL of 1:1000 (0.5 mg) intramuscular injection into outer thigh
- Child >12 years: 0.5 mg IM
- Child 6-12 years: 0.3 mg IM
- Child <6 years: 0.15 mg IM
- Can repeat every 5-10 minutes if response inadequate
Epinephrine is the only life-saving treatment for anaphylaxis. Everything else is supportive. If epinephrine is not available, the chances of surviving severe anaphylaxis are very low.
Step 3 — Position:
- If conscious: sitting upright (for respiratory symptoms)
- If unconscious or shock: flat with legs raised (unless breathing is difficult, in which case upright)
Step 4 — Airway: If patient cannot breathe through an obstructed airway (stridor, drooling, muffled voice), this is a cricothyroid emergency. A skilled person can make an emergency airway through the cricothyroid membrane (the soft indented area between the laryngeal cartilage and the tracheal cartilage) with a large needle or small incision.
Step 5 — If epinephrine not available:
- Antihistamine (diphenhydramine if available): treats skin manifestations, does NOT treat anaphylaxis
- Lay flat, legs elevated
- If available: corticosteroids reduce the late-phase response (hours later) but do not help the immediate reaction
- Manual CPR if heart stops
After anaphylaxis:
- The patient must NOT receive the same vaccine again without specialist evaluation
- Document all details: vaccine, lot number, reaction onset, treatment, outcome
- Inform the patient they need to carry epinephrine at all times
Vaccine Injury Versus Coincidental Illness
A common error — in both directions — is attributing every illness that occurs after vaccination to the vaccine. Post hoc ergo propter hoc (after this, therefore because of this) is a logical fallacy that causes harm when applied to vaccines.
A useful framework:
Temporally associated but not causally related: infections that were incubating at time of vaccination will manifest after vaccination. They appear “caused by” the vaccine but are not.
Vaccination-site reactions beginning within hours to days and confined to the injection site are almost certainly vaccine-related.
Systemic reactions within 48 hours (fever, malaise) are consistent with vaccine cause.
Any illness appearing more than 7-10 days after vaccination is unlikely to be directly caused by the vaccine (except certain live vaccine reactions — measles vaccine can cause a mild fever/rash at 7-12 days as the attenuated virus briefly replicates).
Documenting adverse events honestly — including both events that are vaccine-related and events that happen to occur near vaccination but are not — is essential for community trust. When the healer says “this rash 2 weeks after vaccination is a coincidence, not a vaccine reaction,” the community must trust that judgment based on a track record of honest, accurate reporting.
That trust is built by acknowledging real vaccine reactions fully and promptly when they do occur.