PRE-PANDEMIC VACCINATION MAY HALT THE SPREAD OF A PANDEMIC

MATHEMATIC MODELING

CROSS PROTECTION

Avian H5N1 influenza vaccination – now?

PRE-PANDEMIC PANDEMIC

3-4 weeks

?

Months or years

Direct protection Manufacturing of pre-pandemic vaccine

Currently, at-risk population (poultry

workers, vets, lab workers etc for vaccination now?)

WHO Pandemic

Alert

Longini et al. Science 2005; 309: 1083-1087

Prepandemic vaccines may halt the spread and significantly reduce the impact of a pandemic (mathematical modelling)

Rural population of 500,000 in ThailandAssumptions:

• start intervention after 21 days

• TAP (targeted antiviral prophylaxis)

• low vaccine efficacy

– A vaccine efficacy for susceptibility (VES) of approximately 30% (30% reduction in probability of being infected upon exposure)

– A vaccine efficacy for infectiousness (VEI) of approximately 50% (50% reduction in probability of infecting someone else through contact)

Practical example of modeling

Mathematical models have demonstrated that prepandemic vaccines may halt the spread and significantly reduce the impact

Longini et al. Science 2005; 309: 1083-1087

*Targeted antiviral prophylaxis

Simulated pandemic influenza outbreak (R0 = 1.7) without intervention compared to 80% TAP + 50% vacc.

With Intervention (pre-pan vacc plus TAP)

Without intervention

Vaccination as early as Day 30 could help reduce impact of pandemic

Cumulative attack rate

Vaccination from day 90

Vaccination from day 60

Vaccination from day 30

No Vaccination 34%

1%

13%

31%

0% 10% 20% 30% 40%

Most people are likely to be exposed to pandemic flu before they can be vaccinated

Policy of mass vaccination assuming 1% of the population can be vaccinated per day

Ferguson et al. Nature 2006; 442(7101):448-52

US Model