Pregnancy and the flu

“Pregnancy and the flu” is not a separate disease or diagnosis. It describes how pregnancy affects your risk from influenza, as well as decisions about vaccination, testing, and treatment.

Influenza, usually called flu, is a contagious infection caused by influenza viruses. It mainly affects the nose, throat, and lungs. It is different from the “stomach flu,” which usually refers to vomiting and diarrhoea caused by other infections.

Pregnancy changes the immune system, heart, and lungs. These normal changes help support the pregnancy, but they can also make it harder for your body to cope with influenza. Pregnant people are more likely to develop serious flu complications than people of the same age who are not pregnant.

Flu vaccination is recommended during pregnancy by major public health and obstetric organisations. If you develop possible influenza, prompt medical advice matters because antiviral treatment works best when started early.

Influenza spreads mainly through respiratory droplets and small airborne particles released when an infected person talks, coughs, or sneezes. It can also spread when contaminated hands touch the eyes, nose, or mouth.

Influenza often begins suddenly. The infection can cause fever, chills, cough, sore throat, headache, muscle aches, and marked tiredness. Not everyone has every feature, and some people with influenza do not have a fever. COVID-19 and other respiratory infections can cause similar problems, so symptoms alone may not identify the virus.

During pregnancy, your heart works harder and your body uses more oxygen. As the uterus grows, the lungs also have less room to expand fully. These changes help explain why a respiratory infection can have a greater effect during pregnancy.

An injected flu vaccine trains the immune system to recognise selected influenza viruses without causing influenza. Antibodies made after vaccination can cross the placenta. This may also give the baby some protection during the first months after birth, before the baby is old enough for routine flu vaccination.

The injected inactivated or recombinant flu vaccines may be given during any trimester. The nasal-spray vaccine contains weakened live viruses and is not recommended during pregnancy. Recommendations may differ after pregnancy, so ask a clinician or pharmacist which product is suitable for you.

Most pregnant people who develop influenza recover, but pregnancy increases the chance of complications requiring medical care or hospital treatment. The risk continues for a short time after the pregnancy ends, while the body returns to its non-pregnant state.

Vaccination lowers the chance of influenza and can reduce the risk of severe illness. Because the influenza viruses in circulation change, a new seasonal vaccine is generally offered each flu season. A previous flu infection or an older vaccination does not reliably protect against the viruses expected in a later season.

If influenza is suspected, a clinician may recommend an antiviral medicine. Antivirals like acyclovir or oseltamivir act against the influenza virus; they do not treat every cause of cough or fever. Oseltamivir is the preferred antiviral during pregnancy in US guidance because it has the most pregnancy safety and benefit information.

Treatment should usually begin as soon as possible and should not be delayed solely while waiting for a test result. It may still help when started later, especially if illness is severe or worsening. Antiviral treatment can be used during any trimester when clinically indicated.

Fever during pregnancy also deserves attention. Ask your prenatal clinician how to manage it safely. Check before using a cold or flu product because combination products may contain several medicines, including duplicate pain or fever medicines.

Influenza can sometimes lead to pneumonia, an infection and inflammation in the lungs. It can also worsen asthma or heart disease. Severe cases may cause low oxygen levels, respiratory failure, dehydration, or a secondary bacterial infection.

Serious illness and high fever during pregnancy may also be associated with pregnancy complications, including preterm labour or preterm birth. This does not mean that these outcomes will happen whenever someone has flu.

Contact your prenatal or primary care service promptly—ideally the same day—if you are pregnant and develop possible influenza, particularly fever, cough, body aches, or sudden severe tiredness. This is urgent advice about timely assessment and possible antiviral treatment; it does not necessarily mean you need emergency care.

Seek emergency help for:

• Severe trouble breathing, blue or grey lips, or chest pain or pressure
• Confusion, a seizure, fainting, or difficulty waking
• Signs of severe dehydration, such as being unable to keep fluids down or barely urinating
• Symptoms that improve but then return with worse fever or breathing problems
• Heavy vaginal bleeding, leaking fluid, regular painful contractions, or markedly reduced fetal movement

Use your local emergency number or maternity emergency service for these problems. If you are unsure about fetal movement, follow the instructions your maternity service has given you rather than waiting for a routine appointment.

At a routine prenatal appointment, ask whether the current seasonal flu vaccine is available and which vaccine is appropriate. You do not need to wait for a particular trimester to receive an eligible injected flu vaccine.

If you have a history of a severe allergic reaction to a vaccine or one of its ingredients, tell the person providing the vaccine. They can review the exact product and decide where it can be given safely. An egg allergy does not automatically mean you cannot receive a flu vaccine.

If you develop a flu-like illness:

• Record when the symptoms began, your temperature, and any medicines taken
• Contact a prenatal or primary care service promptly
• Mention that you are pregnant and how many weeks pregnant you are
• Ask whether antiviral treatment should start before test results return
• Ask which fever, pain, cough, or cold medicines are suitable in pregnancy
• Drink fluids as tolerated and monitor fetal movement as advised

A clinician may diagnose influenza from your symptoms and local flu activity. When testing is useful, molecular tests can detect influenza genetic material in a nose or throat sample. Rapid antigen tests are faster but can miss infections. A negative rapid test may not rule out influenza, particularly when flu is circulating widely.

For routine follow-up, tell your prenatal clinician about the illness and any medicines prescribed. If you are recovering normally and have no pregnancy concerns, no special test is automatically required solely because you had influenza.

Can the injected flu vaccine cause flu?

No. Injected flu vaccines do not contain influenza virus capable of causing flu. Temporary arm soreness, tiredness, headache, or a mild fever can occur as the immune system responds.

Is the vaccine safe in early pregnancy?

Major public health and obstetric guidance supports eligible injected flu vaccination during any trimester, including the first trimester. The nasal-spray vaccine is not used during pregnancy.

Do I need a flu test before receiving treatment?

Not always. A clinician may recommend treatment based on your symptoms, pregnancy, and influenza activity in the community. Testing can be helpful, but waiting for a result should not unnecessarily delay treatment.

What if I had the flu vaccine but still become ill?

Contact a clinician promptly. Vaccination does not prevent every influenza infection, and other respiratory viruses can cause similar symptoms. You may still need testing or antiviral treatment.

Can I take antibiotics like amoxicillin or doxycycline for flu?

Antibiotics do not treat influenza because influenza is caused by a virus. They may be needed if a clinician identifies a bacterial complication, such as some types of pneumonia.

What if I become ill shortly after giving birth?

Tell your maternity or primary care service. The increased risk from influenza does not end immediately after delivery. Prompt assessment remains important, especially during the first two weeks after birth or if you have breathing problems.