Nov. 23 (Bloomberg) -- Canadian doctors should hold off on using a batch of GlaxoSmithKline Plc’s swine flu vaccine while the company probes reports of higher-than-expected occurrences of a side effect known as anaphylaxis, a spokeswoman for the U.K. drugmaker said today.

The batch of 172,000 doses of Arepanrix was linked to more cases of acute allergic reactions, including swollen tongues, throats and respiratory distress, than is expected, spokeswoman Gwenan White said in a telephone interview. Typically, about 1 person in 100,000 will suffer such a reaction, she said.

“It is a low rate, only marginally greater than what we’d expect,” according to White, who said she couldn’t confirm the exact number. “It doesn’t have any impact at all on the other vaccine they have received and can continue to administer.”

About 65 million people worldwide have been vaccinated with swine flu vaccine, the World Health Organization said in a statement last week. Evidence so far indicates that shots for the pandemic H1N1 influenza are as safe as those for seasonal flu, the Geneva-based United Nations health agency said.

Nearly 80 million doses of vaccine have been distributed in 40 countries with pandemic immunization campaigns under way, the agency said. Other companies manufacturing vaccine include Novartis AG, Baxter International Inc., CSL Ltd., Sanofi-Aventis SA and AstraZeneca Plc.

Sole Supplier

Glaxo, the sole supplier of swine flu shots to Canada, has shipped 7.5 million doses to the country, White said. Canadian health officials received higher-than-expected reports of anaphylaxis in patients getting the shot from one particular batch, which the company has now held, she said. The reactions haven’t been confirmed and are being investigated by health authorities, she said.

Glaxo, based in London, sent a letter to Canadian doctors and health-care professionals to ensure they were aware of the situation, she said.

“It’s always a bit nerve-wracking when you see such a huge number of vaccines rolled out in such a short amount of time,” said Navid Malik, an analyst at Matrix Corporate Capital, in an interview. “This is unknown territory. Until I see all the information I won’t be completely relaxed about it, but you have to kind of accept this is a one-off.” He recommends buying Glaxo shares.

Food Allergies

Health professionals should ask people if they have any food allergies before administering the vaccine since it is manufactured using eggs, said White. If they do have a severe reaction to the injection, doctors should have medicines including steroids and antihistamines ready to treat the patient, she said.

The most common side effects of the vaccine are swelling, redness and pain at the spot of the injection, all of which resolve quickly, the WHO said. Fevers, headaches, fatigue and muscle aches have also been reported, with most improving within two days.

Fewer than 10 patients may have developed Guillain-Barre syndrome, an immune system reaction that was linked to a swine flu vaccine given in the U.S. decades ago, and all recovered, the WHO said. The cases are being investigated to see if the illness was a random event, or connected to the vaccination, the agency said.

There haven’t been any deaths conclusively linked to the injection, the agency said.

To contact the reporter on this story: Michelle Fay Cortez in London at mcortez@bloomberg.net

Last Updated: November 23, 2009 12:14 EST