AS ANTHRAX keeps turning up in yet more US government offices, suspicions are
growing that its source is American
(see 鈥淭he secret is out鈥�).
But wherever it comes from,
postal workers seem to be most at risk. And worryingly, it remains unclear
whether the country鈥檚 ageing vaccine can help鈥攁nd how new and safer
vaccines against such a rare disease can ever be tested and approved.
Clean-up workers may be vaccinated, and health authorities are also
considering vaccinating postal workers thought to be especially vulnerable. But
who is at risk? More undiscovered, contaminated letters could still be out
there. Or anthrax that leaked from the letters already found could be travelling
between post offices on other mail it came into contact with.
The Centers for Disease Control and Prevention in Atlanta says this is
unlikely as anthrax particles cling tightly to surfaces once they鈥檝e been
deposited. It is not clear, however, whether this applies to spores that have
been subjected to a weaponisation process. And as symptoms can take 60 days to
appear, it could be a while before the extent of the health risk becomes
clear.
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The decision the health authorities face is complicated by the fact that the
vaccine is in short supply. The US, Canada and Britain have been vaccinating
soldiers against anthrax since 1997. But in 1998, persistent problems with
quality control halted production at the only US manufacturer, BioPort of
Lansing, Michigan. It will not restart until well into next year at the
earliest. Only 13,000 doses are reportedly available, while 10,000 people in
Washington alone are considered at enough risk of exposure to be given
antibiotics.
If the vaccine wasn鈥檛 in such short supply, it might make sense to give it to
all these people. Antibiotics kill only growing bacteria. Any lingering spores
can cause a relapse after treatment ends, and the CDC approves use of the
vaccine to prevent this.
And there鈥檚 another reason to use the vaccine. In June, at a conference in
Annapolis, Maryland, Lance Price of Northern Arizona University in Flagstaff
reported that it is surprisingly easy to induce resistance to the antibiotic
ciprofloxacin (Cipro) in anthrax. That, in addition to Cipro鈥檚 side effects, may
be one reason the CDC last week recommended switching exposed people to
doxycycline.
But is it not just supplies of the vaccine that are a headache for health
authorities. Its safety is also being questioned. Military personnel have faced
court martial rather than submit to compulsory anthrax jabs, and some who blame
the vaccine for causing debilitating disease launched a lawsuit against BioPort
last month.
The problem is that the licensed US anthrax vaccine, like the similar British
one, is an antique, dating from the 1950s. Both are made from the liquid medium
in which cultures of non-pathogenic anthrax have been grown. After the bacteria
have been filtered out, the medium, which contains various amounts of anthrax
proteins, is mixed with aluminium compounds that help elicit an immune
response.
Researchers at the Annapolis conference reported that it is not even clear
exactly what the vaccines contain, and blamed the complex blend for their
relatively high rate of side effects. After the military鈥檚 bruising experience,
any vaccinations for postal workers will probably be voluntary.
Finally, it is not even clear whether the US vaccine protects against
respiratory anthrax. In a 1960s study of its effectiveness鈥攖he only one so
far鈥攏o vaccinated workers in woollen mills got inhalation anthrax, while
five unvaccinated ones did. But there were too few cases for the study to be
definitive, researchers admit.
Studies in guinea pigs suggest the vaccine is not 100 per cent effective,
especially against the virulent Ames strain used in the attacks. However, the
only primate study so far found all vaccinated rhesus macaques did become immune
to inhaled Ames spores.
New vaccines are showing promise. Live, weakened anthrax makes more effective
vaccines than isolated proteins, at least in animals. In Russia, where people
still get anthrax from livestock, a live vaccine is used, though so far the
small risk of the vaccine itself causing disease has prevented its use in the
West. In pursuit of a safer vaccine, both the Pasteur Institute in Paris and the
US Army are testing genetically engineered forms of weakened anthrax.
Britain鈥檚 Chemical and Biological Defence Establishment at Porton Down is
developing a pure protein vaccine by genetically engineering E. coli to
make a component of anthrax toxin called protective antigen
(快猫短视频, 27 October, p 7).
And a group at Ohio State University in
Columbus has developed DNA vaccines coding for protective antigen or another
toxin component, or both. In June, it reported that all protect mice.
But for any of these vaccines to be approved, they must be shown to be
effective at preventing anthrax in people. And since the natural disease is
extremely rare, it is impossible to meet the normal legal standard, which is to
give a potential vaccine to some people to see if it works.
The US Food and Drug Administration pledged in 1999 that it would devise new
rules to enable vaccines to be developed for threats such as anthrax. These
would combine tests in primates with measurements of the immune reaction in
humans to establish if they were likely to be effective. But these rules have
yet to emerge. Nor do we yet know which of the various kinds of immune reaction
is the key to protecting against anthrax.
