The clock starts at exposure
Preventive antivirals should start as soon as possible, ideally within 48 hours of contact with the sick person.[2] If someone at very high risk lives with you, call their clinician today.
Who should consider a preventive antiviral
The IDSA guideline says clinicians can consider preventive treatment after a household exposure for:[2]
- adults and children 3 months and older who are at very high risk of complications, such as people who are severely immunocompromised, especially when the vaccine is not an option or may not work well; and
- unvaccinated household members of someone at very high risk, along with getting them vaccinated.
For people at higher risk more broadly, such as those 65 and older, pregnant people, or people with conditions like asthma, diabetes, or heart disease, ask a clinician the same day.[6] An alternative the guideline also supports is to agree on a plan to start treatment right away if symptoms appear.[2]
Children who were exposed should be assessed by their pediatrician.
Two options compared
| Oseltamivir (Tamiflu, generic) | Baloxavir (Xofluza, generic) | |
|---|---|---|
| How taken | Once a day by mouth[3] | One dose by mouth[1] |
| How long | 7 days after the last known exposure[1] | Single dose, within 48 hours of contact[1] |
| Ages | CDC supports prevention from 3 months of age; children are dosed by weight[1] | 5 years and older[5] |
| Not recommended | Doses are reduced for kidney disease[3] | During pregnancy, while breastfeeding, or alone for someone severely immunocompromised[1] |
| Watch out for | Nausea; taking it with food helps[3] | Do not take with dairy, calcium-fortified drinks, antacids, or supplements with calcium, iron, magnesium, or zinc[4] |
The Tamiflu label lists a longer course for household prevention than CDC does; FluHub follows CDC's 7 days.[1]
Treating the sick person may also help
In a 2025 trial, people with flu who took a single dose of baloxavir within 48 hours passed lab-confirmed flu to household members less often than those given placebo (9.5% versus 13.4% by day 5). The difference in household members who developed symptoms was smaller and not statistically clear.[10]
Steps that help everyone
- Separate. The sick person should stay home and away from others, including people they live with who are not sick.[7]
- Cleaner air. Take steps for cleaner air in shared spaces.[7]
- Masks and hygiene. A well-fitted mask for the sick person around others, frequent handwashing, and covering coughs.[7]
- Mind the timing. The sick person is most contagious in the first 3 days, and household members usually get sick 1 to 4 days after exposure if they are infected.[8][9]
- Vaccinate. A flu shot takes about two weeks to build protection, so it will not stop an infection from this exposure, but vaccination is still worthwhile while flu is circulating.[12] Everyone who cares for a baby should be vaccinated.[11] Flu vaccines.
- A note on the nasal spray vaccine. It should not be given within 48 hours after oseltamivir or 17 days after baloxavir, because the antiviral can stop it working.[1] The shot is not affected.