Influenza is a serious public health threat. No infectious disease has higher rates of incidence and mortality. Worldwide, a third of all children and 10% of all adults are infected with influenza viruses every year. Influenza and its serious complications cause a half a million deaths annually.
Vaccination is the primary means of preventing influenza infections and their spread, but conventional influenza vaccines are only about 50% effective at best. Effectiveness of conventional vaccines relies on a good match between the strains on which the vaccines are based and strains circulating in populations. As influenza viruses replicate they undergo constant genetic change. The gradual accumulation of genetic changes results in “drifted” strains that can’t be recognized by antibodies generated by prior immunization or virus exposure. Conventional vaccine technologies require annual attempts to match influenza vaccines to the strains expected to dominate the coming flu season. Mismatches between vaccines and circulating strains frequently occur, resulting in poor protection.
Occasionally influenza viruses undergo an abrupt genetic change so significant that most people have no immunity to the new virus strain. Such “shifted” strains can cause an influenza pandemic. Rapid development, production and distribution of a new vaccine is paramount to protect the population and forestall the disease’s spread. Pandemic influenza is a relentless global threat. The 2009 influenza pandemic led to over a quarter of a million deaths. The three major influenza pandemics of the 20th century caused a combined total of over 50 million deaths.