Leaves are falling and public health officials in cities across Canada are announcing the start of flu vaccination campaigns.

Here are some answers to perennial questions surrounding flu vaccines.

The last time I had a flu shot, it gave me the flu.

While the flu shot may give you a sore arm, it can't actually give you the flu, the U.S. Centers for Disease Control and Prevention explains. That's because it's made from a dead form of the virus and such types of vaccines can't give you the infection.

When people think they have come down with flu after getting the shot, doctors say they're either sick with something else like a cold (there's no vaccine for the common cold) or they were already incubating flu. Some people may experience minor discomforts such as headache or sore throat that last for a day or two as the vaccine kicks in.

It takes about two weeks after vaccination for our bodies to produce antibodies that protect against flu infection, the CDC says.

The nasal vaccine, FluMist, contains live flu virus ("live attenuated influenza vaccine") that is engineered to remove the parts of the virus that make people sick. In Canada, it is authorized for use from 2 to 59 years of age except when contraindicated, such as for those with immune compromising conditions, the National Advisory Committee on Immunization says. Provincial and territorial health plans may not cover the cost.

I never get sick so I don't need a flu shot.

Even if you don't get sick you could be a carrier. You may have the flu virus without showing symptoms and infect others. Otherwise, most healthy adults may be able to infect other people beginning one day before symptoms develop and up to five to seven days after becoming sick, the CDC says. Children may pass the virus for longer than seven days, the U.S agency says.

The European Centre for Disease Prevention and Control adds "infectiousness rises steeply" when the person starts to feel unwell.

Flu shots don't work.

A 2012 review of 10 randomized trials concluded the standard, injectable flu vaccine protects healthy adults aged 18 to 64 at a rate of about 59 per cent. Michael Osterholm, an infectious disease expert at the University of Minnesota was the report's lead author.

Flu vaccines don't work on children.

Osterholm's review concluded that the nasal spray containing live attenuated influenza vaccine protects children aged six months to seven years at a rate of about 83 per cent. The CDC has also reviewed studies on how well flu vaccines protect children, citing estimates from 66 per cent to 77 per cent.

People with egg allergies can't be vaccinated.

Canada's National Advisory Committee on Immunization concluded most egg-allergic individuals may be vaccinated against influenza using the traditional vaccine with conditions. Anyone who has a severe allergy to eggs, chicken, or any other part of the vaccine should talk to a doctor first, HealthLink BC advises.

Pregnant women can't be immunized against influenza.

In fact, Canada's National Advisory Committee on Immunization includes healthy pregnant women in its priority list, saying the risk of influenza-related hospitalization is higher in the third than the second trimester.