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Every year, flu vaccine manufacturers develop and produce new versions at enormous expense to take on the latest circulating influenza strain due to the constantly evolving nature of viruses. The US military's Defense Advanced Research Projects Agency (Darpa) has now launched a programme that aims to create vaccines that can adapt to fight these fast-changing viruses.

As our bodies come up with new immune responses, viruses have the ability to mutate and morph as they reproduce within their hosts, rendering a vaccine that could work today, useless tomorrow. The US military's R&D organisation has launched an Interfering and Co-Evolving Prevention and Therapy (Intercept) programme that hopes to develop a solution that can outpace evolving pathogens, adapt in real time and shape-shift as quickly as viruses do.

"We need a new paradigm to stay ahead of these moving targets," Darpa programme manager Jim Gimlett said in a statement. "With Intercept, the goal is to develop viral therapies that are effective against a broad spectrum of viral strains, and that can co-evolve and outpace new strains."

All viruses consist of two main parts — genetic material surrounded by a protein shell. When a virus attaches itself to a cell within a host, it releases its genetic material into that cell to reproduce, hijacks its biological machinery and forces the cell to create new copies of the viral genome and shell proteins. Inside the cell, the new viral genomes and protein shells gather to create new viruses that eventually burst out of the cell and infect other cells as well.

Intercept is looking to tap into tiny engineered, virus-like particles called therapeutic interfering cells, or TIPs, to compete with viruses. Similar to viruses, TIPs can also enter host cells but don't affect them. However, when a cell that contains a TIP does get infected by a virus, the cell produces TIP genome copies that can compete with the virus's genome copies for protein shells and reproduce faster than the virus to create more TIP-containing cells. As more "dud viruses" containing harmless TIP genes are created to dilute the real viruses, the impact of any viral load is significantly reduced.

Since they are made of genetic material, Gimlett says TIPs can also mutate and diversify just as genomes of real viruses do as well.

"You can think of these TIP-filled envelopes as tiny Trojan horses, but instead of containing warriors they contain pretenders that ultimately outnumber real disease-causing viruses and interfere with their ability to replicate," Gimlett said. "Once we develop a TIP that works for a given virus, we expect it to generate a steady stream of variants so there will always be a population of TIPs with the right genetic stuff to disrupt any new strains of that virus that may arise."

Since the programme has just launched, Darpa still has a long way to go to develop TIP candidates, conduct long-term tests and adjust them accordingly through computer models. However, if successful, they could prove extremely useful to tackle several viral strains that emerge and evolve every year, no matter how severe they are.

According to the World Bank, a single severe flu pandemic could cost the global economy a whopping $3 trillion (£2.1 trillion).

When the Ebola epidemic seemed to be contained in March 2015, Bill Gates warned that "there is a significant chance that an epidemic of a substantially more infectious disease will occur sometime in the next 20 years." In the same month, Brazil notified WHO of reports of a mysterious rash-causing illness spreading across northeastern states, which was later identified as the Zika virus. Since then, it has spread explosively to become the world's largest Zika outbreak ever, reaching more than 30 countries and territories.