Influenza vaccine for pregnant women may be slower to deliver

Pregnant women have a slower response to the flu vaccine than healthy women because they may be not getting enough support from their doctors, according to a new study. Researchers from the Fred Hutchinson…

Influenza vaccine for pregnant women may be slower to deliver

Pregnant women have a slower response to the flu vaccine than healthy women because they may be not getting enough support from their doctors, according to a new study.

Researchers from the Fred Hutchinson Cancer Research Center in Seattle conducted the study, which has been published in the International Journal of Epidemiology.

Researchers looked at more than 100,000 women who were diagnosed with flu or flu-like illness during the 2014-2015 flu season. They found that for every one point increase in an annual or yearly total of HPAI scores (a calculation of the body’s ability to fight off the flu) of 38 weeks, pregnant women were 0.15 point lower in response to a shot.

A single dose of the shot containing both a weakened flu virus and one inactive strain will give a full 60 percent protection against the whole flu virus, researchers said.

“However, the protection for some years for most pregnant women was only about 60 percent, meaning they’d only get about half the protection they’d get if they received two doses,” said Dr. Joanna Zelman, lead author of the study.

The data was gathered from data submitted to the Centers for Disease Control and Prevention’s Northern Zone influenza surveillance program. Researchers found that pregnant women who had sickbed episodes or developed side effects were more likely to respond to a flu shot, which suggested the increased disease severity in this group might be influenced by their current medical history and a decrease in care at the time.

The lack of adequate care for prenatal care was greatest in Arizona, Arkansas, and Texas, where researchers noted that women were typically hospitalized or saw a doctor more often and had much lower rates of admitted influenza-like illness. A significant link was also found in North Carolina and Rhode Island.

“We know that the protective dose of influenza vaccine is different for pregnant women from non-pregnant women,” Zelman said. “Previous studies have shown that pregnant women get small doses of a normal flu vaccine in pill form, and non-pregnant women receive larger doses of the H1N1 vaccine in tablet form.”

For instance, women who took ibuprofen during pregnancy had a slower response to the H1N1 vaccine than did women who took aspirin, Zelman said.

Flu specialists said that the study’s findings demonstrate an important disparity between how the two groups of pregnant women are treated.

“Very often, HPAI is measured every month for any number of diseases,” said Dr. Deborah M. Masterson, medical director of the flu laboratory at Franciscan Health in Springfield, Mo. “It may take weeks for a pregnant woman to respond to any given medicine, and sometimes even longer. Often, if she’s had a mild illness in the last six months, then she may not be able to take the medicine as prescribed, especially if it’s a controlled substance. They’ll know she’s pregnant, and then they’re going to give her a different dose.”

Dr. Amesh Adalja, an infectious disease physician and a senior associate with the Johns Hopkins Center for Health Security, said that the study’s findings are “not something I can just walk away from”.

“For any treatment, or for any test, if there’s a delay in response, it affects the protection that you provide the patient,” Adalja said. “Pregnant women may not get to bed as quickly and not be as healthy in this early stage of pregnancy. That leads to worse outcomes and outcome issues for the mother.”

Symptoms of the flu usually subside with five to seven days after the onset of illness. However, by four weeks, it is common for flu patients to have a severe case of flu.

“This is another reason to talk to your physician about why you’re not getting the flu shot,” Adalja said. “If you aren’t getting the protection, it’s probably not because you don’t want to get the flu, it may just be because you have better access to the vaccine in the non-pregnant group.”

Follow Jennifer Gray on Twitter: @JenniferLGray

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