Higher population-wide protective antibodies rates have health officials hopeful that an influenza A (H1N1) pandemic will not occur again this influenza season, according to study results published this week in CMAJ.

However, continued vaccination efforts are vital to protect certain vulnerable age groups, particularly people aged 50 to 79 years.

Canadian researchers analyzed serum samples collected from 1,127 lower mainland British Columbia residents aged 9 months to 101 years between May 8 and 21, 2010.

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They determined that although protective antibodies increased among all age groups, seroprotection was lowest among people aged 70 to 79 years at 21% and among those aged 50 to 79 years at 30%.

The highest seroprotection rates occurred among people aged 90 years and older at 88%, and among the younger than 20 and older than 80 age groups, who had seroprotection rates at about 70% each. Rates among people aged 20 to 49 years were 44%.

“The higher percentage with seroprotection we observed in the young may have resulted from higher pandemic H1N1 infection rates and earlier prioritization of pandemic H1N1 vaccine to young children,” the researchers wrote.

Prior to the 2009 pandemic, seroprotection rates were estimated to be less than 10% among children and adults aged younger than 70 years old.

“Our findings support a shift from the prioritized immunization of the young that occurred in Fall 2009 to prioritized immunization of older adults for the coming 2010-2011 influenza season to protect against severe outcomes,” the researchers wrote.

Community wide seroprotection rates of 40% or more are believed to sufficiently protect against a large influenza epidemic.