WHO advises total makeover for 2008-09 flu vaccine

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WHO advises total makeover for 2008-09 flu vaccine

Roos * News Editor

Feb 14, 2008 (CIDRAP News) – The World Health Organization (WHO) today

reported evidence of a less-than-satisfactory match between all three

components of this season's influenza vaccine and the flu strains

currently making people sick.

Last week US health officials reported mismatches between the

influenza A/H3N2 and influenza B components of this year's vaccine and

the circulating H3N2 and B strains. Today the WHO reported that the

majority of recent H1N1 virus isolates globally have not matched well

with the H1N1 component of the vaccine.

As a result, the WHO today recommended replacing all three components

in next year's flu vaccine for the northern hemisphere.

H1N1 is the flu subtype that has begun to show resistance to the

antiviral drug oseltamivir (Tamiflu), one of the two neuraminidase

inhibitors recommended for flu patients. In a separate update today,

the WHO said H1N1 viruses with a resistance mutation have been found

in 18 of 37 countries where the viruses have been analyzed. The

mutation was observed in 14% of the isolates studied, including 8% of

those in the United States.

Each February the WHO assesses the flu virus strains in circulation

before picking the strains for the next northern hemisphere flu

season. It takes about 6 months for vaccine manufacturers to grow the

viruses in chicken eggs and formulate them into trivalent

(three-strain) vaccines. Changing one or two strains is not unusual,

but replacing all three is less common.

The WHO recommended the following for next season's vaccine:

* For the H1N1 component, a strain similar to A/Brisbane/59/2007,

replacing A/ Islands/3/2006

* For the H3N2 component, a strain similar to A/Brisbane/10/2007,

replacing A/Wisconsin/67/2005

* For the B component, a strain similar to B/Florida/4/2006,

replacing B/Malaysia 2506/2004

The Brisbane strains of H1N1 and H3N2 will be used in this year's

vaccine for the southern hemisphere, where the flu season runs from

May through October, according to the WHO.

The agency said H1N1 viruses were the predominant flu subtype in most

parts of the northern hemisphere from September through January,

though flu activity in that period was generally low in comparison

with the same interval in recent years.

While some H1N1 viruses analyzed this season were similar to the

Islands strain used in the vaccine, " the majority of recent

isolates were distinguishable from the vaccine virus and antigenically

similar to A/Brisbane/59/2007, " the WHO report states.

The report says that in lab tests, serum samples from people immunized

with this year's vaccine generated a lower antibody response to recent

H1N1 isolates than to the Islands H1N1 strain used in the

vaccine. For example, 93% of adult samples generated a significant

antibody response (titre of 40 or higher) to the Islands

strain, but only 59% of adult samples generated a similar response to

recent isolates. However, the WHO offered no comment on the clinical

significance of the findings.

The US Centers for Disease Control and Prevention (CDC) reported last

week that 46 of 53 H3N2 viruses it had tested through Jan 26 were

similar to A/Brisbane/10/2007, which evolved from the Wisconsin strain

used in the vaccine. The CDC also said 40 of 43 influenza B viruses

tested belonged to the Yamagata lineage, not the lineage

represented by the Malaysia strain used in the vaccine. (A CDC update

today, covering the period through Feb 2, did not list any new numbers

for the circulating strains.)

The CDC has not cited a problem with the H1N1 component of the

vaccine. The agency did not return a call today in time to comment on

the WHO report, but it has scheduled a briefing tomorrow on the flu

season.

As recently as Jan 31, the WHO, in reporting on the resistance of H1N1

viruses to oseltamivir, said the H1N1 strain used in this season's

vaccine was well-matched to the circulating strains.

In today's update on the oseltamivir resistance problem, the WHO said

237 (14%) of 1,703 H1N1 viruses tested so far had the mutation

conferring resistance. Resistance rates are highest in Norway (66% of

isolates), France (40%), and Luxembourg (25%).

http://www.cidrap.umn.edu/cidrap/content/influenza/general/news/feb1408vaccine-j\

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