BACKGROUND: Emerging data suggest that pregnancy conveys high risk for severe 
complications from the 2009 pandemic influenza A virus (2009 H1N1) infection.
CASE: We describe an infected pregnant woman with critical illness owing to 
acute respiratory distress syndrome despite previous vaccination. Early 
serologic testing indicated absent immunity, followed 11 days later by a robust 
immune response. The patient required mechanical ventilation for 11 days, but 
ultimately improved, and was discharged home on hospital day 14.
CONCLUSION: With the expectation that 2009 H1N1 will continue to cause disease 
in the immediate future, the virus has been included as a component of the 
2010-2011 seasonal influenza vaccine. Vaccination of pregnant women is strongly 
encouraged. However, regardless of vaccination history, clinicians should remain 
vigilant for 2009 H1N1 infection when the virus is in circulation, and should 
not delay antiviral treatment of pregnant women with suspected influenza.