Daniel M. Keller, PhD

October 28, 2010

October 28, 2010 (Vancouver, British Columbia) — Last year's H1N1 influenza vaccine was safe for pregnant women and was well tolerated. There was no difference in reported adverse effects between unvaccinated women and women who received the H1N1 vaccine alone or with the seasonal influenza vaccine, except for arm soreness.

Stephanie Irving, MHS, epidemiologist at the Marshfield Clinic Research Foundation in Wisconsin, reported the results of this survey of pregnant women who did or did not plan to be vaccinated here at the Infectious Diseases Society of America (IDSA) 48th Annual Meeting.

Reported rates of hospitalization and death for pregnant women were higher than in the general population during the 2009 H1N1 pandemic. The United States Advisory Committee on Immunization Practices made pregnant women a high priority for H1N1 vaccination. In prelicensure trials, the H1N1 vaccine appeared to be as safe as the seasonal influenza vaccine. Targeting common acute adverse effects, the investigators set out to describe the postlicensure safety profile of the H1N1 vaccine.

They recruited pregnant women 18 years or older (n = 767; gestation of less than 38 weeks) from the Marshfield Clinic and from Kaiser Permanente Northwest in Portland, Oregon, who had not received the vaccine more than 24 hours before enrollment. The women filled out a 14-day symptom and temperature diary.

The mean maternal age at enrollment was 28 years, 26% were covered by Medicaid or public insurance, and the mean gestational age at enrollment was 18 weeks (range, 4 to 38 weeks). Of the 767 women, 68% received no vaccination, 25% received the H1N1 vaccine only, 6% received the H1N1 and seasonal vaccines, and 1% received only the seasonal vaccine. About 36% received the H1N1 vaccine in the first trimester (either alone or with the seasonal vaccine), 28% in the second trimester, and 24% in the third trimester.

Complete symptom data were available for 571 women. The most frequently reported symptom on at least 1 day of the reporting period was headache, reported by approximately 63% and 43% of participants at the Marshfield Clinic and Kaiser Permanente Northwest sites, respectively, followed by nausea (49% and 38%), muscle ache (about 30%), arm soreness (about 25%), chills (about 20% at both sites), and diarrhea (about 10% at both sites). A few participants reported rash.

For all symptoms except arm soreness, the women who received either the H1N1 vaccine alone or with the seasonal vaccine did not differ from unvaccinated women in reporting a symptom on at least 1 day of the reporting period. About 64% of women who received the H1N1 vaccine alone had arm soreness, as did 71% of women who received both vaccines; only about 2% of unvaccinated women did.

Among the 20% of women who reported headaches, the majority were mild, with only about 12% to 18% of them rated as moderate or severe. The headache reports did not differ between vaccinated and unvaccinated women. Similarly, only about 20% of women reported nausea, mostly mild, and the prevalence of nausea did not differ from the unvaccinated cohort. Only about 10% reported muscle aches, which were generally mild and did not differ from unvaccinated women. Arm soreness was virtually absent among the unvaccinated women and was generally mild among vaccinated women who reported it. Virtually all participants were afebrile, and the vaccinated groups did not differ from each other or from the unvaccinated group.

Limitations of the study were that it depended on unverified self-reported data, that the participants subjectively assessed symptom presence and severity, and that the unblinded reporting was subject to potential bias. Also, the reporting period was limited to 14 days, the study did not examine uncommon adverse events, and because the population was enrolled in managed care, it might not be representative of the general American population.

Ms. Irving said that a study is underway to look at vaccination status and pregnancy complications and fetal outcomes. Also, the current study is being replicated to examine the safety of the 2010 seasonal vaccine in pregnant women.

She concluded that "the study of 767 pregnant women did not find any serious short-term complications after H1N1 influenza vaccination. . . . Reported side effects of the vaccine were minimal. Women who received the vaccine were not more likely to report any of the side effects for which we monitored [than] unvaccinated women, except for arm soreness, as expected."

Andrew Pavia, MD, chair of the Pandemic Influenza Task Force for IDSA and chief of the Division of Pediatric Infectious Diseases at the University of Utah in Salt Lake City, noted that pregnant women are "wisely suspicious" of drugs in general, so it is a complicated message to them about influenza vaccine. Flu vaccines have previously been shown to be safe during pregnancy; there was a question about the 2009 H1N1 vaccine only because it had not been evaluated extensively.

"This additional information that, again, this vaccine, like other flu vaccines, was as safe in pregnant women as in nonpregnant people was very helpful," he explained. Finally, he said, after several years of low vaccination rates among pregnant women, more of them have been getting the flu vaccine, probably because obstetricians have been advocating it.

Dr. Pavia said that all influenza can be particularly high risk for the mother (e.g., because of pneumonia and heart problems) and for the baby during pregnancy and delivery. An added benefit, he said, is that vaccination of the mother can protect the baby from flu for up to the first 6 months of life.

In another presentation at IDSA, Marci Drees, MD, MS, from the Department of Medicine at Christiana Care Health System in Wilmington, Delaware, and Jefferson Medical College of Thomas Jefferson University in Philadelphia, Pennsylvania, presented the findings of her study on factors affecting the acceptance of H1N1 vaccine by pregnant women. This group has had one of the lowest uptake rates of flu vaccination among all high-priority groups, and they had a disproportionately high mortality rate from the 2009 H1N1 virus.

Dr. Drees and colleagues administered a 12-question survey to new mothers on postpartum day 1 or 2 at their 900-bed community-based academic medical center between February 1 and April 15, 2010. Among 307 women, 62% had been vaccinated against the H1N1 virus, and 32% had been offered the vaccine but had refused.

In a multivariate analysis, a doctor's recommendation was one of the strongest predictors of acceptance of H1N1 vaccination (odds ratio [OR], 6.9; 95% confidence interval [CI], 2.7 - 17.6). If the woman had received the seasonal flu vaccine while pregnant, she was more likely to receive the H1N1 vaccine as well (OR, 4.4; 95% CI, 2.4 - 8.1). In addition, some or all family members or caregivers being vaccinated against H1N1 predicted the H1N1 vaccination of the pregnant woman (OR, 2.8; 95% CI, 1.5 - 5.3). Non-Hispanic black women were 70% less likely to be vaccinated against H1N1 (OR, 0.3; 95% CI, 0.2 - 0.7; < .001 for all).

Among women choosing not to be vaccinated, safety concerns were the primary barrier. Many unvaccinated women reported that they were not aware that they were at increased risk from the H1N1 flu.

The investigators emphasized the role of physicians in recommending vaccination and the need for continued engagement with obstetrical providers to reinforce this message and to sustain high vaccination rates among pregnant women. "Our study shows that if obstetrical providers and public health authorities really make a concerted effort to vaccinate pregnant women for flu and educate them about the risks and benefits, they are willing to be vaccinated even in a setting where the vaccine is often perceived as more risky than the usual seasonal flu vaccine," Dr. Drees said.

Dr. Pavia said that because of the H1N1 virus, rates of immunization have gone up, primarily because of efforts by pregnancy care providers. "The biggest predictor of not getting vaccinated has to do more with access to care . . . and how the vaccine was presented to them as an option," he said.

The study was funded through a subcontract with America's Health Insurance Plans from the Centers for Disease Control and Prevention. Ms. Irving, Dr. Drees, and Dr. Pavia have disclosed no relevant financial relationships.

Infectious Diseases Society of America (IDSA) 48th Annual Meeting: Abstracts 871 and 1346. Presented October 23, 2010.


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