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Content on this page was developed during the 2009-2010 H1N1 pandemic and has not been updated.

  • The H1N1 virus that caused that pandemic is now a regular human flu virus and continues to circulate seasonally worldwide.
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2009 H1N1 Influenza Vaccine and Pregnant Women: Information for Healthcare Providers

January 14, 2010, 3:00 PM ET


The purpose of this document is to provide information for healthcare providers on 2009 H1N1 monovalent influenza vaccination and pregnant women. Additional information about the 2009 H1N1 monovalent vaccine is available.


Some pregnant women who have been infected with the 2009 H1N1 virus have had severe illness. Overall, pregnant women have had higher rates of hospitalization than the general population. About 6% of confirmed H1N1 2009 influenza deaths in the U.S. have been in pregnant women, while only about 1% of the general population is pregnant at any given time. One recent large case control study* found that the seasonal flu shot (inactivated flu vaccine) given to pregnant women reduced flu illness in their infants under 6 months of age by 63%, confirming that seasonal flu vaccination of pregnant women can benefit both mothers and infants. The Advisory Committee on Immunization Practices (ACIP) designated pregnant women as one of the initial target groups to receive the 2009 H1N1 monovalent vaccine as soon as it is available. Clinical trials evaluating the vaccine in pregnant women are underway by the National Institute of Allergy and Infectious Diseases (NIAID). Additional information about these trials are available.

What supply and distribution information is available to providers for the 2009 H1N1 monovalent flu vaccine?

Visit "H1N1 Clinicians Questions and Answers" for supply and distribution information, including flow of vaccine from manufacturers to providers, how to become a provider, and how to obtain vaccine. Also, please visit "2009 H1N1 Influenza Vaccine Supply Status" for the daily vaccine supply numbers.

How should healthcare providers organize their clinics for vaccination?

One of the most important actions providers of obstetrical care can take is to strongly recommend to their patients that they receive vaccine. Provider recommendation has repeatedly been shown to be a key predictor of acceptance of influenza vaccination.

Providers who care for pregnant women are in an ideal position to provide 2009 H1N1 monovalent influenza vaccine given the frequency of visits during pregnancy. There are many ways that clinics and offices can support vaccination of their pregnant patients. Some suggestions include vaccinating patients at the time of their prenatal visit or offering separate vaccination days or clinics when all well pregnant patients can receive vaccine. Offering vaccine during regular clinic visits should occur even in practices with separate vaccination days or clinics, in order to reach pregnant women who may not take advantage of those opportunities.

Practices that do not choose to stock and provide H1N1 monovalent vaccine should identify locations for referral of patients for vaccination.

Options for referral include:

  • Partnering with other offices in the geographic region and designating one site for vaccination
  • Partnering with local hospitals or birthing centers where patients deliver
  • Providing information to patients about local vaccination clinics

How many vaccine doses will a pregnant woman need to get?

The U.S. Food and Drug Administration (FDA) has approved the use of one dose of vaccine for full protection for persons 10 years and older. Therefore, a pregnant woman is recommended to get one dose of the 2009 H1N1 monovalent vaccine.

If a pregnant woman delivers her baby before receiving her seasonal flu shot or her 2009 H1N1 flu shot, should she still receive them?

Yes. In addition to protecting her from infection, the vaccine may also help protect her young infant. Flu vaccines are recommended only for infants 6 months or older. It is recommended that everyone who lives with or provides care for an infant less than 6 months old receive both the seasonal flu vaccine and the 2009 H1N1 monovalent flu vaccine.

For planned pregnancies, how long should a woman wait after receiving nasal spray flu vaccines before becoming pregnant?

There are no studies of live attenuated influenza vaccine among women who are pregnant or who are planning to become pregnant. However, the vaccine virus is cold-adapted and replicates in the nasopharyngeal tissues rather than at core body temperature. Consequently, infection of a fetus with live attenuated influenza virus is very unlikely. It is not necessary to defer pregnancy for a specific interval following receipt of live attenuated influenza vaccine.

Can a woman who is breastfeeding receive the vaccine?

Yes. Both seasonal flu and 2009 H1N1 monovalent influenza vaccines should be given to breastfeeding mothers. Breastfeeding is fully compatible with flu vaccination, and preventing maternal infection provides secondary protection to the infant. Maternal vaccination is especially important for infants less than 6 months old, who are ineligible for vaccination. In addition, transfer of vaccination-related antibodies by breastfeeding further reduces the infant’s chances of getting sick with the flu. While pregnant women should just receive the inactivated injectable form of influenza vaccine, nursing mothers can receive either the injectable or nasal spray form.

Is the 2009 H1N1 monovalent flu vaccine safe for pregnant women?

Flu vaccines have not been shown to cause harm to a pregnant woman or her baby. The seasonal flu shot has been recommended for pregnant women for many years. The 2009 H1N1 monovalent flu vaccine will be made using the same processes as the seasonal flu vaccine, and clinical trials of H1N1 monovalent vaccine safety in non-pregnant children and adults found results similar to those seen in studies of seasonal flu vaccine. Studies that test the 2009 H1N1 monovalent flu vaccine in pregnant women began in September. More information is available at "Clinical Trials of 2009 H1N1 Influenza Vaccines Conducted by the NIAID-Supported Vaccine and Treatment Evaluation Units".

Does the 2009 H1N1 monovalent flu vaccine have preservative in it?

Multi-dose vials of flu vaccine contain the preservative thimerosal to prevent bacterial growth. There is no evidence that thimerosal is harmful to a pregnant woman or a fetus. However, because some women are concerned about exposure to preservatives during pregnancy, manufacturers are producing preservative-free seasonal flu vaccine and 2009 H1N1 monovalent flu vaccine in single dose syringes. CDC recommends that pregnant women receive flu vaccine with or without thimerosal.

