The National Advisory Committee on Immunization (NACI), which makes recommendations for the use of vaccines for patients in Canada, released an updated statement for the 2026-2027 influenza season.

NACI reaffirmed its guidance that the influenza vaccine be offered annually to anyone aged 6 months or older, except to those who cannot receive the vaccine because of medical reasons such as an allergy to a vaccine ingredient.

The key changes in the recommendations include the inclusion of new evidence on the optimal timing of seasonal influenza vaccination. This section considers the seasonality of flu activity across Canada and the intraseasonal waning of influenza vaccine-induced immunity.

The current evidence is “insufficient” to establish optimal timing for specific populations, so vaccination in early fall remains the best way to provide “sustained protection” throughout the season, according to the statement.

The statement also includes updated guidance on seasonal influenza vaccination in the context of avian influenza.

“Although seasonal influenza vaccines do not protect against avian influenza A (H5N1) viruses, they may mitigate the severity of seasonal influenza and reduce the risk of coinfection with seasonal and avian influenza strains,” according to the statement. As a result, influenza vaccination is “particularly important” for individuals who are at higher risk for exposure to avian flu viruses.

Waning Immunity and Optimal Timing

The peak of the flu season is unpredictable, so the best time to receive the flu vaccine remains early fall, shortly after the vaccines are available, Matthew S. Miller, PhD, professor of biochemistry and biomedical sciences at McMaster University in Hamilton, Ontario, told Medscape News Canada.

“Failing to get vaccinated early creates increased risk of becoming infected before vaccination or before protective immune responses can be generated,” he said, pointing out that it takes a couple of weeks after vaccination for the immune system to generate protective immunity.

For vulnerable individuals, “as soon as you can” is the best approach to vaccination, Brian Ward, MD, professor of medicine at McGill University in Montreal, agreed. Patients with a low risk for flu complications, however, can choose to wait until the flu is “in the news,” but this is an individual choice.

Each flu season is different, which makes it challenging to shift recommendations ahead of time, Ward emphasized. For example, “some [seasons] start early, and some drag on,” he said, while “some are dominated by A strains early in the season, and B strains often come later.”

Overall, “while we recognize that immunity from influenza vaccination wanes, it still offers protection for 6 months or more and therefore provides protection for most of the respiratory season,” said Jia Hu, MD, interim medical director of Immunization Programs and Vaccine Preventable Diseases Service at the BC Centre for Disease Control in Vancouver.

“As a result, neither NACI nor other immunization advisory organizations recommend different approaches — such as a midseason booster — when it comes to influenza vaccination,” he added.

Randomized controlled trials could provide additional evidence on changing the timing of immunization or the number of doses, said Miller. But “it would be challenging logistically and from a resources perspective to require more than one dose during a single season,” he said.

Coordinating Multiple Vaccinations

“We generally don’t recommend different timing for different groups of people,” said Hu. “However, it is not feasible to immunize an entire population all at once. So, in British Columbia, we offer the vaccine earlier for some groups at particularly high risk of severe influenza, such as those living in long-term care homes.”

The recommendation for adults remains a single dose in early fall, Ward emphasized. “The efficacy of a second dose of the same vaccine in a prolonged flu season has never been well studied,” he said, “so [a second dose] isn’t recommended…even if [flu] cases are still actively happening very late in the season.”

But “the one exception to this is young children [6 months to less than 9 years of age], who are recommended to receive two doses the first time they receive a seasonal influenza vaccine. But that has been a longstanding recommendation,” Miller pointed out.

Influenza and COVID vaccines are updated and offered annually. The respiratory syncytial virus vaccine provides protection in older adults for at least 2 years, and it is not known whether additional doses are helpful.

“These vaccines can be given together along with the flu shot if they are indicated for someone (or at any time before or after the flu shot),” said Ward.

This approach is also helpful from a “programmatic perspective and for patient convenience,” Hu pointed out.

But given that “seasonal waves of COVID remain somewhat unpredictable and misaligned with peak influenza season, it raises questions about whether coordinating timing of influenza and COVID vaccines is [always] practical,” said Miller.

Miller, Ward, and Hu reported no relevant financial relationships.