Fever from influenza: what should you tell your doctor when asking about antiviral medicine?

Hello. I am Shunichi Gamo, MD, PhD, a board-certified pulmonologist and the director of Sendai International Airport North Clinic.

When influenza causes a fever, many people are unsure whether to use an antiviral medicine (a medicine that helps keep the virus from multiplying). You may also worry that it is already too late. This article explains what to tell your doctor when you ask about antiviral medicine. It also covers what the medicine can be expected to do, and the signs that mean you should seek medical care quickly, even before asking about medicine.

In the exam room, you will have only a short time to talk. Let’s go step by step through what to say and in what order.

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Fever from influenza: how soon should you ask about antiviral medicine?

If you want to ask about antiviral medicine for influenza, a general guide is to do so within 48 hours of when your symptoms began. A 2019 US review article (a paper that summarizes the research on a topic) says treatment can be considered for people who see a doctor within 48 hours of the start of symptoms. [1] The same review explains that the benefit of treatment is greatest when it is started within 24 hours of the first symptoms. [1]

At your visit, tell the doctor not only when you noticed the fever, but also when your first symptom appeared. With influenza, respiratory symptoms and muscle aches often start suddenly, and sometimes there is no fever. [2] For example, if your body started aching the night before and the fever came the next morning, tell your doctor about the night before as well. The 48-hour mark is not a fixed deadline for everyone. It is a guide the doctor uses when making a decision.

What to tell your doctor	Example of how to say it
When your first symptom appeared	“I’ve had chills and body aches since about 9 p.m. last night.”
When you noticed the fever, and your highest temperature	“It was 38.5°C at 6 a.m. this morning.”
Symptoms other than fever	“I have a bad cough and severe muscle aches, and my throat hurts too.”

If you don’t remember the exact time, just tell the doctor as best you can, for example, “sometime yesterday evening.”

Before your visit, write down two separate times: when you noticed your first symptom and when you noticed the fever.

How much can influenza antiviral medicine ease fever and other symptoms?

In patients with no other illnesses, the main thing to expect from influenza antiviral medicine is a shorter time until they get better. A US review says that anti-influenza medicines (such as oseltamivir) shorten the illness by about 24 hours. [1] The review also shows that they may lower the risk of serious complications (other illnesses that follow the original illness). [1]

The “about 24 hours” is a difference in how long it takes to get better. It is not a promise that your fever will go down on the day you take the medicine.

One trial, from the 2016-2017 season, looked at outpatients aged 12 to 64 who had no other illnesses. [3] People who took baloxavir had a shorter time until their symptoms eased than people who took a placebo (a dummy medicine with no active ingredient). [3] Compared with people who took oseltamivir, the time was about the same. [3]

At your visit, try asking, “In my case, how should I think about whether to use the medicine?”

More than 48 hours since influenza symptoms began: is it too late to ask?

Even after 48 hours, it is fine to ask your doctor. Whether to use the medicine depends on your symptoms at that time and any long-term conditions. Tell the doctor when your first symptom appeared and how your symptoms are changing now.

For children, there is guidance that can help. The American Academy of Pediatrics’ recommendations for the 2024-2025 season advise treatment for the following children. [4] These are children who are in the hospital or seriously ill, children whose symptoms keep getting worse, and children with long-term conditions that raise the risk of complications. [4] This applies no matter how long it has been since symptoms began. [4] These recommendations are for children in the US. They cannot be applied directly to adults or to medical care in Japan.

For adults too, many people who get influenza recover within a week. [2] Even if your symptoms are getting milder, see a doctor to check that you are recovering as expected, and talk with the doctor about whether to use medicine.

Even after 48 hours, seek medical care right away if you have trouble breathing or a change in alertness. If a long-term condition is getting worse, see a doctor the same day.

Can you ask about influenza antiviral medicine without having a test?

You can ask about antiviral medicine even if you have not had an influenza test. A US review says that in outpatient care, many patients are diagnosed with influenza based on their symptoms and an examination, and a test to confirm it is not required. [1] In Japan, actual practice differs from one medical facility to another. Testing may be useful for patients in the hospital, and for patients whose treatment plan would change once the diagnosis is confirmed. [1]

There are several kinds of tests, and tests that can detect influenza and the virus that causes COVID-19 at the same time are also in use. [2] A test is not a requirement for getting medicine. It is a tool used when the doctor wants to confirm the diagnosis.

At your visit, information about the people around you is also helpful. Tell the doctor whether anyone in your family or at work has been diagnosed with influenza, and when you were in contact with them. If you have already been tested at another medical facility, share that result too.

