immunity can be assumed if:

key history taking

The diagnosis of chickenpox in the contact is certain.
The exposure was significant enough to put the person at risk of infection.
- Chickenpox.
- Disseminated zoster.
- Immunocompetent people with exposed lesions (for example ophthalmic zoster).
- Immunocompromised people with localized zoster on any part of the body (because this group may have increased viral shedding).
- Maternal/neonatal contact.
- Continuous home contact.
- Contact in the same room for 15 minutes or more, or contact on large open wards (particularly paediatric wards).
- Face-to-face contact (for example having a conversation).
The person has had chickenpox in the past.
The person is at increased risk of complications of chickenpox (for example pregnant women, immunocompromised people, and neonates).
The person is in contact with others at high risk of complications (for example healthcare workers).

uncertain or no previous history of chickenpox, or who come from tropical or subtropical countries, who have been exposed to infection - determine VZV immunity or non-immunity.
Not immune: post-exposure prophylaxis with aciclovir
- day 7-14 post exposure
- If aciclovir is contraindicated, give VZIG up to 10 days after contact
Non-immune pregnant women who have been exposed to chickenpox should be managed as potentially infectious
- from 8–28 days after exposure if they receive VZIG and
- from 8–21 days after exposure if they do not receive VZIG.
Further exposure without seroconversion - 2nd course antiviral from 7 days after exposure, or 2nd VZIG if exposure > 3/52 after last dose
Aciclovir = best interest. Not licensed in pregnancy.