News Articles
Early Vaccination Best Way
to Combat H1N1: Study
Mathematical model finds delay makes vaccinations less effective, says U of G stats prof
BY LORI BONA HUNT
Early action, especially rapid rollout of vaccines, is the best way to reduce the infection rate of the H1N1 influenza virus, according to a new study that involved Prof. Chris Bauch, Mathematics and Statistics.
But delaying vaccination by 30 days or more from the start of an outbreak significantly erodes its effectiveness, according to the paper published this month in the Cana- dian Medical Association Journal.
Bauch is one of a handful of researchers in Ontario who were approached by the Ontario Agency for Health Protection and Promotion (OAHPP) in the spring to create a mathematical model to help the province develop effective mitigation strategies against H1N1.
Their model projects how many people will be infected under different disease-control strategies. It simulated a pandemic outbreak based on demographic information from London, Ont., as well as epidemiologic influenza pandemic data.
A broad range of scenarios were introduced into the model involving vaccination timing, school closures and antiviral drug-treatment strategies as well as the effect of pre-existing immunity. The model then provided mathematical predictions under 630 different combinations of scenarios.
The researchers found that no matter the scenario, early vaccination had a disproportionately large impact on reducing the infection rate in a “fall wave” of the pandemic. For example, vaccinating 60 per cent of the population before the outbreak was found to virtually prevent an epidemic.
In addition, “vaccination in the first 30 days reduced the peak of the outbreak as much as 50 per cent,” says Bauch.
Early vaccination also helped the health-care system cope by flattening the peak, and vaccination before the outbreak further delayed the peak.
The longer vaccination is delayed, the poorer the outcome, the study found. For example, in the setting of a school or day-care closure, vaccinating 60 days after the outbreak began had little impact on the infection rate.
The researchers also discovered that, across all scenarios, having a pre-existing immunity of 15 per cent or more in the population keeps infection rates low, even if vaccination is delayed or an entire population isn’t vaccinated.
In addition, they found that a pandemic can be halted almost entirely if schools are closed early on in combination with at least some vaccination. But Bauch notes there are important social costs of school closures the study did not examine.
He says having a pre-existing model can play an important role in deciding which mitigation strategies to adopt and which ones not to, especially in future pandemics.
“You won’t have to start from scratch. The hope is that, next time around, the model can be taken off the shelf, and you just plug in new data. It will really reduce the time required to get useful projections out of the model.”
Other researchers involved in the study are from the University of Toronto, OAHPP and the Research Institute of the Hospital for Sick Children.