New study sheds light on influenza outbreak dynamics
An international team of scientists has developed a new model to help predict influenza outbreaks and the efficacy of vaccines in treating them. The partly EU-funded study, published in the journal Science, links the evolution of the virus to the immunisation rates needed to prevent an outbreak in the population. The findings could ultimately increase our understanding of the dynamics of a wide range of infectious diseases. Part of the financial support for this research, that brought together researchers from the Netherlands, the UK and the US, came out of the EMPERIE ('European management platform for emerging and re-emerging infectious disease entities') project, funded under the Health Theme of the Seventh Framework Programme (FP7). Influenza viruses increase their chance of tricking their host's immune system by substituting different amino acids at key molecular points. The greater the number of differences between the strain that someone was originally vaccinated against and the new strain, the greater the likelihood of the individual becoming and remaining infectious for a longer time. The researchers worked with equine influenza: 'Equine influenza vaccines have been used, particularly in racehorses, since the 1960s,' the study says. 'For more than 40 years, all equine influenza infections have been caused by strains of the H3N8 subtype, which has a similar course of infection to seasonal influenza A in humans.' The new study found that once two or more amino acids had been substituted, outbreaks began to occur. Likelihood of infection and in turn extensive outbreaks once again increased if the host's immune system perceived the new virus and the one it had been immunised against as two completely different strains. As individuals in a population will have been immunised against different strains depending on when they were vaccinated or infected and some will not have any immunity at all, the scientists also determined that the degree of variability of immunity in a population is a key factor when it comes to the risk of an outbreak. In the end, the scientists hope that their findings will help public health officials assess the usefulness of a vaccine based upon its relationship to the current influenza strain and the population's immunity level. 'This research is ... pertinent to the use of vaccines to control pandemic influenza,' the paper continues. 'Prepandemic vaccines have the advantage that they can be used prophylactically, and can be rapidly dispatched to at-risk populations in the event of a crisis, but are unlikely to be a perfect match to circulating strains. Our work shows that even these vaccines can provide a benefit to the population; increasing the proportion of the population vaccinated can offset an imperfect match between strains. 'The ultimate goal is to directly link these results to epidemic dynamics, which is a realistic objective as influenza sequence data continues to accumulate,' the study concludes. 'The ideas presented here could extend to a broad class of infections, including emerging, re-emerging and extant infectious diseases.'
Countries
Netherlands, United Kingdom, United States