Universal vaccines would allow wide-scale flu prevention

however, act on virus targets that are relatively constant across all types of flu, even pandemic flu. The researchers found that the vaccines could be deployed on a large scale to avert a pandemic altogether, even if only a proportion of the population received vaccination. The vaccine would raise “herd immunity,” wherein even unvaccinated individuals are protected because many people around them are immune.

Next, the researchers explored how cross-protective vaccines could combat those strains that cause flu epidemics every winter. To test how the vaccine would affect the flu virus, the researchers ran their model according to the two prevailing theories of flu evolution, including a theory a team led by Koelle reported in the journal Science in 2006.

In both cases, mass immunization with universal vaccines, maintained over several years, would slow viral evolution, or immune escape. Significantly, the researchers found that universal vaccines need not be fully protective to control flu, Arinaminpathy said. To account for any potential differences universal vaccines might have in the level of flu immunity they provide, Arinaminpathy and his colleagues assumed their hypothetical vaccine would not prevent infection, but only reduce the severity of symptoms such as coughing and sneezing, which would bring down the chances of transmitting the virus.

The researchers’ simulation showed that overall this led to fewer people becoming infected and, thus, fewer people gaining immunity to the dominant flu strain. That would remove the advantage that any new strains might have, Arinaminpathy said. At the same time, lower rates of infection would mean that fewer people could harbor mutant viruses in the first place because they never caught the original strain.

“We found that by putting the brakes on flu transmission, you could also put the brakes on flu evolution,” Arinaminpathy said. “Our model illustrates how we can control the flu this way, instead of simply reacting to it every few years.

“You can close schools and administer our current crop of vaccines and antiviral drugs as much as you want, but never realistically enough to stop transmission over any extended period of time,” he said. “With the cross-protective vaccines, we may be able to finally throw a blanket on the transmission of all flu strains over the long term in a way that can impact the virus’ evolution.”

That said, the researchers indicate that cross-protective vaccines could buttress existing vaccines that provide strain-specific immunity by keeping viral evolution in those strains to a minimum. If so, the result would be that the universal vaccine would expand the existing arsenal of flu control rather than replace it, said Lloyd-Smith of UCLA.

“Flu control has been dogged by this problem that the virus just keeps evolving. It stays one step ahead of the traditional means of controlling it. So, with strain-specific vaccines, you’re always chasing last year’s virus,” Lloyd-Smith said.

“By using the two vaccines in conjunction, we could get more mileage out of the strain-specific vaccines before they have to be changed,” he said. “That gives us an edge in the ongoing evolutionary arms race that we’re engaged in with influenza. Universal vaccines won’t get rid of the flu completely, but they should take our control efforts to the next level.”

— Read more in Nimalan Arinaminpathy et al., “Impact of cross-protective vaccines on epidemiological and evolutionary dynamics of influenza,” Proceedings of the American Academy of Sciences 109 no. 8 (21 February 2012): 3173-77 (doi: 10.1073/pnas.1113342109)