Should pregnant women get the flu shot? What research tells us

Question: Should pregnant women get the flu shot?

The straight answer: yes

The facts: pregnant women are advised to stay clear of medications and vaccinations during their pregnancy. However, research findings show that the inactivated flu vaccine is beneficial to both mother and unborn baby, as it protects against infection during the first few months of life.

Despite the research in its favour, most women are still wary of the flu vaccine. Dr Alexander Kenneth Doo, specialist in obstetrics and gynaecology at The Women’s Clinic in Hong Kong, recommends it for every pregnant woman. Doo says: “Immunity is lowered during pregnancy and if infected, an expectant mother can be more severely affected than others, posing a risk to herself and the baby. There is also evidence that taking the vaccine can have a protective effect as the immunity is passed onto the baby.”

Flu is an infectious disease caused by various forms of flu virus. The most common strains in Hong Kong are the H1N1 and H3N2 variants of influenza A, and influenza B. While it occurs throughout the year, it’s more prevalent between January and March and July and August in Hong Kong. The virus mainly spreads through respiratory droplets and is characterised by fever, sore throat, cough, headache, muscle aches, runny nose and general tiredness.

According to the WHO, an inactivated seasonal influenza vaccine is safe during pregnancy and there is no evidence showing that it causes abnormal foetal development even when administered during the first trimester.

However, Doo cautions that patients with severe egg allergies should only be given the vaccine in settings where their response can be monitored and appropriate remedial action taken.

The nasal vaccine should be avoided, as it contains a live virus that could cause an infection with complications in people with weakened immune systems or other underlying medical conditions.

The side effects experienced by pregnant women are the same as those experienced by other people. They are generally mild and include soreness, redness, and/or swelling around the injection site, fainting, headache, fever, muscle aches, nausea and fatigue. But these generally last for just a day or two.

Despite the benefits of the flu vaccine, its use by pregnant women is quite low.

Susanna Esposito, a professor of paediatrics at the University of Milan in Italy who leads the European Society of Clinical Microbiology and Infectious Diseases Study Group for Vaccines, highlights some of the benefits of the flu vaccine: she says the inactivated flu vaccine is safe for pregnant women and does not harm the fetus. It protects the mother against flu for the season she is pregnant, making it less likely she will develop flu-related complications.

The inactivated vaccine itself does not pass into the blood system of the fetus. The antibodies that develop in the mother’s blood pass through the placenta, thereby conferring secondary immunity that lasts for the first few months of life.

According to Hong Kong’s Centre for Health Protection, flu vaccination in pregnant women has shown benefits for both mother and child in terms of reduced acute respiratory infections. The benefits of the vaccination to a baby through its mother is especially important, since so far no flu vaccine has been approved for use with infants under six months old.

Babies aged up to five months are five times more likely to require a hospital visit due to flu than children aged six to 23 months. Mortality rates are also the highest in this age group, with 0.88 deaths per 100,000 children infected.

As many as 30 per cent of children are infected with the flu virus every season. “The impact of the infection is greatest in children younger than six months, 228,000 of whom require treatment in hospital every year worldwide,” says Esposito.