Protecting Pregnant Patients (and Their Babies): The Importance of Influenza Vaccinations
Protecting Pregnant Patients (and Their Babies): The Importance of Influenza Vaccinations
By Jeffrey T. Jensen, MD, MPH, Editor, Leon Speroff Professor of Obstetrics and Gynecology, Vice Chair for Research, Oregon Health and Science University, Portland, is Editor for OB/GYN Clinical Alert.
Synopsis: The 2009 Influenza A (H1N1) vaccine is safe and effective, and induced a typically protective immune response in the majority of subjects between 12 and 60 years of age. Lesser immune responses were seen after a single dose of vaccine in younger and older subjects, but a second shot increased response in both of these groups.
Source: Zhu FC, et al. A novel influenza A (H1N1) vaccine in various age groups. N Engl J Med 2009 Oct 21; Epub ahead of print; available at www.nejm.org.
A 2009 influenza a (h1n1) vaccine was evaluated in a large randomized placebo controlled study in China. The immunization schedule consisted of two doses administered 21 days apart. A total of 2200 subjects received one dose, and 2103 (95.6%) received a second dose of either the vaccine or placebo. Importantly, the authors reported no severe adverse side effects associated with the vaccine. Mild injection site or systemic symptoms were noted in 5.5%-15.9% of subjects. By day 21, protective antibody titers against the virus were seen in 97.1% of subjects between 12 and 60 years of age, but only 74.5% among children ages 3-11 years and 79.1% of adults age 61 years and older. By day 35, a protective titer had been achieved in 98.1% of children ages 3-11 and 93.3% of those age 60 and older. There was no significant difference in response between the 15 and 30 µg doses of vaccine.
The influenza A (H1N1) pandemic is in the news every day. The good news is that the virus is far less virulent than originally predicted. The bad news is that this is still a very bad flu, and that pregnant women represent a particularly vulnerable population. That said, pregnant women always represent a vulnerable population for any influenza; this is the reason why efforts to immunize pregnant women every year for seasonal flu are so important.
So why is this flu season different? Every year, world health leaders must make a guess as to what flu strains to select for the seasonal flu vaccine. Influenza viruses are selected based on forecasts (based on active surveillance gathered by 122 national influenza centers in 94 countries) about what viruses are most likely to cause illness in the coming season.1 Therefore, each year's seasonal flu vaccine is designed to protect against the seasonal influenza viruses expected to cause disease during that influenza season. The seasonal influenza vaccine contains three influenza virus strains; one influenza A (H3N2) virus, one regular seasonal influenza A (H1N1) virus, and one influenza B virus. Every winter, the WHO recommends the specific virus strains for a Northern Hemisphere vaccine for the coming flu season, and in the United States, an advisory committee convened by the FDA makes the final decision about vaccine strains in February. Manufacturers grow vaccine strains based on these recommendations as early as January to get a head start on the lengthy manufacturing and quality control process.
Unfortunately, this year, the H1N1 strain selected for the seasonal vaccine was wrong. This serious and novel H1N1 strain was identified in early spring — at the time production for the seasonal vaccine was already in progress. Had this H1N1 strain been recognized late last year, it would have been a part of this year's routine seasonal vaccine. Since it was not, health authorities needed to scramble to formulate, manufacture, test, and distribute a second flu vaccine for this year. To compound the problem, the yield of viral particles (grown in chicken eggs) used to produce the vaccine has been lower than expected, contributing to an initial supply shortage.
Since we recognize that pregnant women (and their newborns and infants) will suffer disproportionately from illness and death from influenza, the best strategy to prevent this is to vaccinate pregnant women for both 2009 H1N1 influenza and seasonal flu. The situation with two vaccines this year greatly complicates matters as some women and providers will believe they are protected against H1N1 after receiving the seasonal flu vaccine, and against the other predicted seasonal influenza strains after the H1N1 vaccine. The late availability and short supply (explained above) contribute to public confusion. Unfounded concerns and speculations about safety and efficacy circulated and reinforced by news media have fanned the fire. That is why the additional safety information provided by the Chinese study is significant. A total of 2200 subjects ages 3-77 received at least one dose of the vaccine with no serious vaccine-related adverse events. Although some younger children and older adults appear to require two injections for full protection, the important action for clinicians today is to make sure that all pregnant women receive a seasonal flu vaccine now, and an H1N1 vaccine as soon as it becomes available. The CDC and state and local public health authorities are triaging H1N1 vaccine to make it available to pregnant women first.
Concerns that thimerosal (a mercury preservative in the multi-dose vaccine) could be harmful to a pregnant woman or to her fetus limit uptake of vaccination by some groups. While the most current research does not support a link to thimerosal and neuropsychological impairment in children,2 emotion often speaks louder than evidence when risks in pregnancy are concerned. Therefore, you should make sure that your patients know that a single-dose H1N1 vaccine that does not contain thimerosal is available. Reassure your patients that while H1N1 vaccine is new it has been made and tested the same way as the seasonal flu vaccines that millions of pregnant women have received for more than 45 years. Flu vaccine has not been shown to cause harm to pregnant women or their babies. Guillain-Barré (GB) syndrome is extremely rare, and the association with vaccination is currently in question. Still, a history of GB syndrome, any prior severe vaccine-related illness, or allergy to chicken eggs represents the rare contraindications to the flu vaccination.
Another strong selling point to pregnant women is that obtaining a flu vaccine actually protects their newborn and infants (thanks to OB/GYN Clinical Alerts reader Evan F. Evans, MD, for emphasizing this point in a recent letter). Newborns rely on passive transfer of immunity from their mothers, since they cannot develop active immune response until after age 6 months. A randomized controlled trial published by Zaman in 2008 in the New England Journal of Medicine found that inactivated influenza vaccine given to pregnant women reduced proven influenza illness by 63% in infants up to 6 months of age and averted approximately one-third of all febrile respiratory illnesses in mothers and young infants.
I strongly urge you to vaccinate your pregnant, postpartum, and breastfeeding patients (and other family members that might have contact with newborns and infants) for both seasonal flu and H1N1. Although a nasal spray vaccine is available, this contains live virus and should not be used in pregnant women. Postpartum and breastfeeding women can receive either the flu shot or the nasal spray. The H1N1 and seasonal flu vaccinations can be administered at the same time but in different injection sites, and can be given at any time during pregnancy. Children older than 6 months, but younger than 12 years, and family contacts older than age 60 should receive two doses of vaccine.
You should also familiarize yourself with the guidelines for triage and treatment of pregnant women who develop an influenza-like illness. The CDC maintains regularly updated information for health care providers on their web sites (go to www.cdc.gov/H1N1flu/pregnancy/antiviral_pregnant_qa.htm for information on treatment and www.cdc.gov/h1n1flu/diagnostic_testing_clinicians_qa.htm for information on diagnostic tests). There is no need to confirm a diagnosis before treatment, and in many cases you may chose to treat a stable pregnant patient over the phone rather than have her come into the office or labor and delivery. The American Congress of Obstetricians and Gynecologists also has developed new materials for triage and counseling that can be printed from their web site at www.acog.org/departments.
- Centers for Disease Control and Prevention. Seasonal Influenza (Flu): Selecting the Viruses in the Seasonal Influenza (Flu) Vaccine. Available at: www.cdc.gov/flu/professionals/vaccination/virusqa.htm. Accessed Oct. 25, 2009.
- Thompson WW, et al. Early thimerosal exposure and neuropsychological outcomes at 7 to 10 years. N Engl J Med 2007;357:1281-1292.
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