Date: Wed 20 Dec 2000 15:03:10 -0500
From: ProMED-mail <promed@promedmail.org>
Source: Milwaukee Journal Sentinel, 20 Dec 2000 [edited]
<http://www.jsonline.com/alive/news/dec00/flu20121900.asp>
The influenza virus detected in Wisconsin and around the country this
winter is substantially different from the strain that has circulated in
recent years, and few people will be immune to it unless they get a flu
shot, health officials warn. The flu season is just getting started here
and nationwide, and most of the cases sub-typed so far are A-New Caledonia,
which differs [substantially] from the A-Sydney strain that has dominated
the last 3 influenza seasons.
In Milwaukee, the City Health Department's Chief Virologist, Gerald Sedmak,
has been testing blood samples for influenza virus antibodies and says the
tests suggest that only 12% of people will have enough immunity from
previous vaccines or influenza [infection] to protect them [against] A-New
Caledonia. "Very few adults have any protective levels of antibodies, or
antibodies at all, to this virus [subtype]," he said. "There is a large
susceptible population." That means it's even more important for people to
get flu shots this year.
Pete Shult, Chief Virologist at the Wisconsin State Laboratory of Hygiene,
said that the influenza virus that was circulating at the end of the last
flu season, and was incorporated into this year's vaccine, "has changed
enough that it is capable of infecting people" who already have had
A-Sydney. "If you were vaccinated last year, you still have to get
vaccinated this year," he said.
In a typical influenza season, about 10% to 15% of adults become infected
with the virus; 25% to 30% during a major year. [At least] 2 factors
determine the severity of an influenza season: the virulence or infective
potential of the virus itself; and how much of the population already has
antibodies to it, a factor known as herd immunity. Such immunity can be
acquired from a vaccine or naturally, from [a previous infection].
Sedmak has been doing herd immunity studies for many years. Tests on 175
blood samples in the past few months suggest that herd immunity is much
lower for A-New Caledonia than other [influenza virus strains which have
circulated] in the recent past. For example, 95% of the population has
some antibodies to A-Sydney and 55% has levels considered to be protective,
he said.
Nationwide, influenza cases and deaths remain below annual epidemic
threshold levels, according to the Centers for Disease Control and
Prevention (CDC). Activity in Wisconsin has been light, too, but the
season typically peaks in January. In Milwaukee, 3 cases have been
confirmed. It's important to be vaccinated soon, because it takes one to 2
weeks for sufficient antibodies to form after getting a flu shot.
This year's influenza vaccine continues the B-Beijing strain used
previously plus 2 new A strains: A-Moscow and A-New Caledonia. Influenza
can occur even after vaccination, though it's usually far less severe than
it would be without vaccination. The vaccine prevents illness in 70% to
90% of healthy people younger than 65, and it prevents hospitalization in
30% to 70% of older people, depending on their general health, according to
the CDC.
[Byline: Marilynn Marchione]
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