WHO report calls H5N1 vaccine stockpiling premature

November 3, 2006

WHO report calls H5N1 vaccine stockpiling premature Roos News Editor

http://www.cidrap.umn.edu/cidrap/content/influenza/avianflu/news/nov0206who.html

Nov 2, 2006 (CIDRAP News) – A group of influenza experts convened by the World

Health Organization cautioned today that governments shouldn't stockpile

" pre-pandemic " H5N1 influenza vaccines now, because too little is known about

the requirements for an effective vaccine.

The group of 22 scientists, who met for 2 days in September, " agreed that

governments should not rush to place orders for pre-pandemic vaccines when so

many fundamental scientific questions are still outstanding, " says their report.

The United States and some other countries have been stockpiling H5N1

vaccines, despite lack of assurance that they would be effective against a

pandemic strain. Switzerland recently announced plans to buy enough vaccine for

the entire Swiss population.

The 16-page report, titled " Influenza Research at the Human and Animal

Interface, " emphasizes the continuing seriousness of the threat posed by the

H5N1 virus. The meetings on which it was based involved many of the world's

leading experts on influenza.

The experts agreed that " the seriousness of the present situation, including

the risk that a pandemic virus might emerge, is not likely to diminish in the

near future, " the document states.

The report also warns that if the H5N1 virus becomes a pandemic strain, it

could remain as lethal for humans as it is now, depending on how it acquires the

ability to spread from person to person. The current case-fatality rate, with

256 cases and 152 deaths, is about 59%.

If the virus becomes more transmissible by acquiring genes from a

human-adapted flu virus, its deadliness " would most likely be reduced. " But if

it remains " a wholly avian virus " that adapts to humans through a series of

mutations, it could remain as deadly as it is now, the experts say.

The report says that vaccine development results so far " have not been

promising, " in part because H5N1 viruses have branched off into a number of

diverse subgroups, and vaccines that seem to work against one clade, or group,

don't work well against others.

Many fundamental questions about vaccine development remain to be answered,

the group concluded. For example, scientists need to determine which adjuvant

(general immune system stimulant) works best and to define what kind of observed

immune response indicates an adequate level of protection against the actual

virus.

The experts say the idea of intradermal injection (injecting vaccine just

under the skin instead of into muscle) as a way to stretch vaccine supplies

" does not look promising and is not likely to be suitable for worldwide use. "

The document cites an urgent need for international standards for evaluating

the efficacy of pandemic vaccines. " On such an important matter, it is unwise to

leave assessments of appropriate vaccines to competing manufacturers, " it

states.

The report describes human H5N1 disease as " fundamentally different " from

ordinary flu, marked as it typically is by progressive viral pneumonia, acute

respiratory distress, and sometimes diarrhea and liver dysfunction. The

disease's severity may be a result of the " cytokine storm, " or flood of chemical

messengers causing intense inflammation in the lungs, but it is not clear

whether the cytokine storm is the cause or the result of extensive tissue damage

and disease.

Some other observations and recommendations in the wide-ranging report are as

follows:

A simple, rapid, and reliable diagnostic test for use in the field and at the

patient's bedside is urgently needed.

Research is needed to determine what makes children and young adults

especially vulnerable to infection.

Recent serologic studies have shown very little evidence of asymptomatic or

mild H5N1 infections in humans. All healthcare workers studied in Thailand

tested negative, and samples submitted from Djibouti, Nigeria, Kazakhstan, and

Mongolia for testing at the US Centers for Disease Control and Prevention were

all negative. However, some family members of patients in Vietnam tested

positive.

Studies are needed to determine if a genetic predisposition increases the

risk of human infection or of human-to-human transmission among blood relatives.

Resistance to the first-choice antiviral drug, oseltamivir, has been seen in

a few patients, but studies show a low rate of oseltamivir-resistance mutations

in H5N1 viruses in birds. Resistance to amantadine, the second-choice antiviral,

varies among H5N1 strains.

Mallard ducks are now seen as the leading vectors in the geographical spread

of H5N1; mute swans are hghly susceptible to the disease but probably don't

spread it.

Regarding poultry outbreaks in China, " the situation is severe and not yet

fully under control, " and vaccination of the entire poultry population is

needed.

To control H5N1 disease in poultry, vaccination, coupled with appropriate

monitoring, should be used when culling is impracticable.

Scientists who track the disease in ducks should adjust their sampling

procedures to reflect that ducks now shed more virus in their respiratory

secretions than in feces.

The experts' warning against stockpiling of H5N1 vaccines was hailed by

infectious disease expert T. Osterholm, PhD, MPH, as appropriate advice

in view of the virus's genetic variability.

" I think this report will result in a pause in what I think has been a recent

epidemic of vaccine results by press release, " said Osterholm, director of the

University of Minnesota Center for Infectious Disease Research and Policy,

publisher of the CIDRAP Web site.

He also said the report makes clear that the risk of a severe pandemic like

that of 1918 still exists. " Some have suggested that talking about any kind of

pandemic other than [the moderate pandemic of] 1957 or 1968 was tantamount to

scaremongering, " but the report makes clear that from a virologic standpoint,

the H5N1 virus could remain highly deadly while evolving into a pandemic strain,

he said.

" This is a really thoughtful report, and it adds a tremendous amount to the

ongoing discussion, " Osterholm said.

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WHO report calls H5N1 vaccine stockpiling premature

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