Epidemiological impact of the paediatric live attenuated influenza vaccine (LAIV) programme on group A Streptococcus (GAS) infections in England

Influenza is known to predispose to secondary bacterial infections including group A streptococcal infection (GAS) and invasive (iGAS) disease. The universal paediatric live attenuated influenza vaccine (LAIV) programme was introduced in England during the 2013/14 influenza season to directly protect children as well as indirectly protect the wider population through reduction in transmission. Nationally, the programme was implemented incrementally introducing cohorts of children from pre-school age to school age children year on year towards 2 to 16 year old coverage. In addition, a series of discrete geographical areas (pilot areas) offered LAIV vaccination to all primary school age children, allowing for a unique assessment and comparison of infection rates between pilot and non-pilot areas during roll-out. Overall reductions in incidence rates of GAS and scarlet fever were observed within most of post-LAIV programme seasons when assessing the impact of the LAIV programme among the targeted (2 to 4 years and 5 to 10 years) and non-targeted groups using incidence rate ratios (IRRs) from Poisson regressions. We assessed the overall effect of the pilot programme between the pre-introduction (2010/11-2012/13 influenza seasons) and post-introduction (2013/14- 2016/17 influenza) periods using negative binomial regression by comparing the pre- to -post programme changes in incidence between the pilot and non-pilot areas (rIRR = ratio of incidence rate ratios). This showed significant reductions among the 5 to 10 years (rIRR of 0.57 (95% CI: 0.45 to 0.71; p-value: <0.001)); the 2 to 4 years (rIRR of 0.62 (95% CI:0.43 to 0.90; p-value: 0.011)) and the 11 to 16 years (rIRR of 0.63 (95% CI: 0.43 to 0.90; p-value: 0.018)) for GAS infections. A non-significant reduction was also seen for iGAS in 2-4 year olds (rIRR of 0.58 (95% CI: 0.21 to 1.65; p-value=0.31)). No difference was seen for iGAS 5 to 10 year olds, or for scarlet fever in both age groups (rIRRs (95% CI) of 1.1 (0.34-3.6), 0.96 (0.66-1.39), 1.16 (0.75-1.81) for iGAS age 5 to 10, scarlet fever age 2 to 4 and 5 to 10, respectively). Our findings are compatible with the paediatric LAIV programme reducing the incidence of GAS and iGAS infections among children and support attaining high uptake of childhood influenza vaccination.