Before your visit, check the dates when people around you were recently diagnosed with influenza. If you have test results, bring the printout or have them ready on your screen. This makes them easier to share.

Asking about influenza medicine: why mention your age, long-term conditions and pregnancy?

Your age, any long-term conditions and whether you are pregnant help the doctor decide whether to use medicine, and which one. The American Academy of Pediatrics’ recommendations say that outpatient treatment may be considered for children who are not at high risk of complications. This applies if it can be started within 48 hours of the start of symptoms. [4] They also say treatment may be considered for children who have a younger brother or sister under 6 months old, or who live with a family member whose long-term condition makes complications more likely. [4]

Another trial looked at outpatients aged 12 or older with factors that make complications more likely (for example, being older than 65). In patients who had had symptoms for less than 48 hours, symptoms improved faster with baloxavir than with placebo. [5] In this trial too, the difference between baloxavir and oseltamivir was not large. [5] The researchers support early treatment for people who are more likely to develop complications. [5]

Women who are pregnant or have recently given birth may be at higher risk of complications, yet they have been left out of clinical trials of antiviral medicines. [6] In observational studies, pregnant and postpartum women treated with neuraminidase inhibitors such as oseltamivir had fewer severe outcomes. [6] There was also no increase in harm to the mother, fetus or newborn. [6] For baloxavir, there is not enough data on its safety and effectiveness during pregnancy and after childbirth, and a 2021 review does not recommend it for this group. [6] Talk with your doctor about which medicine to use, taking into account how many weeks pregnant you are.

What to tell your doctor	Why it matters
Age (children, people older than 65)	The approach to treating children depends on their age and condition. [4] Being older than 65 is one of the factors that make complications more likely. [5]
Whether you have any long-term conditions, and their names	Treatment is recommended for children with long-term conditions that raise the risk of complications, no matter how long it has been since symptoms began (American Academy of Pediatrics). [4]
Whether you are pregnant or have recently given birth, and how many weeks pregnant you are	In observational studies of pregnant and postpartum women, those treated with neuraminidase inhibitors had fewer severe outcomes. Baloxavir is not recommended during pregnancy or after childbirth. [6]
Ages and long-term conditions of the people you live with	Treatment may be considered for children who live with someone under 6 months old or someone with a long-term condition (American Academy of Pediatrics). [4]

If you have your medication record book (okusuri techō) or your Maternal and Child Health Handbook (boshi techō), bring it. At the start of the visit, tell the doctor about any long-term conditions, how many weeks pregnant you are, and the ages of the people you live with.

Fever from influenza: what signs mean you should seek medical care right away?

If an influenza fever comes with changes such as seeming dazed, having a seizure, or being slow to respond when spoken to, they are signs that you need to seek medical care right away. Asking about antiviral medicine can wait until after that. Most people recover within a week, but some develop serious or life-threatening complications. [2]

What you notice	What to do
Slow to respond when spoken to, confused or not fully awake, or having a seizure	Seek medical care right away, even at night, including at the emergency department. If the seizure continues, or the person does not regain consciousness, call 119 (Japan’s emergency number for an ambulance).
Trouble breathing, fast breathing, or a poor color in the lips or face	Seek medical care even at night. If the lips or face are a poor color, contact emergency services. Taking a video of the person’s breathing can make it easier to explain.
Unable to drink fluids, or hardly passing any urine	See a doctor the same day. Tell the doctor how much you were able to drink and when you last passed urine.
A fever that went down rises again, or cough or phlegm gets worse	See a doctor soon. If there is also trouble breathing, seek medical care even at night.

If even one of the signs in the table is present, put off asking about antiviral medicine and contact a medical facility first.

What notes should you prepare before seeing a doctor for influenza?

Your notes for an influenza visit are easier to write if you keep them to six items. These are: when your symptoms started; symptoms other than fever; illness going around near you; your age, long-term conditions and pregnancy; the medicines you take and any allergies; and what bothers you most right now. A note on your smartphone, written like the example below, is enough.

Item	Example note
When symptoms started	Chills at 9 p.m. last night, 38.5°C at 6 a.m. this morning
Symptoms other than fever	Cough, sore throat, muscle aches
Illness going around	Older child diagnosed with influenza 3 days ago
Age, long-term conditions, pregnancy	Have asthma, 20 weeks pregnant
Medicines and allergies	Bringing medication record book; names of medicines that did not agree with me in the past (if any)
What bothers you most right now	Hard to breathe, can’t drink water

If someone accompanying the patient speaks for them, please add what the patient cannot say (how they were during the night, how much they could drink, how slow they are to respond). For a child, it helps to describe how their energy level differs from usual.

