Weakened flu virus to make more effective vaccine

A "rewritten" flu virus sets off an identical immune response in mice to a natural infection, suggesting it could make a more effective vaccine than traditional options.

The new vaccine virus contains identical proteins as the flu strain it targets, with only one major difference: its genome has been rewritten to produce a virus that replicates too slowly to cause any trouble.

"It's unlike anything nature ever evolved," The New Scientist quoted Steffen Mueller, a virologist at Stony Brook University in New York, whose team tested the vaccine in mice, as saying.

The team took advantage of a quirk in the genetic code to weaken the virus without changing the proteins it contains. Three-letter DNA sequences called codons control which amino acids get assembled into a protein. However, with more three-letter combinations than there are amino acids, more than one codon can produce the same amino acid.

Organisms have their favourites - preferring some codons over others because they translate into proteins more efficiently, according to Mueller.

His team exploited this quirk to engineer a flu virus that contains thousands of genetic alterations that result in unfavourable combinations of codons.

Mueller said: "We call this death by one thousand cuts."

Each alteration is almost insignificant by itself, but together they create a weakened virus that does not replicate well.

Mice that were given the vaccine stayed healthy.

After four weeks, they were infected with a dose of flu that would ordinarily kill them.

Three days later, 80% of the mice had no detectable flu virus in their system.

Mueller believes the rewritten virus should elicit a stronger immune response than traditional vaccines because it would expose the immune system to proteins identical to the ones seen in seasonal or pandemic flu strains.

The study appears in Nature Biotechnology.