Chickenpox (varicella) exposure letters to parents
A chickenpox case is mostly date arithmetic. When was the child infectious, which contacts are susceptible, how long is the prophylaxis window, and on what day does the watch period end. Get the dates right and the letters write themselves; get them wrong and you have either alarmed a school unnecessarily or missed a window that mattered.
| Marker | Counted from | Typical offset | Your date | What it decides |
|---|---|---|---|---|
| Rash onset in the index case | — | Day 0 | ____ | The anchor for every other row |
| Start of infectious period | Rash onset | 1–2 days before | ____ | Which contacts were actually exposed |
| End of infectious period | Rash onset | When all lesions have crusted | ____ | When the index case may return |
| Vaccine post-exposure window | First exposure | Within 3 days; may be considered up to 5 | ____ | The urgent deadline in the first letter |
| Immunoglobulin window | First exposure | Up to 10 days, for specified high-risk contacts | ____ | Directed by a provider, not the school |
| Earliest symptom onset in contacts | Exposure | Around day 10 | ____ | Start of the watch period |
| Latest symptom onset in contacts | Exposure | Around day 21 | ____ | End of the watch period; the date families want |
| Extended watch after immunoglobulin | Exposure | Around day 28 | ____ | Applies only to contacts who received IG |
| All-clear decision point | Last case | Two incubation periods | ____ | When you write the closing letter |
Offsets are the commonly published intervals and are given so you can size a window before your health department calls back. Exclusion of susceptible contacts, if your jurisdiction requires it, is directed by the health department and the exact days differ — do not exclude a student on the basis of this table alone. Prophylaxis decisions belong to a provider.
The eleven letters
1. General classroom notice. The baseline. States the case, the watch window with a dated end, the symptom picture, and the request that families call before bringing a child with a rash into a waiting room.
2. Targeted letter to families of susceptible students. The most important one, and the one requiring the most care. Sent only to households whose child's immunization record does not show evidence of immunity. It states plainly that the record shows the child may not be protected, that there is a time-limited option their provider may discuss with them, and that the family should call their provider today rather than tomorrow. Do not describe it as an instruction to vaccinate — that is a clinical decision, and framing it as a school directive is both wrong and counterproductive with families who hold exemptions.
3. Letter to families of immunocompromised students. You will not reliably know who these are, which is why the general notice should always carry the line inviting families with a specific concern to call. Where a student is already known to the health office, this letter should be preceded by a phone call, not replaced by it.
4. Pregnant staff and pregnant guardian notice. Notify staff generally rather than trying to identify who is pregnant. The letter says a case exists, that anyone who is pregnant or may be should speak to their own provider, and gives the exposure dates so the provider has something to work with.
5. Shingles source case in an adult. Worth its own variant because it confuses everyone. A person with shingles can transmit varicella to someone without immunity, through contact with the fluid from the lesions rather than through the air in the way chickenpox spreads. Covered lesions substantially reduce that risk. Say this plainly, because the alternative is a school convinced a staff member has caused an outbreak.
6. Breakthrough varicella. A vaccinated child can get a milder case with fewer lesions, which families read as evidence the vaccine failed. One sentence handles it: Chickenpox in a vaccinated child is usually much milder, with fewer spots and a shorter illness. That is the vaccine working, not failing.
7. Exclusion letter to the affected family. Return criterion stated as a test the parent can apply: all lesions crusted over, or where lesions do not crust, no new ones for 24 hours. Not "when the doctor says so" — the family needs to be able to look and know.
8. Return-to-school clearance. Confirms the return date in writing.
9. Prophylaxis deadline reminder. Short, urgent, sent the day after variant 2 to households that have not responded. The window for the option your provider may discuss with you closes on [DATE]. If you have already spoken to them, please ignore this.
10. Outbreak declared. When the health department declares one, they lead. The letter goes out under district letterhead with their input and states what changes — which may include exclusion of susceptible students.
11. All-clear. Sent after two incubation periods with no new cases. Names the date the watch period ended so families stop worrying.
What counts as evidence of immunity
Building the susceptible list is the part of this job that takes the time, and it is worth being precise about what ends a student's place on it.
- Two documented doses of varicella vaccine, appropriately spaced, is the standard evidence for children.
- Laboratory evidence of immunity — serology showing immunity, or laboratory confirmation of past disease.
- A healthcare provider's diagnosis or verification of past varicella or herpes zoster. Note that this is a provider's statement, not a parent's recollection.
- Birth in the United States before 1980 is used as presumptive evidence of immunity for adults in many contexts, with exceptions for healthcare personnel, pregnant women and immunocompromised people. It is relevant to staff, not to students.
What does not count, and is offered constantly: a parent's belief that the child "had it as a baby" without a provider record, a sibling's documented case, or a single dose where two are indicated. None of those is a reason to be rude about it — but none of them takes a student off the list, and the letter should say what would.
