Low circulation of the flu over the past two years is a factor, say experts who also fear fewer pandemic measures and reduced vaccinations will increase risks.
The authorization says the vaccine can be given three to six months after a second dose of the primary vaccine series, or the most recent booster shot.
NACI includes recommendation to use one-fifth the usual dose intradermally (off-label) for the second pre-exposure vaccination dose, in times of limited vaccine supply.