Influenza remains for doctors. Health authorities face huge challenge. This is not only shown by the current wave of influenza in Baden-Wurttemberg.
Paris – An estimated 50 million deaths were caused worldwide by the Spanish flu between 1918 and 1920. Such a devastating flu epidemic has not been repeated so far. But as the current flu epidemic shows, influenza remains a huge challenge for doctors and public health officials. Because there are different genera and strains of flu viruses and their genomes are always changing, new vaccines must be developed every year.
Deciding which flu viruses to vaccinate against is like playing roulette. "Viruses are constantly evolving," explains Wenqing Zhang, who heads the global flu control program at the World Health Organization (WHO). "The viruses circulating this year are not necessarily the ones circulating next year."Every year, WHO experts have to decide which influenza viruses should be vaccinated against in the coming season. They rely on data from a network of national flu centers in 114 countries that monitor the spread of flu viruses and collect samples from patients.
Twice a year WHO recommendations
The WHO ies its recommendations twice a year: in February for the northern hemisphere and in September for the southern hemisphere. Based on WHO recommendations, pharmaceutical companies develop the new vaccine – mostly by growing flu viruses in chicken eggs and putting the viruses in attenuated form in the vaccine doses. This involves combining three or four viruses – two of genus A and at least one of genus B. Because of this lengthy process, it takes eight to ten months for a new vaccine to be ready.
"We can't say for sure which viruses will be circulating in eight months," Zhang admits. "So we're relying on the best possible surveillance and analysis system to make that bet, that prediction."Flu viruses have an enormous capacity to mutate," explains microbiologist Vincent Enouf of the renowned Institut Pasteur in Paris. On the one hand, there are minute genetic changes in the reproduction of the viruses. On the other hand, it happens that different subgroups of influenza genus A exchange genetic material with each other, resulting in a completely new strain of viruses.
Such new virus strains trigger a pandemic every few years or decades. The deadliest influenza epidemics after the Spanish flu were the Asian flu in 1957, the Hong Kong flu in 1968 and the swine flu in 2009. Even in the absence of such a pandemic, the WHO estimates that between 290.000 and 650.000 people from influenza, in three to five million cases there is a severe course of the disease. And even if it's just a cold, cough, sore throat and fever, the economic impact in terms of medical care costs and sick leave is enormous.
Physicians dream of a universal vaccine
Physicians dream of a universal vaccine that protects equally against all influenza viruses. Several such vaccines are currently being tested – but with uncertain outcomes. Influenza is one of the best-researched viruses, says virologist David Evans of Saint Andrews University in Scotland. However, it is also a fact that "it is very difficult to control". So it's only a matter of time before humanity faces another flu pandemic, says Wendy Barclay, a flu expert at Imperial College in London.
Unlike during the Spanish flu, antibiotics are available today that can combat dangerous concomitant diseases caused by bacteria, such as pneumonia or bronchitis. Still, the consequences of a new pandemic could be "very bad," Barclay warns. Mankind will have to live with that, says Evans. She will continue to be constantly exposed to the threat of influenza – and "probably forever".