Before your visit, get your six-item note ready so you can simply show it on your screen. In the exam room, it’s fine to look at your note while you talk.

Summary

• When you ask about antiviral medicine, tell the doctor when your first symptom began, as well as when you noticed the fever.
• In patients with no other illnesses, the medicine can be expected to shorten the time until they get better. It does not bring the fever down as soon as it is taken.
• Your age, long-term conditions, pregnancy and the situation of the people you live with are things to consider when deciding whether to use medicine.
• If there is a change in alertness, a seizure or trouble breathing, seek medical care right away, before asking about medicine.

Frequently asked questions

If I take influenza antiviral medicine, will my fever go down right away?

Not necessarily. In patients with no other illnesses, the medicine is reported to shorten the illness by about 24 hours. [1] If you still have a fever the day after taking it, don’t assume it isn’t working. Keep drinking fluids and resting. However, if you have trouble breathing or a change in alertness, seek medical care without waiting for the next day.

If more than 48 hours have passed since my symptoms began, is it too late to ask about antiviral medicine?

It is fine to ask. The doctor will decide whether to use medicine based on things like your symptoms and long-term conditions. For children, the American Academy of Pediatrics recommends treatment for those who are in the hospital or have long-term conditions, no matter how long it has been since symptoms began. [4] If you have trouble breathing or a change in alertness, do not put off seeing a doctor because of how much time has passed.

Can I use influenza antiviral medicine while I am pregnant?

Some medicines can be used. In observational studies, women who were pregnant or had recently given birth and were treated with neuraminidase inhibitors such as oseltamivir had fewer severe outcomes. [6] Harm to the mother or baby also did not increase. [6] Baloxavir is not recommended during pregnancy or after childbirth because there is not enough data. [6] At your visit, start by telling the doctor how many weeks pregnant you are.

If my influenza test is negative, can I still get antiviral medicine?

Even with a negative test, the doctor decides whether to use medicine by also looking at your symptoms and the examination. A US review says that for outpatients, influenza is often diagnosed from symptoms and an examination, and a test to confirm it is not required. [1] In Japan, the approach differs from one medical facility to another. If you describe in detail the illness going around near you and how your symptoms started, it is easier for the doctor to decide, taking the test result into account as well.

Disclaimer

This article provides general medical information. It does not replace an examination, diagnosis or treatment by a doctor. The content is based on medical knowledge at the time of publication, but the right approach differs with each patient’s condition and background.

If you are worried about your symptoms, please talk to your regular doctor or a specialist medical facility.

References

1. Gaitonde DY, Moore FC, Morgan MK. “Influenza: Diagnosis and Treatment.” Am Fam Physician, 2019 Dec 15; 100(12): 751-758. PMID: 31845781
2. Uyeki TM, Hui DS, Zambon M, Wentworth DE, Monto AS. “Influenza.” Lancet, 2022 Aug 27; 400(10353): 693-706. DOI: 10.1016/S0140-6736(22)00982-5 PMID: 36030813
3. Hayden FG, Sugaya N, Hirotsu N, Lee N, de Jong MD, Hurt AC, et al. “Baloxavir Marboxil for Uncomplicated Influenza in Adults and Adolescents.” N Engl J Med, 2018 Sep 06; 379(10): 913-923. DOI: 10.1056/NEJMoa1716197 PMID: 30184455
4. Committee on Infectious Diseases. “Recommendations for Prevention and Control of Influenza in Children, 2024-2025: Policy Statement.” Pediatrics, 2024 Oct 01; 154(4): e2024068507. DOI: 10.1542/peds.2024-068507 PMID: 39183669
5. Ison MG, Portsmouth S, Yoshida Y, Shishido T, Mitchener M, Tsuchiya K, et al. “Early treatment with baloxavir marboxil in high-risk adolescent and adult outpatients with uncomplicated influenza (CAPSTONE-2): a randomised, placebo-controlled, phase 3 trial.” Lancet Infect Dis, 2020 Oct; 20(10): 1204-1214. DOI: 10.1016/S1473-3099(20)30004-9 PMID: 32526195
6. Chow EJ, Beigi RH, Riley LE, Uyeki TM. “Clinical Effectiveness and Safety of Antivirals for Influenza in Pregnancy.” Open Forum Infect Dis, 2021 Jun; 8(6): ofab138. DOI: 10.1093/ofid/ofab138 PMID: 34189160