2018-01-09 from cbc.ca

It's peak flu season in many parts of Canada.  A serious strain of the virus is sending many Canadians to doctors' offices and to hospitals, yet again raising questions about the benefits of the annual flu shot.  A study published in the Canadian Medical Association Journal provides some welcome news.  

The value of  repeated flu shots in older adults is that doing so reduces the severity of the illness.  That's according to a study by a team of researchers in Spain.  They looked at what happened to adults age 65 and up who got vaccinated each year for four years ending in the 2014-2015 flu season. Compared to those who didn't receive regular flu shots, those who rolled up their sleeves without fail every year got just as many cases of flu.  But the cases of flu they got were milder ones. 

Those who got vaccines more often were half as likely to have a severe case of the flu. They were also less likely to be admitted to hospital with the flu, and less likely to die of it.   

You may be confused by the results, but veteran flu watchers I spoke with say they aren't.  It caught me somewhat off guard given the questions raised each year about the effectiveness of the annual flu shot.  This winter, flu watchers are quite concerned because the strain of influenza in Canada this winter is almost identical to the H3N2 strain that predominated in Australia last year. 

Australia's 2017 flu season was between June and August of last year, which corresponds to winter in the southern hemisphere. 

Last year, Australia had more than 217,000 confirmed cases of flu, double the previous record of 100,000 cases reported in 2015.  Unfortunately, the vaccine used in Australia was only 10 per cent effective, prompting fears that the same fate awaits Canada. 

I stress that we don't yet know for sure if this year's flu shot will turn out to be just 10 per cent effective, but that won't surprise flu watchers in Canada.

It seems to be a constant and often unmet challenge for vaccine experts to make a seasonal flu shot that is consistently effective.  There are several reasons for this.

Prevailing flu viruses mutate rapidly. It can take less time for a virus to mutate than it does for scientists to manufacture a vaccine.  It's not for lack of trying.  More than 100 national influenza centres in over 100 countries conduct year-round surveillance of influenza. Twice a year, the World Health Organization (WHO) consults with those laboratories to recommend which strains to put in the flu shot. For this year's flu season, the meetings took place in February 2017.  For the vaccine used in Australia, the meetings took place in September 2016. 

After the WHO announces its recommendations, each country makes a final decision on what to include in its own seasonal flu shot. 

To manufacture the vaccine, you need a good vaccine virus. These must be isolated and grown in chicken eggs, tested and available in time to ramp up production. Occasionally, a suitable vaccine virus can't be identified or developed in time for the flu season.  It takes at least six months to produce large quantities of influenza vaccine. 

If you're still with me, you may be wondering how getting a mediocre seasonal flu shot every year confers additional benefit.  It turns out that vaccines have two ways of killing nasty flu bugs  The first (and most well known) is that the vaccine induces the body's immune system to make antibodies against the virus.  Still, a vaccine that is only 10 per cent effective produces antibodies that don't do a good job of attacking the flu virus.

Read more here