Flu Vaccine in Pregnancy

This deserves a plain answer, because it is the single most common reason women hesitate. The injected flu vaccines used in the UK contain no live viruses at all — only killed virus or fragments of it, enough for your immune system to learn from but incapable of causing infection. The NHS states it without qualification: injected flu vaccines do not contain any live viruses and cannot cause flu.

The myth persists for understandable reasons. A sore arm and a day of mild temperature afterwards is your immune system responding — not flu, which is a far heavier illness. And vaccination happens in autumn, just as colds, RSV and COVID begin circulating: catching one the week after your jab is coincidence, not cause.

Babies under six months are among those most at risk of serious illness from flu, and no flu vaccine is licensed for them. The only way to protect a newborn is through their mother: your antibodies cross the placenta and cover your baby for the first few months of life — precisely their most vulnerable window.

That benefit has been measured in randomised trials. In a trial of 340 mothers in Bangladesh, vaccination in pregnancy cut laboratory-confirmed flu in babies under six months by 63% (95% CI 5–85), and febrile respiratory illness in the mothers by 36% (Zaman et al., NEJM 2008).

In a placebo-controlled trial of 2,116 pregnant women in South Africa, efficacy against PCR-confirmed flu was 50.4% (95% CI 14.5–71.2) in mothers and 48.8% (95% CI 11.6–70.4) in their infants (Madhi et al., NEJM 2014).

Across almost 20,000 pregnant women over six seasons, vaccination was also roughly 40% effective at preventing flu hospitalisation in pregnancy (Vaccine Knowledge Project).

The same before-birth logic underpins the whooping cough and RSV vaccines, which protect your newborn the same way.

Inactivated flu vaccines have been given in pregnancy for decades, and every pregnant woman in the UK has been offered one routinely since 2010. The scale of use is easy to underestimate: in England alone, an estimated 228,054 pregnant women were vaccinated in the 2024/25 season (35.0% uptake — UKHSA), and uptake has run at roughly a third of pregnancies each season since 2010.

That scale means safety has been studied, not assumed. A 2017 US study compared over 52,000 babies exposed to the flu vaccine in the first three months of pregnancy with over 370,000 who were not, and found no increased risk of birth defects. The review cited in UKHSA's Green Book concluded the inactivated vaccine can be safely given in any trimester.

The associations actually found run the other way: vaccinated women are less likely to deliver prematurely, to have a low-birth-weight baby, and in several studies less likely to experience stillbirth. What has not been found is any credible link to miscarriage, birth defects or harm to the developing baby.

One practical note: some UK flu vaccines are grown in hens' eggs and contain trace ovalbumin. Most people with egg allergy can still be vaccinated, and egg-free alternatives exist — tell us about any allergy when you book. Serious allergic reactions are very rare, and every clinician who vaccinates is trained and equipped for them.