Simple catalytic model to determine the optimal age to vaccinate

Figure1: Model output from fitting the catalytic model

Respiratory syncytial virus has been recognized as a major viral cause of childhood pneumonia and is currently an important vaccine candidate. Prior to the introduction of a vaccine in a population, it is crucial to understand the background transmission dynamics in order to optimize vaccine delivery. Mathematical models have often been used to explore vaccination strategies and advise on optimal delivery. The more complicated dynamic models can provide detailed answers on who, when and how to vaccinate.

We used a simple catalytic model to determine the optimal age to vaccinate as suggested by age-seroprevalence data. This catalytic model estimates an average rate of infection based on the pattern of seroprevalence with age, in addition we estimated the rate of decay of maternal antibodies and calculated an average age of primary infection. We obtained estimates of 0.78/person/year for the rate of infection in the under 1 year age group and 1.69/person/year in the older age groups, leading to an average age at primary infection of 15 months.

The optimal vaccination window, defined here as a time point where on average maternal antibodies have been lost but the infection rate is not too high, is between 5 and 12 months. This is in line with previous findings from a dynamic age-structured model, and adds on to the growing body of evidence on the targets for an RSV vaccine.