Understanding RSV: Who Is at High Risk, and Should Pregnant Women Get Vaccinated?

High-risk groups for RSV

Respiratory syncytial virus (RSV) is a common respiratory virus. Most people develop only mild symptoms, such as a runny nose, cough or fever. However, RSV can also cause bronchiolitis, pneumonia and breathing difficulties. Babies in their first six months of life are particularly vulnerable. Premature infants, children with chronic lung disease or congenital heart disease, and children with weakened immunity or difficulty clearing mucus are also more likely to develop severe illness. Even otherwise healthy young infants may need hospital treatment after an RSV infection.

Among adults, people aged 75 or above, residents of nursing homes, and those with chronic heart or lung disease are at higher risk. Other risk factors include kidney or liver disease, diabetes with complications, blood disorders and weakened immunity. RSV may also worsen asthma, chronic obstructive pulmonary disease (COPD) or heart failure.

In Hong Kong, RSV infections can occur throughout the year. Some years see increased activity between May and September. Hospital admissions mainly involve children under five, especially babies aged six months or younger, followed by older adults.

What are the benefits of RSV vaccination?

RSV vaccines are designed mainly to reduce the risk of severe lower respiratory tract disease and hospitalisation. They do not guarantee that a vaccinated person will never become infected. For older adults and other high-risk adults, vaccination may help reduce serious lung complications. In the United States, vaccination is recommended for everyone aged 75 or above, as well as people aged 50 to 74 who have risk factors for severe RSV disease.

For pregnant women, the main aim is to protect the baby after birth. The antibodies produced by the mother can cross the placenta and help protect the baby during the first six months of life, when the risk of severe RSV is greatest. Clinical trial data suggest that maternal vaccination can reduce the baby’s risk of RSV-related hospitalisation by about 68% during the first three months after birth. It can also substantially reduce the risk of severe outcomes. However, this protection gradually decreases over time.

If a pregnant woman does not receive a maternal RSV vaccine, doctors may offer a long-acting RSV antibody directly to the baby after birth. In general, most babies do not need both forms of protection. The best option depends on the expected delivery date, local RSV activity, the baby’s risk factors and medical advice.

Possible disadvantages and limitations

Common vaccine side effects include pain at the injection site, tiredness, headache, muscle or joint pain, nausea and a short-lived fever. These reactions are usually mild and temporary.

For some adult RSV vaccines, clinical studies and safety monitoring have identified a possible association with the very rare Guillain–Barré syndrome (GBS), a neurological condition that can cause muscle weakness. The estimated additional risk among adults aged 60 or above is around 10 extra cases per million vaccinated people. This safety information continues to be monitored and updated.

Pregnant women should also be aware that possible links with hypertensive disorders of pregnancy, including pre-eclampsia, and preterm birth continue to be monitored. Current evidence does not prove that the vaccine causes these problems, but the possibility has not been completely ruled out. Therefore, “safe” does not mean that the risk is zero. Vaccine protection also decreases over time, and vaccination does not necessarily need to be repeated every year. Cost and availability may affect the practical benefits as well.

Advice for pregnant women

Before deciding, pregnant women should discuss their medical history with an obstetrician or family doctor. Important information includes any history of severe allergic reactions, pregnancy-related hypertension, risk of preterm birth and other medical conditions. Anyone who has had a severe allergic reaction to a vaccine component should not receive that product.

The timing of vaccination depends on local recommendations. For example, United States guidance generally recommends maternal RSV vaccination between 32 and 36 weeks of pregnancy, while international guidance allows vaccination during the third trimester according to local policy. In Hong Kong, universal RSV vaccination is not currently recommended for all pregnant women. Instead, vaccination may be considered as an individual decision after discussing the potential benefits and remaining uncertainties with an obstetrician or family doctor.

During the discussion, consider the expected delivery date, local RSV activity, whether the baby has other risk factors, and whether a long-acting RSV antibody could be given after birth. Regardless of which option is chosen, family members should wash their hands regularly, keep anyone who is ill away from the newborn, avoid sharing towels or utensils, and maintain good indoor ventilation.

Seek medical attention promptly if a baby develops rapid or difficult breathing, bluish lips, feeding difficulties, noticeably fewer wet nappies or unusual sleepiness. This article is for health education only and does not replace personalised medical advice.