The Lancet Infectious Disease
Oct 2011  Volume 11  Number 10  p721 – 800
http://www.thelancet.com/journals/laninf/issue/current

Herd immunity and serotype replacement 4 years after seven-valent pneumococcal conjugate vaccination in England and Wales: an observational cohort study
Elizabeth Miller, Nicholas J Andrews, Pauline A Waight, Mary PE Slack, Robert C George

Preview
Despite much serotype replacement, a substantial reduction in invasive pneumococcal disease in young children can be achieved with PCV7 vaccination, with some indirect benefit in older age groups. Further reductions should be achievable by use of higher valency vaccines. Robust surveillance data are needed to properly assess the epidemiological effect of multivalent pneumococcal disease vaccines.