Better timing with flu vaccination campaigns could protect more pregnant women, babies

November 03, 2021

2 min read


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A study in Brazil suggested that vaccinating women earlier in the influenza season could improve birth outcomes.

Expectant mothers who had not been vaccinated against influenza and were infected had higher rates of complications, the researchers said, putting their babies at risk during birth and later in life.

Seasonal influenza already was circulating in the weeks and months before the rollout of national influenza immunization campaigns in the semiarid state of Ceará, the researchers said. Influenza circulation begins there as early as mid-March and peaks 2 to 3 months earlier than in the south and southeast of the country, yet all of Brazil sticks to the same vaccination schedule.

“This misalignment was associated with seasonal patterns of premature birth, low birth weight and birth by cesarean,” Sean R. Moore, MD, a pediatric gastroenterologist at the University of Virginia Children’s Hospital, said in a university press release.

The observational descriptive study included children born to mothers with severe acute respiratory infections (SARI) during pregnancy (n = 61) and a control group of randomly selected mothers who did not have SARI during pregnancy (n = 122) in Ceará from 2013 to 2018.

The researchers found that 30 to 40 weeks after the peak of influenza season, the average birth weight fell by 40 g and premature birth rates increased from 10.7% to 15.5%.

Also, the 61 babies born to mothers with SARI had significantly lower birth weights (P = .02), were more likely to be premature (P = .03), experienced shorter gestation times (P < .01) and had lower Apgar scores 5 minutes after birth (P < .01) than the 122 children in the control group.

These trends repeated year after year, the researchers said. H1N1 was the predominant subtype during almost all the seasonal outbreaks between 2013 and 2018.

Children exposed to influenza and other infections in the womb are at significantly greater risk for neurocognitive, physical and educational problems later in life, according to the researchers, who concluded that earlier influenza vaccination campaigns in Brazil would better protect pregnant women and their babies.

Brazil’s influenza season typically begins in Ceará, the researchers continued, so improving the timing of vaccination campaigns there ultimately could benefit the entire country.

Sean R. Moore

“Brazil is a country with enviably high influenza vaccine uptake — greater than 80% in people at high risk for severe influenza. Our data suggest giving vaccines earlier in the year in Ceará would better protect women during pregnancy and reduce bad outcomes,” said Moore.

Currently, influenza vaccines are not recommended for infants aged younger than 6 months.

“When a mother chooses to receive the flu vaccine during pregnancy, she is giving an early gift to her baby,” Moore said. “Mom’s vaccine-acquired antibodies are shared with her fetus and persist to help protect her baby against influenza during the vulnerable first months of life.”

The researchers said their findings could improve lives in Brazil and send a message about the importance of timely vaccination to the rest of the world.

“This study confirms the importance of the flu vaccine for pregnant mothers,” Daniel Roshan, MD, FACOG, FACS, of NYU Langone Health, who was not involved in the study, told Healio.

Daniel Roshan

“Of course, timing of the vaccine is important, and it should be given prior to peak flu season,” Roshan continued, adding that current U.S. recommendations say it should be given in the fall and as soon as possible.

“I think the timing of early fall is good and does not need to change,” he said. “All pregnant women should be aware of the risk of flu in pregnancy and receive the vaccine.”


Filho JQ, et al. Emerg Infect Dis. 2021;doi:10.3201/eid2709.203791.


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Jane Frederick, MD, FACOG)

Jane Frederick, MD, FACOG

This interesting study has some critical implications for how we administer the flu vaccine. Pregnant women are at very high risk for sickness related to the flu. When you’re pregnant, your lung capacity is lower, your immune system changes and you’re susceptible to all respiratory viruses. Flu vaccinations should be a priority for women who are pregnant or planning to become pregnant.

When the mother’s breathing is compromised, the baby also is compromised because they depend on mom’s oxygenation for their health and ability to grow. This study showed that there are issues with low birth weight and preterm birth, and other studies have shown that influenza vaccines are safe during pregnancy. These vaccines protect infants under 6 months of age from infections as well.

Patient awareness is important. Doctors really need to spread the word that patients who are pregnant or planning to become pregnant are a priority group for vaccination. We should recognize that these patients are different and at high risk for influenza and try to do more to reach them.

When your patient is at the pharmacy and she’s picking up her kids’ cough medicine, that may be a good time for the pharmacist to ask, “Have you been vaccinated for the flu? Are you in this high-risk category?” That might be one area where we could invest in promoting knowledge.

People have heard a lot of myths about the flu vaccine. We have to dispel those myths and present the science of why pregnant patients are at high risk. Even in my own practice, pregnant patients do not know how much more risk they are at for respiratory viruses.

Pregnant patients also have the mindset that they shouldn’t add anything different to their body. They don’t smoke. They don’t drink alcohol. They make sure their food intake is perfect. When I say I’m going to give them a vaccine, they push back.

I have had a lot of difficulty convincing my patients to get vaccinated. But once I talk about the science, they become more receptive because it’s coming from me – the specialist, the physician. They know I have their best interest at heart. After I explain the science, most patients are very amenable to getting vaccinated.

I want to educate pregnant patients about how they are more highly susceptible to respiratory viruses, especially the flu. I think OB/GYNs are intensely promoting these risks. It would be great to get more primary care practitioners to tell their patients that it’s okay to get vaccinated too.

Jane Frederick, MD, FACOG

Medical director, HRC Fertility

Disclosures: Frederick reports no relevant financial disclosures.


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