Is there anything that can be done before a person falls ill? Yes. It is called post-exposure prophylaxis, it is simple, and it has to be asked for — nobody will know you were exposed unless you say so.
Who counts as exposed. According to the World Health Organization, a person who in the previous 10 days:
- was within 2 metres of someone with pneumonic plague — suspected or confirmed — at any time between that person's first symptom and the end of their first 48 hours of treatment;
- lives in the same household as a patient with bubonic plague, and so was probably exposed to the same fleas;
- handled an infected animal, or its tissues or body fluids, without protection;
- had a laboratory accident involving the bacterium.
What is done.
- A 7-day course of an antibiotic — a fluoroquinolone or doxycycline — prescribed by the health service. Not bought and taken on your own judgement: the medicine, the dose and the duration matter, and so does the record that you were treated.
- No isolation while you are well. The World Health Organization is explicit that exposed persons do not need to be isolated as long as they have no symptoms. Some authorities ask a contact who declines the antibiotic to stay at home for 7 days.
- Watching for symptoms. Take your temperature every day for at least 7 days. At the first fever, call — do not wait to see how it develops, and say that you are a contact.
- Fleas. Where fleas were the source, the clothing, the home and the pets are treated for fleas.
What you are asked to do.
- Tell the health service everything about the exposure: where, when, how close, for how long.
- Give the names of the other people who were there. They need the same offer, within the same 10 days.
- Take every dose.
- Carry on with ordinary life unless you are told otherwise.
What is not done.
- Antibiotics in advance, "just in case". Preventive antibiotics before any exposure are meant only for teams that have to work for a short time where plague is active — and for them from 1 day before until 48 hours after. They are not advice for travellers or households.
- Vaccination after an exposure. There is no vaccine for this purpose.
- Testing a healthy contact. There is no test that shows whether a person without symptoms is incubating plague.
Why the offer is made so widely. For the antibiotic to prevent the disease it has to be given during the incubation period, before anyone knows who would have fallen ill. So it is offered to every close contact, most of whom would have stayed well. That is the price of the method, and it is a small one.
Source. WHO, Manual for plague surveillance, diagnosis, prevention and control (2024), section 6.5, https://www.who.int/publications/i/item/9789240090422 ; New South Wales Health, Plague control guideline, https://www.health.nsw.gov.au/Infectious/controlguideline/Pages/plague.aspx ; United States Centers for Disease Control and Prevention, Clinical care of plague, https://www.cdc.gov/plague/hcp/clinical-care/index.html
What this is not. Reading, not a prescription. Whether you count as a contact and what you are given are decisions of the health service of the place you are in.