The W.H.O. advises those who become infected to begin treatment as soon as possible.
This is the VOA Special English Health Report.
The H1N1 flu virus that has spread around the world is especially risky for pregnant women. If they become infected, especially after the first three months of pregnancy, they can get very sick or even die. Cases of fetal death have also been reported.
Pregnant women face an increased risk even during outbreaks of seasonal influenza. But the new H1N1 flu has been affecting a younger age group than seasonal flu epidemics.
The W.H.O. says pregnant women should take the antiviral drug Tamiflu as soon as possible after they show signs of illness. The drug is also called oseltamivir.
The agency says treatment should begin immediately and not wait for the results of laboratory tests. The effect are greatest when given within 48 hours. But experts say the medicine could still do some good even if there is a delay.
Since April, more than 1000 deaths have been reported from the H1N1 virus, commonly called swine flu. But so far the virus has not shown itself to be more severe than seasonal flu.
The World Health Organization has predicted that the H1N1 virus will infect at least two billion people in the next two years. Agency chief Margaret Chan has expressed concern there is not a good process in place to produce enough vaccine against the virus.
In the United States, there are now guidelines for the use of H1N1 vaccine when it becomes available. An advisory committee of the Centers for Disease Control and Prevention said there are five groups that should be vaccinated first.
These include pregnant women and people who live with or care for children younger than six months. They also include workers in health care and emergency services, and people between six months and 24 years of age.
The fifth group on the list is people 25 to 64 with chronic health problems.
If vaccine supplies are limited, then the committee says two groups of children should be vaccinated before other children. One group is those who are six months to four years old. The other is those five to eighteen with chronic medical conditions.
In April, after the first cases in the United States, officials told schools to close at the first sign of an H1N1 outbreak. The government later eased those warnings. Since then officials have been reported working on final guidelines for when schools should close.
And that's the VOA Special English Health Report, written by Caty Weaver. I'm Steve Ember.