Pregnant Women Will Be Included in H1N1 Flu Vaccine Trials

As predicted, pregnant women are, indeed, on the government's list of the first folks to be vaccinated against the H1N1 "swine flu" virus. The panel of experts convened by the Centers for Disease Control and Prevention recommended yesterday that the new vaccine be provided first to pregnant women and adults with compromised immune systems, who face a greater risk of complications, and others, like children and health-care workers, who are at higher risk of becoming infected, says Anne Schuchat, director of the CDC's National Center for Immunization and Respiratory Diseases. Some 159 million people fall into these high-priority groups, and whether there will be enough vaccine for all of them when it first becomes available isn't known.

In the event that there are shortages, the panel also came up with a superhigh-priority list of those who should be vaccinated—some 41 million individuals. Once again, pregnant women are on this list. Just how many of them will rush out to get vaccinated, however, remains a mystery. Studies suggest that fewer than 15 percent of expectant moms currently get the seasonal flu vaccine, but more may be willing to get the H1N1 vaccine—and their doctors may push harder for them to have it—given the latest data showing that pregnant women infected with H1N1 are more likely to develop severe complications.

The trouble is, many pregnant women are extremely cautious about getting any shots or medicines because of the potentially harmful effects that these agents could have on a developing fetus. In fact, vaccines that contain live weakened viruses, like measles, aren't administered during pregnancy because of the possibility that they could cause a high fever in the woman—raising the risk of birth defects—or an infection in the fetus. The seasonal flu and H1N1 shots, however, contain dead viruses that don't pose either of these problems. Still, many experts agree, the H1N1 vaccine should be tested in pregnant women before it's licensed for use during pregnancy. (Studies have already established that seasonal flu vaccine is safe and effective to use at any stage of pregnancy.) 

The National Institutes of Health is set to begin testing the vaccine in pregnant women in the next month or two. "We're still awaiting word from our institutional review board [which signs off on all clinical trials], so we don't yet know who will be included," says Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, which is part of NIH. Although he says there's no reason not to include pregnant women at the earliest stage of pregnancy, the review board could "out of an abundance of caution" limit the trials to women who are beyond the first 12 weeks of pregnancy. Unfortunately, he adds, safety and efficacy data won't be available from those pregnant women trials when the vaccine initially becomes available in late October.

One question the trials may address is at what stage during pregnancy the vaccine should be given. Swine flu complications tend to be much worse when women get infected near the end of pregnancy as opposed to during the first 12 weeks. And there's always the possibility—no matter how remote—that something administered during those early weeks when a fetus's organs are still developing could cause birth defects. "This is a new vaccine, so we can't say whether it's safer to give during one period of pregnancy or another," says Mark Steinhoff, director of the global health center at Cincinnati Children's Hospital, who has researched the use of seasonal flu vaccine in pregnant women.

By and large, there's no reason to think that the H1N1 vaccine will pose any problems for pregnant women since it's being produced in exactly the same fashion as the seasonal flu vaccine. What's more, Steinhoff adds, pregnant women who get vaccinated will probably also confer antibody protection to their newborns who are too young to be vaccinated themselves. This could prove lifesaving if H1N1 infections become extremely widespread or the virus mutates into a deadlier strain.

Pregnant women are also advised to get Tamiflu if they experience symptoms of swine flu like high fever, sore throat, and a cough. But some experts are concerned over the lack of research on the use of this drug in pregnant women infected with H1N1. "We are hugely concerned that we don't know what the right dose is for pregnant women," says Ruth Faden, director of the Berman Institute of Bioethics at Johns Hopkins University. "While it may be that the standard dose of Tamiflu is perfectly appropriate, it's at least possible that it's an insufficient dose for pregnant women at a given stage in pregnancy." That's because pregnant women's kidneys clear drugs faster from the body, which means that certain drugs may not enter the bloodstream at therapeutic levels. (This has been demonstrated with some antibiotics, but Tamiflu hasn't been tested in pregnant women.) "I think the message we should be getting out is that pregnant women should be vaccinated," she says, and that those who get infected and treated with Tamiflu should be studied in clinical trials to see if the drug is given at an effective dose. "This is a tough situation. I wish we weren't in it."