One practical warning. The susceptible list is built from immunization records, which means it is only as good as your records, and it is a list of children whose families may hold strong views about vaccination. Handle it as sensitive data: it should not be printed and left on a desk, it should not be emailed to a distribution list, and the letters generated from it should be individually addressed rather than sent as a visible group.
The first-hour sequence
When a chickenpox case is reported to the health office:
- Confirm what you actually have. Parent report of a rash is not a case. Ask whether a provider has diagnosed it and when the rash appeared — the onset date is the anchor for everything else.
- Report it if your state requires it. Varicella is reportable in most states. Make that call before you write anything, because the health department may direct the notification and may have context you lack.
- Fill in the date grid. Ten minutes, and it determines who is in the exposed group and what your deadlines are.
- Define the exposed group. Classroom, shared spaces, bus, activities. Be honest about where the child actually was during the infectious period rather than defaulting to the homeroom.
- Build the susceptible list from immunization records for that group.
- Send the general notice to the exposed group and the targeted letter to susceptible households on the same day. The prophylaxis window is short enough that a day matters.
- Log everything — what was sent, to whom, when, in which language, and what came back.
The mechanics in Kastr, and the gap. The two sends are two audiences, both built by selecting students — there is no classroom or grade preset, so this is manual selection either way. Guardians attach automatically once students are selected, which is the part that saves real time. Save the exposed group as a reusable audience preset before you send the first letter; you will need it again for the reminder and the all-clear. Every send lands in the per-district append-only audit log, hash-chained with SHA-256, so the record of who was notified and when is tamper-evident — which matters here more than usual, because exclusion decisions attached to immunization status are the ones that get challenged.
Short forms
SMS, general notice. [SCHOOL]: a case of chickenpox has been confirmed in your child's class. Watch for fever and a blistering rash through [DATE]. Call your provider before visiting if a rash appears. Details emailed.
SMS, susceptible household. [SCHOOL] health office: our records suggest [STUDENT] may not be protected against chickenpox, and there has been a case at school. Please call your provider today. Call me on [PHONE].
60-second voice, general. This is [NAME], the school nurse at [SCHOOL]. A case of chickenpox has been confirmed in your child's classroom. Chickenpox starts with a fever and tiredness, followed by an itchy rash that turns into small blisters. If your child is going to develop it, it would most likely be between [DATE] and [DATE] — after that date, the watch period is over. If a rash appears, please call your doctor's office before going in, so they can avoid other patients in the waiting room, and please let me know. If your child has a condition that weakens their immune system, or if anyone in your household is pregnant, please call me directly on [PHONE] today. Thank you.
Spanish, general. Estimadas familias: se ha confirmado un caso de varicela en el salón de su hijo o hija. La varicela comienza con fiebre y cansancio, seguidos de un salpullido con comezón que se convierte en ampollas pequeñas. Si su hijo o hija llegara a contagiarse, los síntomas aparecerían muy probablemente entre el [FECHA] y el [FECHA]. Después de esa fecha, ya no hay riesgo por este contacto. Si aparece un salpullido, llame al consultorio de su médico antes de ir, para que puedan proteger a otros pacientes, y avísenos. Si su hijo o hija tiene una condición que debilita el sistema inmunitario, o si alguien en su hogar está embarazada, por favor llámeme hoy al [TELÉFONO].
Questions people actually ask
How long is a student with chickenpox excluded from school?
The usual criterion is until all lesions have crusted over, or where lesions do not crust, until no new ones have appeared for 24 hours. Write it as a test the parent can apply by looking, not as a number of days — the duration varies by child and a fixed day count either returns someone too early or keeps a well child home. Confirm the wording against your state health code.
Do we exclude unvaccinated students who were exposed?
Sometimes, and it is not the school's decision alone. Some jurisdictions direct exclusion of susceptible contacts for a defined watch period after exposure, and that direction comes from the health department. Do not exclude on the basis of a published table: report the case, take their direction, and keep a written record of what you were told and by whom, because exclusions tied to immunization status get challenged.
How do we notify pregnant staff without violating anyone's privacy?
Notify all staff that a case exists, give the exposure dates, and ask anyone who is pregnant or may be to speak with their own provider. That way nobody has to disclose a pregnancy to the district in order to receive the information they need. The same approach works for pregnant guardians: put the invitation in the general letter rather than trying to identify households.
Does a staff member with shingles have to stay home?
Shingles can transmit varicella to a person without immunity, but through contact with the fluid in the lesions rather than the airborne route chickenpox uses, and covering the lesions substantially reduces the risk. Whether a particular staff member should be at work is a decision for them and their provider, informed by where the lesions are and what their role involves. Say this plainly in the letter, because otherwise a school concludes one staff member caused an outbreak.
A vaccinated student got chickenpox. Does that mean the vaccine failed?
No. Breakthrough varicella in a vaccinated child is typically much milder, with far fewer lesions and a shorter course, and that is the vaccine doing its job rather than failing. Put that sentence in the letter, because a breakthrough case circulating in a parent group chat does more damage to vaccine confidence in a school community than almost anything else.
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