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- Pertussis vaccinations: waning immunity and low effectiveness Norway 2012 study
- Incidence in children under the age of five years has not changed much over the fifteen year time period, however incidence in teenagers and young adults (10–40 yrs) has increased dramatically. Children between the ages of five and ten years experienced an increase in incidence from 1997 until the introduction of the childhood booster vaccine in 2006, and have now returned approximately to their 1997 levels. In contrast, there was a milder downturn in incidence in 10–19 year olds in 2006, followed by an increase a few years later."<br /><br />"By age 14 over 90% of cases occurred in vaccinated hosts, which, in the absence of loss of immunity, would indicate vaccine efficacy below 30%. These results therefore provide strong evidence that vaccine-induced immunity wanes over time.