Emergencies preparedness, response

Use of the pandemic (H1N1) 2009 vaccines

30 October 2009

How is the vaccine given?

Some vaccines contain inactivated (or killed) viruses. These vaccines are given by injection into the upper arm for most people. In infants and younger children the thigh is the preferred site for the vaccine shot.

Another type of vaccine is made with live viruses, and it is administered by nasal spray.

Both are protective against influenza.

Do people need one dose or two doses of the vaccine?

Immunization experts recommend a single dose of vaccine in adults and adolescents from 10 years of age and above, provided this use is consistent with regulatory authorities' indications. More study is advised on effective dosage regimens for immuno-suppressed persons for whom two doses of vaccine may be needed. Where national authorities have made children a priority for early vaccination, experts are advising one dose of vaccine to as many children as possible over the age of 6 months and younger than 10 years of age. Recommendations on numbers of dosages may need to be adapted rapidly as new data emerges.

Is there anyone who should not have the inactivated pandemic vaccine?

Yes. As general rule, inactivated vaccines should not be administered to:

  • People with a history of anaphylaxis (or hypersensitive reactions), or other life-threatening allergic reactions to any of the constituents or trace residues of the vaccine;
  • People with history of a severe reaction to previous influenza vaccination;
  • People who developed Guillain-Barré syndrome (GBS) within 6 weeks of getting an influenza vaccine;
  • Children less than 6 months of age (inactivated influenza vaccine is not approved for this age group);
  • People who have a moderate-to-severe illness with a fever (they should wait until they recover to get vaccinated).

Product package inserts provide information on who should not get specific vaccine products.

Can the pandemic influenza vaccine be administered simultaneously with other vaccines? What about with the seasonal influenza vaccine?

Inactivated influenza vaccine can be given at the same time as other injectable, non-influenza vaccines, but the vaccines should be administered at different injection sites.

Seasonal influenza and pandemic influenza vaccines can be administered together, and there is a public health value in doing so, according to a global panel of immunization experts. Clinical studies on this area of vaccine administration are continuing.

How can a person who wishes to be vaccinated against the pandemic influenza receive the vaccine?

National health authorities will decide how to implement national pandemic influenza vaccination campaigns. They will know best about whether and where pandemic influenza vaccine is available, and how people can get vaccinated.

Will pandemic influenza vaccines protect against other influenza viruses, such as the seasonal influenza?

The pandemic influenza vaccines are not expected to provide protection against other influenza viruses.

Since current seasonal influenza vaccines do not contain the pandemic virus, people should be vaccinated against both pandemic influenza and seasonal influenza. In the future, the situation could change.

Is there a risk of catching illness from the vaccine itself?

Inactivated vaccines contain killed viruses or parts of viruses, which cannot cause disease. Live influenza vaccine contains weakened influenza virus that multiplies poorly but is unable to cause disease.

Both vaccines can cause some flu-like side effects (e.g. muscle ache, fever) but the symptoms, sometimes associated with vaccination, are generally less pronounced and of much shorter duration.

Why do some people who have been vaccinated still get influenza?

There are some reasons why some people believe they have gotten influenza after vaccination. No vaccines, including pandemic influenza vaccines, provide 100% protection against disease. But they do greatly reduce the risk of disease. Also, influenza vaccines only become effective about 14 days after vaccination. Those infected shortly before (1 to 3 days) or shortly after immunization can still get the disease.

Vaccinated individuals can also get influenza caused by a different strain of influenza virus, for which the vaccine does not provide protection.

Finally, people who have received influenza vaccine can later have an illness, caused by other common viruses that are not influenza, but be mistaken for the flu. In all of these instances, a person could believe that the vaccine failed to protect them or that vaccine caused the disease when neither conclusion is accurate.

(updated from 12 July 2009, 27 May 2009 and 2 May 2009 versions)