Dip In Air Travel Post-9/11 Delayed Flu Spread

The sharp drop in air travel after the September 11 terrorist attacks in 2001 may have slowed the spread of flu in the US, researchers have discovered.

These real-world data about ordinary flu contrast with recent computer simulations modelling the spread of pandemic bird flu. These models cast doubt on the idea that air travel restrictions could slow bird flu's spread.

The new work shows that the reduction in air travel following 9/11 may have slowed the spread of ordinary flu in the US by about two weeks in the winter. Researchers suggest that reducing the number of air passengers could give some communities a few extra weeks to prepare for a pandemic bird flu virus, should it emerge.

“Travel restrictions to infected areas may provide public health coordinators lead time to stockpile vaccine, for example,” says John Brownstein of the Children’s Hospital in Boston, Massachusetts, US, who led the new study.

The 2001-2002 flu season coincided with a 27% reduction in air travel in the month of the September 11 terror attack. That is a reduction of 1.7 million international passengers travelling to and from the US. Brownstein and colleagues have linked these figures to a two-week delay in the spread of ordinary flu within the US.

Previous computer models suggested it would take a 99% reduction in such travel to achieve this length of delay with pandemic bird flu (see Only drugs and vaccines will deflect bird flu pandemic).

“Our study suggests that you could get more benefit than the simulations show,” Brownstein says. He speculates that a 50% reduction in air travel could translate into a delay of about one month.

Live Bird Flu Vaccine Raises Hopes Of Pre-Pandemic Shots

14:11 12 September 2006
NewScientist.com news service
Debora MacKenzie

As vaccine manufacturers struggle to make a standard flu vaccine for the deadly H5N1 bird flu, US scientists have found that a totally different approach might work better.

A live synthetic virus carrying the surface proteins of H5N1, and simply squirted up the noses of test animals, has induced the kind of wide-ranging immunity necessary to make it worthwhile stockpiling vaccine before a pandemic. Tests are already underway in humans.

Most flu vaccines are injected, and contain killed virus. But H5N1 vaccine has been stubbornly ineffective prepared this way – two shots containing large amounts of virus or novel, still-unlicensed additives have been needed for recipients to develop immunity, and even then not in all people tested. H5N1 vaccine virus also grows very slowly in production plants, for reasons as yet unknown.

Worse still, what little information is available suggests that these killed vaccines do not induce immunity that cross-reacts with other strains of H5N1. This is crucial if we are to stockpile vaccine ahead of any H5N1 pandemic, as it is impossible to predict the precise strain (see Today's bird flu vaccines will have to do here).

Swift protection

So the new trials, led by Kanta Subbarao at the National Institutes of Allergy and Infectious Diseases in Bethesda, US, represent good news. The researchers used a live, weakened flu virus carrying surface proteins from H5N1. Squirted up the noses of test animals, the spray protected mice and ferrets completely after just two doses, and kept mice from dying from later H5N1 infection after only one dose.

Most importantly, vaccines made from H5N1 strains isolated in either 1997, 2003 or 2004 protected against the other viruses, and against H5N1 taken from Indonesia in 2005. These viruses have the kinds of small differences that might emerge between the H5N1 circulating now and a pandemic strain.

“We need a vaccine capable of inducing an effective human immune response against a range of H5N1 viruses that may emerge in future,” says Subbarao. While killed virus vaccines induce mainly antibodies, the live synthetic virus induces more cell-mediated immunity, based on blood cells called lymphocytes. That tends to be more broadly reactive with different strains, say vaccine experts.

The live vaccine was based on a weakened flu virus developed by Medimmune of Gaithersburg, Maryland, US, which already markets it as a nose-spray vaccine for ordinary flu. When fitted with surface proteins from H5N1 the live vaccine virus remained harmless, even to chickens, which are extremely sensitive to H5N1. Nonetheless, the 20 people who received the live vaccine in June are in isolation to prevent any virus escaping.

Journal reference: PLoS Medicine (vol 3, e360)

Although a single dose of vaccine did not induce complete protection from viral replication in the animal model, in the clinical setting this partial protection may translate to protection from severe illness and death in humans.
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Although live, attenuated influenza viruses do not transmit well, reassortment within a person vaccinated and then coinfected with wild-type influenza virus could result in a hybrid virus fully competent for replication and transmission in humans that contains the antigenically novel H5 HA, inadvertently triggering a pandemic.

This concern will limit clinical testing of the vaccine in humans and may restrict use of this vaccine approach to the period after a new pandemic strain has begun to circulate. Nonetheless, the work from Suguitan et al. is an important step along the path to influenza preparedness and warrants further development.

http://medicine.plosjournals.org/perlserv/?request=get-document&doi=10.1371%2Fjournal.pmed.0030375

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