Flu vaccination when travelling between countries.

I really enjoyed the article and podcast on the prevention and treatment of influenza.1

This year the flu was very common in Japan. As a lot of Australian tourists go to Japan for sightseeing and skiing, I wanted to ask:

can travellers have a flu shot in Japan in January or February even if they have had the flu shot in Australia in the autumn of the previous year?

is the flu shot in Australia still effective at preventing influenza in Japan?

do you have any suggestions to prevent bringing the flu virus from Japan to Australia?

Nowadays we see patients with flu all year round. I think one of the causes of this is that people bring the flu virus from the northern hemisphere.

Dominic Dwyer, one of the authors of the article, comments:

There is no doubt that influenza viruses circulate between the northern and southern hemispheres, and travellers contribute to this circulation. This complicates advice to travellers from Australia to Japan, especially during the Japanese winter.

Influenza-specific antibodies induced by the vaccine last for around six months. This means that vaccine administered in April–May before the Australian winter is unlikely to have any significant benefit for people going to the northern hemisphere winter in January–February. It would therefore be reasonable to offer vaccine to Australians travelling to the northern hemisphere in winter assuming the vaccine is available in Australia at this time.

It takes about two weeks for vaccine-induced antibodies to appear, so vaccination on arrival in Japan during winter is unlikely to help most travellers. Advice about personal protection and handwashing during the influenza season is helpful, as is early diagnosis and neuraminidase inhibitor treatment in individuals with an influenza-like illness.