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If you went by statements from the pharmaceutical industry, you might be tempted to think it was nearly time to roll up your sleeve for a swine-flu shot.

In the race to produce a pandemic vaccine, several companies have declared themselves front-runners, suggesting that their products are on the verge of being ready.

But are they on the verge of being ready for use? Maybe not just yet.

“I've seen a couple of press releases ... saying ‘By early summer we're going to have something.' They may have something off the production line,” Halifax vaccinologist Scott Halperin says with a chuckle.

Making vaccine and convincing regulatory agencies that the substance is safe to inject into humans are separate matters. That is always the case, but it's especially true when the vaccine in question is to protect against swine flu.

The last time mass vaccination against a swine-flu virus was undertaken, a spike in cases of Guillain Barré syndrome among those vaccinated led U.S. authorities to abandon the program.

It is still not known why that 1976 vaccine seemed to trigger an elevated number of cases of the paralyzing condition. (The syndrome, which is linked to several natural infections and to some vaccines, generally reverses itself over time.) Does that incident cast a long shadow over discussions about a 2009 swine-flu vaccine?

“Yes, it does,” Dr. Halperin says. “Certainly it makes people plan to monitor very carefully with the new vaccine.”

Seasonal flu shots protect against one strain of influenza B and two of influenza A, including a human subtype that rather confusingly goes by the same name as the swine-flu virus – H1N1. But despite the similarity in names, seasonal flu shots don't offer any protection against the new swine-derived virus.

So this fall, people living in flu-vaccine-using countries may face a situation in which they are urged to get a seasonal flu shot, on the assumption that those viruses will still be circulating, and also a pandemic flu shot to protect against the new H1N1 virus, if a decision is made to deploy that vaccine.

But there are lots of questions regulators such as Health Canada and the U.S. Food and Drug Administration will want answered before they give the go-ahead for pandemic H1N1 vaccines. And the clinical trials needed to get those answers take time.

“We can't hasten the time frame that you need to do clinical trials to get the fundamental, basic information that you generally need,” says Anthony Fauci, head of the U.S. National Institute for Allergy and Infectious Diseases.

NIAID is one of the U.S. National Institutes of Health. It will be working with the FDA and with U.S.-licensed flu-vaccine manufacturers to determine research needs for the new vaccine. The aim is to fill data gaps that individual companies won't or can't undertake to plug.

Those include looking at vaccine safety in potentially more vulnerable groups such as infants, people whose immune systems are compromised, and pregnant women.

Another question NIAID may try to answer is whether it would be possible to compress the interval between two swine-flu shots if, as suspected, two shots are needed.

Companies will probably test a regime that would see two shots given with a 21- or 28-day interval. But if the pandemic starts to worsen and it appears waiting that long would be unwise, could the same effect be achieved with two shots given closer together? Companies probably won't do that research, but NIAID could, Dr. Fauci says.

The types of studies companies will need to do are the ones that answer the core questions about a vaccine: Is it safe to use in humans? Does it elicit an immune response – rising levels of antibodies – that would suggest it will be protective? What size of dose, and how many doses, does it take to do so?

Getting those answers means weeks of work by individual companies. They'll start by injecting their products into animals, then into small numbers of human volunteers to determine that the vaccines are safe.

Once that is clear, larger trials will be needed to determine how large a dose people need to get a good immune response. That could take a couple of months, says an expert who has done many trials on flu vaccine.

“No matter how quickly you enroll the subjects in the study, even if everybody was enrolled on the same day, it's still going to take time to get the study done and get the data,” says John Treanor, who teaches at the University of Rochester in northern New York.

That work should answer the question of whether people might get enough protection from a single shot or whether, because this is a new virus for our immune systems, two shots will be required. Experts hope for the former, but suspect the latter.

The industry has years of experience making flu shots and there is a high degree of confidence that a successful swine-flu vaccine can be made. But each flu virus has its own quirks and no one knows yet how well a new vaccine will do at eliciting an immune response in people.

“Until they actually get it and start putting it into some animals and humans, they're not going to know for sure,” says Dr. Halperin, a professor at Dalhousie University and principal investigator of the new influenza research network of the Public Health Agency of Canada. Because seasonal flu shots have to be updated on a regular basis, regulatory agencies have a fast-track process for these vaccines.

As long as nothing about the production of the vaccine changes, vaccines against a new strain or subtype of flu virus can be switched in under an existing licence with minimal additional information required.

That may not be the case here, however.

Some manufacturers – including GlaxoSmithKline Inc., which has Canada's pandemic vaccine contract – have indicated they want to use adjuvants in their vaccines. Adjuvants are boosting chemicals that allow smaller doses to be used, which would speed up the time it takes to make enough vaccine for a country.

But there are no existing flu vaccines in Canada that contain adjuvants, so adding one could require an entirely new licence – and substantially more safety data based on clinical trials.

It is believed Canada will purchase adjuvanted vaccine. But what testing it will require to assure itself of the product's safety isn't currently known.

The Canadian Press has been asking for weeks for an interview with David Butler-Jones, head of the Public Health Agency of Canada, to discuss issues related to the country's pandemic vaccine contract.

Permission for an interview has not been granted by the Prime Minister's office.

However, Health Canada, which regulates vaccines, provided by e-mail some information on what will be expected from manufacturers to license an H1N1 vaccine.

It said companies will be required to submit immunogenicity data – results of clinical trials that show whether the vaccine elicits a sufficiently strong immune response. And vaccine manufacturers are being asked to submit plans for how they will conduct surveillance for adverse events once their vaccines are in wide use.