Immunization is a key and highly successful tool in the fight against a range of infectious diseases, but is associated with a considerable cost, with the UK spending in excess of £200 million per year on vaccines and vaccine delivery. Infectious disease and health economic models are therefore necessary to assess whether any change in the immunization programme is cost-effective; that is, whether the value placed on health benefits or improvements in social welfare that ensue are less than the incremental cost associated with the change in programme.
The University of Warwick has considerable experience and expertise in this area, with the assembled team serving on the several government advisory boards associated with public health. The team brings cutting-edge research techniques in mathematical modelling and health economics to provide a complementary second opinion on the work undertaken in this area by the Health Protection Agency (soon to be Public Health England, PHE). Warwick has a strong international reputation for work on a range of infectious diseases and providing measured policy advice to a number of government agencies.
Through regular meetings with the Department of Health (DH) and PHE we ensure that our programme of dynamic and health economic modelling on infectious diseases meets the needs of DH, and reports are presented in a way that is of immediate use to policy-makers. In particular, we outline assumptions made, highlight gaps in the necessary data and define how these affect the interpretation of the results. Two other methods are being used to validate our conclusions: firstly, we seek to publish our findings in appropriate journals thereby opening our results to peer-review by the wider international academic community; secondly, we compare our predictions to changes in disease incidence and other health outcomes that follow changes in vaccine policy.
Human Papillomavirus (HPV)
The first disease that we have been investigating is HPV, a sexually transmitted infection (STI) that can lead to cervical cancer in women, and genital warts in both sexes. There are multiple strains of the virus, with types 16 and 18 being strongly correlated with cervical intraepithelial neoplasmia (CIN) in women, and types 6 and 11 shown to cause genital warts.
There are currently two HPV vaccines available commercially, a bivalent vaccine (Cervarix) protecting against the cancer-causing strains, and a quadravalent vaccine (Gardasil) which additionally protects against the main warts-causing strains. The UK NHS originally vaccinated teenage girls (aged 12-13) with the bivalent vaccine, starting in 2008, although has recently switched to the quadravalent vaccine. A nonavalent vaccine (protecting against 9 HPV strains, including the four mentioned above) is currently in development, and a cost effectiveness analysis will be undertaken by the MEMVIE team in due course.
The work Warwick has undertaken is to evaluate the current vaccination strategies employed, and to test the cost-effectiveness of a suite of alternative strategies. The first step is to accurately capture the dynamics of HPV transmission, by developing novel mathematical models simulating sexual partnerships between individuals. To aid with this we are employing the three NATSAL (National Survey of Sexual Attitudes and Lifestyles) surveys undertaken in the UK in 1990, 2000 and 2010, which asked a subpopulation of the UK a variety of questions related to their history of sexual partnerships, along with attitudes towards a variety of sexual practices (for example, homosexuality, and polygamy within relationships). We are using available empirical studies on pre-vaccination HPV levels to fit our model to, and once we are conrident of capturing the salient aspects of HPV transmission, we will test a variety of vaccination strategies, including the current NHS policy (teenage girls). For this we will use economic models that accurately estimate costs to the NHS for each case of HPV and, where appropriate, cervical cancer caused by HPV), and compare this to the cost of distributing the HPV vaccine and its efficacy (current estimated to protect individuals for 20 years).
Pertussis (whooping cough)
Pertussis is a highly infectious respiratory illness, caused by the bacterium Bordetella pertussis. Its main symptom is bouts of uncontrollable, violent coughing, giving it the nicknames "whooping cough" and "the hundred-day cough". It is particularly dangerous for infants, and can be fatal for newborn babies. A vaccination program has been in place in the UK for sometime now, the vaccine given along with those for tetanus and polio, as the DTP vaccine.
The UK government is now considering a "cocooning" strategy to provide additional protection to newborn babies, by vaccinating other household members (i.e. fathers and siblings). We have performed a cost-effectiveness analysis of this strategy, compared with the maternal vaccination program already in place. We are currently preparing a manuscript for publication with the results of this analysis.
We are currently doing scoping work on a number of diseases for which there are active vaccination programs in the UK, and that the Department of Health are particularly interested in independent modelling work. These include the pneumococcal vaccine (PCV) and influenza.
Matt Keeling (Professor, joint between Warwick Mathematics Institute and School of Life Sciences)
Stavros Petrou (Professor in Health Economics, Warwick Medical School)
Graham Medley (Professor, London School of Hygiene and Tropical Medicine)
Sophie Staniszewska (leader of Patient and Public Involvement, Warwick Medical School)
Martin Underwood (Director of Clinical Trials Unit, Warwick Medical School)
Samik Datta (postdoctoral researcher, Warwick Mathematics Institute and School of Life Sciences)
Tinevimbo Shiri (postdoctoral researcher, Clinical Trials Unit, Warwick Medical School)