October 20, 2010

A Third H1N1 Pandemic Wave In 2010 Is Unlikely

(Ivanhoe Newswire) -- H1N1 "“ frequently referred to as swine flu by the public "“ is a subtype of influenza A virus.  This novel infectious disease was the most common cause of human influenza (flu) in 2009, and has caused nearly 17,000 deaths by the start of 2010.  A recent study however suggests that a third pandemic wave is unlikely, stating worldwide flu activity is expected to return to typical seasonal patterns.

Researchers from the BC Centre for Disease Control, University of British Columbia and BC Biomedical Laboratories embarked on a study that compared blood levels of antibodies against the H1N1 influenza before and after the 2009 pandemic.  The flu findings came from 1,127 people in British Columbia's Lower Mainland of all ages, spanning from 9 months to 101 years.

Samples collected prior to the pandemic showed that less than 10 percent of children as well as adults fewer than 70 years of age had protective levels of H1N1antibodies.  Conversely, 77 percent of people over  80 years of age had protected levels.  After the waves of infection and the fall 2009 immunization campaign, researchers discovered a 70 percent protection rate in people under the age of 20, yet lower seroprotection rates in adults aged 20 "“ 49 (44 percent) and 50 "“ 79 years of age (30 percent).  It was reported that people between the ages of 70 "“ 79 had the lowest rate of antibodies (21 percent) whereas those over 80 years of age had significantly higher rates.

"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," which Dr. Danuta Skowronski, BC Centre for Disease Control and University of British Columbia, with coauthors was quoted as saying.

Researchers estimated that a community-level protection above 40 percent would be sufficient in averting a large epidemic in a population, particularly if school children that usually contribute to most of the spread of influenza are protected.  Given that the overall seroprotection rate is estimated at 46% and 70% in school-age children, "these findings reassure against the likelihood of a substantial third pandemic H1N1 wave during the 2010-11 season, unless there is a significant waning of antibody or change in the virus" the authors add.

SOURCE: Canadian Medical Journal, October 2010