Despite successful control of many infectious diseases since the 19th century, viral diseases remain an important and significant health burden in the 21st century. In fact, the turn of the 21st century saw the emergence of not only new but also re-emergent pathogens such as SARS, MERS, West Nile, Ebola, dengue and Zika viruses. In addition, the modern world is highly mobile and interconnected. The spread of infectious diseases is imminently only a flight away. It is thus of no surprise that epidemics in this century are happening at a much faster pace and spreading quicker to cause disruption to human health, society and the economy. Vaccination, particularly with a live attenuated vaccine (LAV), which has the most successful track record among the various forms of vaccines, remains the most economical public health tool available to prevent or stop the spread of infections and alleviate human sufferings. Rapid mass vaccination of at risk populations to establish herd immunity has been successfully employed to control sporadic YF outbreaks in Africa and South America. More recently, a clinical trial showed that ring vaccination of contacts with Ebola patients completely abrogated secondary virus spread. Vaccination in times of pandemics, however, cannot be limited to children but must include adults in order to rapidly elevate herd immunity rates to halt further transmission.

The use of LAV in adults has several important challenges that have not been systematically addressed. The population demographics in Singapore, like most developed countries have changed drastically over the past 3 decades. Along with improved nutrition, populations are now living longer but with increasing prevalence of chronic diseases such as obesity and dyslipidemia. Consequently, the anti-cholesterol group of drugs, with pleiotropic properties, statins, are among the commonest drugs prescribed globally for the prevention of secondary cardiovascular and major vascular complications. There is presently a mounting concern that the anti-inflammatory and immune-modulatory effects of statins could have a detrimental effect on vaccine efficacy. Indeed, studies examining inactivated influenza vaccination in older individuals had observed lower immunogenicity and overall efficacy with statin use. Whether statins have a similar negative immunogenicity effect on LAV remains undefined. The anti-inflammatory effects may dampen innate immune responses critical for triggering adaptive immunity resulting in reduced immunogenicity. Conversely, the suppression of innate immune responses could favor LAV infection and replication, allowing adaptive immune cells a longer period to sense the antigen, become activated and differentiated for improved immune response.

In this study, an experimental medicine investigation that leverages on a recently completed clinical trial that the PI led examining how cross-reactive antibodies altered the immunogenicity of yellow fever (YF) vaccination. We will seek to clarify the effects of statin on LAV immunogenicity. YF vaccine is an excellent LAV, which remains the WHO recommended response to the ever-present threat of YF outbreak. It has also served as an important model for studying human antiviral immunity. We propose to test the hypothesis that long term statins therapy alters YF LAV immunogenicity by coupling the power of a clinical trial with comprehensive systems vaccinology to define the impact statins have on the adaptive immune response to YF vaccination. This study will elucidate how statins modulate the networks that drive immunity to vaccination in a fast growing population globally. Knowledge on how statins impact LAV immunogenicity would inform public health authorities on the size of the general population that should be vaccinated to compensate for alterations in immunogenicity in this subpopulation to achieve sufficient herd immunity for epidemic and pandemic control.