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Does the 2009 H1N1 monovalent flu vaccine have an adjuvant or squalene in it?

Adjuvants are agents that are sometimes added to a vaccine to increase its effectiveness. There are no adjuvants (such as squalene) in either the 2009 H1N1 monovalent or seasonal flu vaccines used in the United States.

Can the 2009 H1N1 monovalent flu vaccine be given at any time during pregnancy?

Seasonal flu vaccine is recommended for all pregnant women at any time during pregnancy, and has not been shown to cause harm to a pregnant woman or her baby. The Advisory Committee on Immunization Practices also recommends that 2009 H1N1 monovalent flu vaccine be given to all pregnant women at any time during pregnancy.

Will the seasonal flu vaccine also protect against the 2009 H1N1 flu?

The seasonal flu vaccine is not expected to protect against the 2009 H1N1 flu. Similarly, the 2009 H1N1 monovalent flu vaccine will not protect against seasonal flu.

Can the seasonal flu vaccine and the 2009 H1N1 monovalent flu vaccine be given at the same time?

Inactivated seasonal flu and 2009 H1N1 monovalent vaccines may be administered on the same day, but given at different sites (e.g., one shot in the left arm and the other shot in the right arm). If a woman is receiving her vaccines after delivery or after fetal loss, she can receive the nasal spray flu vaccine (live attenuated vaccine). However, coadministration of two live influenza vaccines on the same day is not recommended; they should be separated by at least 4 weeks.

Can pregnant women receive the nasal spray vaccine?

The nasal spray vaccine is not licensed for use by pregnant women. Pregnant women should not receive nasal spray vaccine for either seasonal flu or 2009 H1N1 flu. After delivery, women can receive the nasal spray vaccine, even if they are breastfeeding.

What are the possible side effects of the 2009 H1N1 monovalent flu vaccine?

Pregnant women are not known to have an increased risk of side effects from the flu vaccine. The side effects from 2009 H1N1 monovalent flu vaccine are expected to be similar to those from seasonal flu vaccines. The most common side effects following vaccination are expected to be mild, such as soreness, redness, tenderness, or swelling where the shot was given. Some people might experience headache, muscle aches, fever, fatigue, and nausea. If these problems occur, they usually begin soon after the shot is given and may last as long as 1-2 days. Fainting may occur shortly after receiving any injection and has uncommonly been reported after the flu shot. Like any medicines, vaccines can cause serious problems like severe allergic reactions. However, life-threatening allergic reactions to vaccines are very rare.

Anyone who has a severe (life-threatening) allergy to eggs or to any other substance in the vaccine should not get the vaccine, regardless of whether they are pregnant. Providers should ask patients whether they have any severe allergies or if they have ever had a severe allergic reaction following flu vaccination.

Is the 2009 H1N1 flu vaccine expected to be associated with Guillain-Barre Syndrome (GBS)?

During the 1976 Swine Flu vaccination program in the U.S., using a vaccine virus very different than the 2009 H1N1 virus, the 1976 vaccine was associated with cases of a severe paralytic illness called Guillain-Barre Syndrome (GBS). Approximately 1 additional case of GBS per 100,000 persons vaccinated occurred with the 1976 swine flu vaccine. Most studies done on seasonal flu vaccines after the 1976 vaccine showed no increased risk of GBS. However, two studies did demonstrate a small risk of approximately 1 additional case of GBS per 1 million persons vaccinated.

GBS occurs at a rate of 10---20 cases per 1 million adults, per year, regardless of vaccination. Substantial evidence exists that multiple infectious illnesses, most notably Campylobacter jejuni gastrointestinal infections and upper respiratory tract infections, including respiratory illness caused by influenza, are associated with GBS.

In general, seasonal flu vaccine has not been found to increase the risk for GBS. If a risk exists, it is low (i.e., approximately one additional case per 1 million persons vaccinated). The potential benefits of flu vaccination in preventing serious illness, hospitalization, and death substantially outweigh this estimate of risk for flu vaccine-associated GBS. Persons who have previously had GBS should not receive influenza vaccine.

What can providers do if there is a clinical adverse event following vaccine administration?

The Vaccine Adverse Event Reporting System (VAERS) is a US vaccine safety surveillance system, co-managed by CDC and FDA.

Clinically significant adverse events that follow vaccination should be reported to VAERS. Reports may be filed securely online, by mail, or by fax. Report forms are available online or can be obtained by calling 1-800-822-7967 to request reporting forms or other assistance.

What if a pregnant woman receives the live attenuated influenza vaccine?

Live attenuated influenza vaccines (seasonal or H1N1 LAIV) have not been studied in pregnant women and LAIV is not recommended for pregnant women. The inactivated influenza vaccines (seasonal and 2009 monovalent H1N1) are recommended for pregnant women. However, if a pregnant woman receives LAIV, for example, before she knows she is pregnant, she would not be expected to have any additional risks, compared with women who are not pregnant. The influenza vaccine virus replicates in the nose where body temperature is lower and has never been shown to replicate in other parts of the body or be passed to the unborn baby.

There are not any special measures to be taken if a pregnant woman has received live vaccine, i.e., revaccination with inactivated vaccine, taking antivirals, or enhanced testing. She should have pregnancy monitoring and testing as clinically indicated.

CDC and FDA are requesting that these instances of using LAIV in pregnant women be reported to the Vaccine Adverse Event Reporting System (VAERS). This will allow us to track these instances, even if there is no adverse event following the incident. Information for how to report to VAERS can be found above.

* Zaman K, Roy E, Arifeen S, et al. Effectiveness of maternal influenza immunization in mothers and infants. NEJM 2008;359:1555-64

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