As new human swine flu cases continue to mount, the question of whether we need a vaccine is being asked with a little more fervour.

A vaccine sounds like an easy solution to ensuring that people not yet exposed to the virus won't get infected. But developing such a vaccine is neither simple nor free of risk.

Producing a vaccine would take months - and production can only begin after health authorities release samples of the virus to manufacturers to begin production.

The U.S. Centers for Disease Control and Prevention says it has already taken a sample of the virus from people who fell ill in Mexico and the U.S. They've produced a "seed stock" of a "reference strain" of the virus -- the first stage of any vaccine production process.

"We're about a third of the way" to that goal, Dr. Ruben Donis of the Centers for Disease Control and Prevention told The Associated Press Tuesday.

But as of yet, the World Health Organization and the U.S. Centers for Disease Control in Atlanta are not sure they want to commission a pharmaceutical company to mass-produce a vaccine.

WHO and CDC experts are first trying to decide if a vaccine for the new flu strain is needed. While the virus is spreading, it is causing mostly mild illness, with the notable exception of Mexico. The illness may take care of itself without the need for expensive and sometimes risky vaccine production.

The WHO would only call for mass production of such a vaccine if it strongly believed the world were on the edge of an unstoppable global outbreak.

Public health authorities don't want to jump the gun too quickly, with many remembering the disaster of the mass vaccination program in the U.S. in 1976.

When a swine flu caused an outbreak at Fort Dix in February of that year, the Ford administration panicked. Though only five people have become infected and one person had died, the government decided to order a vaccine.

By October, the vaccine was ready to go. More than 40 million Americans were given the shot in a vaccination program that cost the U.S. government US$135 million -- about $500 million in today's money.

But the pandemic never happened and more than 500 people who got the shot also developed Guillain-Barré syndrome, a neurological disorder that can result in paralysis. By April, more than 30 people had died of the condition. The ensuing lawsuits cost the federal government millions of dollars.

The lesson learned is that that public health authorities should get a vaccine ready for production, but they should also carefully assess the disease situation before pulling the trigger.

For now, vaccine companies, such as Sanofi-Aventis SA, Glaxo, Novartis AG and Baxter International Inc., say they are on standby, waiting for the word.

"Sanofi Pasteur, as the world leading producer of influenza vaccine, is standing ready to assess its capabilities to support public health efforts, should the WHO and other health authorities request support from influenza vaccine manufacturers," said spokesman Pascal Barollier.

But even if vaccine makers were given the word today to starts producing a vaccine, production is a painfully slow, almost archaic process. Flu vaccines must be grown in specially-produced eggs.

Here's how it's done:

• An influenza virus is injected into a fertilized chicken egg 11 days after fertilization.
• The virus accumulates in the embryo, allowing the virus to multiply.
• After several days of incubation, machines open the eggs and harvest the virus.
• The virus is then purified and chemically inactivated to become a vaccine.

The World Health Organization warns it could take four to six months before the first batch of vaccines are available to fight the virus. That means that it wouldn't be until the end of the summer, at the earliest, before Canadians could get the shot.

Experts admit the current vaccine production process is clumsy. There are many better and more efficient methods, such as growing viruses in cells rather than eggs. That involves growing vaccine components in human, monkey, canine, insect, or other cells in enclosed vats. Cell-culture techonology is already being used for vaccines such as polio, hepatitis A, chickenpox and shingles.

Estimates vary as to how much time could be saved with cell-culture production, but experts familiar with both methods say it could shorten the process by at least a month. What's more, cell-culture vaccine production is considered safer and more sanitary and allows manufacturers to increase vaccine production quickly if needed.

But the use of this newer technology in current vaccine production is still a few years away. Until then, Canadians will have to make do with relying on a whole lot of chickens to make the shots that can keep them safe.