It's that time of year when seniors in long term care facilities, and those with underlying conditions to queue up for their annual flu shot. A month later, everyone else will be encouraged to follow suit.

Though the 2010-2011 flu season was mild overall (CCDR report), some areas (including the Greater Toronto Area) saw seniors and nursing homes briefly, though significantly, affected by the flu outbreaks. Many of these outbreaks occurred despite the fact that these populations, in addition to those who care for them, were well covered by the flu shot.  And last year’s flu strain had been seen in previous years, and was a good match with the strains that ended up circulating. In summary, recent events suggest that annual flu shot campaigns are not as effective as had been hoped when the annual ritual started 20 years ago. There is a need for a new approach.

While this year’s flu shot contains the same strains as last year’s shot, we don’t yet know what strains are in store for the coming season – the same or possibly a drifted strain of what circulated last year. If the strain is different from last year’s, we may be in for a worse flu season.

Target the "Herd" Better?

Given that the most vulnerable do not get optimal protection from the flu shot, it may be wiser to target those who spend time with this group (the "herd"). The "herd" would of course include healthcare providers such as myself fall into this category.  Another approach, published by Canadian researchers in JAMA suggests that vaccinating more children from age 3 to 15 might indirectly protect older adults and isolated communities from disease, as community flu outbreaks typically begin in school-aged children.

New Vaccine Delivery Systems?

The “tried and true” killed virus flu shot is still available and is, by and large, a safe vaccine. However, we are increasingly aware that the vulnerable do not have an enduring protection from it, as discussed in a recent analysis in Lancet Infectious Diseases. Even if the vaccine is a perfect match the flu strains that subsequently come through (last year is a good example of this), this caveat applies. So,  a few approaches are now being used to help boost protection in the vulnerable groups:

a) give the vaccine into the skin, rather than into the muscle (Intanza®) or;

b) add an “adjuvant” to the vaccine (FluAd ®) – this seems work better in children than in adults though; 
c) give the healthy population a live “weakened” flu vaccination through the nose rather than through an injection, mimicking naturally-acquired infection (FluMist ®). This vaccine is currently proven to work best in children aged six months to seven years.

Depending on the province, some of these new vaccines are being covered by provincial health budgets, though not for the most part. Some specialized programmes in Alberta and Nunavut are implementing FluMist®.

Is FluMist® The Way to Achieving Better “Herd” Immunity?

Any parent would vouch that a nasal spray is a much easier sell to their kids than an injection. Even the reticent adults might more willingly “take the jab” in this new form. Intuitively speaking, a vaccine that is delivered through the same route as how the actual infection is acquired delivers a more enduring protection. According to the National Advisory Committee for Immunization Statement (see The Lancet ), the data suggests that FluMist® works better for children up to seven years of age than does the standard flu shot.

Despite the appealling aspects of FluMist®, which has been available in the United States since 2003, it has not seen widespread adoption there. Here are a few reasons why:

• It can’t be administered to everyone, as it is a live, weakened virus vaccine (unlike the usual seasonal flu vaccine, which has no live components). So the needle-free vaccine itself might cause disease in those at greatest risk for flu complications.
• Pregnant women cannot receive it, again, because it is a live virus vaccine. Similarly, health care providers who work with severely immunocompromised patients (such as bone marrow transplant recipients) are not recommended to get it, lest they unwittingly spread the live vaccine virus to patients.
• It causes mild runny nose more than the flu shot, again because it is a live vaccine that mimics the route of naturally-acquired infection
• Those with severe asthma may experience a worsening of their symptoms if they receive it.
• Its’ component strains still need to be conceived well in advance of flu season; sometimes the guess is bad. Fortunately, the manufacturing time interval is shorter than with inactivated killed flu vaccine, though not short enough to allow for a revision of the strains in the event of something new (e.g. a pandemic due to a significant flu strain drift or shift.
• The vaccine still needs to be given by a doctor, although in Alberta, BC and Nunavut, pharmacists will be permitted to administer it in select circumstances.

Cost: FluMist® is more costly ($70/dose retail price) than the older vaccine, and public coverage for these costs is going to be a matter of debate as cost-effectiveness arguments ensue: would additional lives of the vulnerable indirectly be saved even if every Canadian aged 2 to 59 were to get it? We don't have the scientific evidence yet.

Where Are We Headed?

Flu is here to stay, and last year as “good” as it will get. Routine vaccination of the vulnerable will continue for now, possibly using the newer vaccines that generate a stronger immunity in these folks. But we’ll also see a move towards vaccinating the healthy (health care providers and close contacts) who spend time with the vulnerable, and those who subsequently spread the virus (children age 2 to 15) using more convenient and perhaps more effective vaccines for this population (e.g.  FluMist®). Until we have more effective vaccines available for the entire population to use, the goal of universal immunization may need to be put on hold.