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WE KNOW they’ve got anthrax. But what else could bioterrorists have in store?
Perhaps the greatest threat is smallpox, a disease officially eradicated in 1980
that can kill with chilling efficiency.

Unlike anthrax, the Variola major virus that causes smallpox is contagious.
It spreads through the air, killing 1 in 3 of the people it infects. That means
a bioterrorist attack could become a worldwide epidemic. Older people vaccinated
before the last jabs were given in 1972 might still have some immunity, but the
rest of us are vulnerable.

Fortunately, the smallpox vaccine not only protects against the disease, it
can also help treat it if given within four days. But little remains in
stock—and what there is may be useless. “We know there are about 90
million doses available,” says Dave Hayman, executive director of communicable
diseases at the World Health Organization. “What we don’t know is what
proportion is active. Most was made 20 years ago.”

While it’s hard to imagine anyone using such an indiscriminate weapon as
smallpox, the possibility can’t be ruled out. Only labs in the US and Russia are
still supposed to have samples. But military-grade smallpox was produced by the
tonne in the Soviet Union during the 1970s and 1980s. Although former Russian
president Boris Yeltsin agreed in 1992 to destroy the stockpile, the fear
remains that some strayed into malevolent hands.

The US only has 15.4 million doses of the vaccine left and just 1 million of
the special forked needles for dispensing it. Yet when a single sporadic case
occurred in Yugoslavia in 1972, 18 million doses of the vaccine were given,
according to Steven Rosenthal, an authority on vaccines at the US Food and Drug
Administration.

But even if enough vaccine was available, health authorities would try to
avoid mass vaccination because of its potentially fatal side effects. They
include skin complications, swelling of the brain and tumours. “The risk of
adverse events is sufficiently high that mass vaccination is not warranted,”
says Gro Harlem Brundtland, director general of the WHO.

The best method of stopping an outbreak remains identifying cases and
isolating them, according to the WHO. Vaccines should be reserved for anyone who
might be infected. But the old stockpiles are almost certainly past their best.
“It’s accepted that the [old] vaccine has a shelf life of just 18 months,” says
Lyndsay Wright of Acambis, a British company that makes the vaccine. “The last
lot was manufactured in 1983, so the entire stockpile might be ineffective.”

The US is checking if its vaccine still works, and if it can be diluted to
make extra doses. Tommy Thompson, the US health secretary, last week also
announced a $509 million programme to buy 300 million more doses of
smallpox vaccine.

Other countries are also restocking, according to Bavarian Nordic, a Danish
biotechnology company in Copenhagen. It says it can supply up to 100 million
doses within as little as 9 months, and is discussing possible orders with “a
number of governments”. It has already tested one of its two smallpox vaccines,
code-named MVA-BN, in 90 healthy volunteers.

Like Edward Jenner’s original vaccine dispensed 200 years ago, Bavarian
Nordic’s and Acambis’s vaccines are based on vaccinia, the cowpox virus. These
days vaccinia is made in living cells grown in a fermenter rather than extracted
from the pustules of calves infected with cowpox.

But how can we be sure these vaccines will work when the disease no longer
occurs? Under the US’s recently announced fast-track approval process for
smallpox vaccines, a vaccine will be given to healthy volunteers, and
researchers will look for specific antibodies shown to protect against smallpox.
But there’s no way to be sure vaccines that pass this test will protect against
the cfSoviet weapons strain.

Unlike in the past, however, there are now potential treatments. A drug
called cidofovir, already made by Gilead Sciences of California to combat eye
infections in people with AIDS, has been shown to protect cells against
smallpox. And James LeDuc of the US Centers for Disease Control has identified
substances far more potent than cidofovir.

We certainly aren’t prepared for a smallpox attack at the moment. But it’s
clear that if health authorities are given the resources, the virus can be
beaten. The challenge for governments will be in maintaining preparedness long
after the memory of the anthrax attacks has faded. Even then, the worry will be
that an attacker will simply choose different bioweapon.