2009-10 Influenza (Flu) Season
Yes, antibodies made in response to vaccination with one flu virus can
provide protection against related viruses. This can result in reduced vaccine
effectiveness against the related viruses, but it can still provide enough
protection to prevent or lessen illness severity and prevent flu-related
complications. (However, a flu vaccine is not expected to offer
cross-protection against viruses that are very different genetically from those
in the vaccine.) In addition, it's important to remember that the seasonal flu
vaccine contains three viruses so that even when there is a less than ideal
match or lower effectiveness against one virus, the vaccine may protect against
the other two viruses. For these reasons, even during seasons when there is a
less than ideal match, CDC continues to recommend seasonal flu vaccination.
This is particularly important for people at high risk for serious flu
complications and for their close contacts.
Will the seasonal vaccine protect against the new H1N1 virus?
The seasonal vaccine is not expected to protect against the 2009 H1N1
virus because it is very different genetically from the seasonal H1N1 virus
that is in this season's vaccine. That is why the government and manufacturers
are producing a separate 2009
H1N1 vaccine designed to protect against the 2009 H1N1 virus.
What is CDC doing to monitor seasonal flu vaccine effectiveness for the
CDC carries out and collaborates with outside partners to assess the
effectiveness of seasonal flu vaccines. During the 2009-10 season, CDC is
planning multiple studies on the effectiveness of the seasonal influenza
vaccine and the 2009 H1N1 vaccine. These studies will measure vaccine
effectiveness in preventing laboratory-confirmed seasonal and 2009 H1N1
influenza infections in children, pregnant women, health care workers, and
What is CDC doing to monitor antiviral resistance in the United States
during the 2009-10 season?
Antiviral resistance means that a virus has changed in such a way that
antiviral drugs are less effective in treating or preventing illnesses caused
by the virus. Samples of viruses collected from around the United States and
worldwide are studied to determine if they are resistant to any of the four
FDA-approved influenza antiviral drugs.