– US invokes emergency act to keep H7N9 flu at bay (New Scientist, May 8, 2013):
THE US government has declared that H7N9 bird flu “poses a significant potential for a public health emergency”, and has given “emergency use authorisation” for diagnostic kits for the virus. This means tests can be used that haven’t gone through the usual lengthy approval process by the US Food and Drug Administration.
They are right to be concerned. H7N9 could be a tough adversary: New Scientist has learned that it provokes a weaker immune response than most flu, making vaccines hard to produce.
Although H7N9 is not, so far, transmissible between humans, it does cause severe disease in people, is easier to catch than other bird flu strains, and may need only a few mutations to go pandemic. The UK has already given doctors instructions on when to test people for H7N9, and how to manage any with the virus.
The US’s emergency authorisation will allow the use of a kit that looks for flu genes using a polymerase chain reaction test, which has been made specific for H7N9. The kit has had preliminary tests but would normally need more exhaustive tests to be approved. Innovative new diagnostics should eventually be authorised too, says Charles Chiu of the University of California in San Francisco.
This kind of fast, high-throughput screening for pandemic flu, possibly at borders, might allow early cases to be treated with antiviral drugs, potentially slowing the spread of the virus while vaccines are made.
The next emergency authorisation is likely to be for immune-stimulating chemicals called adjuvants to put in those vaccines. These were used in vaccines in Europe and Canada during the 2009 pandemic, but adjuvants suitable for flu are not currently approved in the US.
Labs are now making “seed” viruses for manufacturers to create H7N9 vaccine. That process faces the same development delays as in 2009, when vaccine arrived too late for most people.
But there is another problem: H7 flu is poor at stimulating immunity. Virologists at the European Flu Summit in Brussels last week told New Scientist that early results show 13 times more H7N9 virus is needed to elicit a protective immune response than is needed for ordinary flu. That’s bad news: the more virus a vaccine requires, the fewer doses that can be grown in a given time.
“H7N9 may be a ‘stealth’ virus that is able to fly under the immune system’s radar,” says Anne De Groot of the University of Rhode Island at Providence. That’s because its surface protein haemagglutinin doesn’t contain many short amino acid sequences – called epitopes – that trigger helper T-cells in the body to stimulate antibody-making cells.
“H7N9 is not very immunogenic, because the epitopes have a very weak signal,” says Masato Tashiro, head of flu at Japan’s National Institute of Infectious Diseases in Tokyo. People differ genetically in the epitopes their T-cells recognise, and his lab has found that Asian people could be especially vulnerable.
Adjuvants might make vaccines containing less virus more effective, meaning doses can be produced faster. However, children in northern Europe who received adjuvanted flu vaccines in 2009 had slightly higher rates of narcolepsy than normal. Epidemiological studies so far do not show whether the adjuvant was the cause, says Miriam Sturkenboom of Erasmus Medical Center in Rotterdam, the Netherlands. The US is now funding a large study of countries that used adjuvanted vaccines in 2009 to see if they may have caused narcolepsy.
This article appeared in print under the headline “US evokes emergency act to keep flu at bay”