TORONTO -- Saving the flu shot for 鈥渨hen you really need it鈥� is like playing Russian roulette, says one Ontario researcher who compared more than two dozen studies about 鈥渟erial vaccinations.鈥�
Annual flu shots remain the recommendation among doctors, despite growing evidence that repeated vaccination may weaken the body鈥檚 ability to fight the influenza viruses. That research is no reason to skip out on the shot altogether, said Jeff Kwong, a scientist with ICES and Public Health Ontario.
鈥淪ome protection is better than no protection,鈥� said Kwong, who in January published a review of 26 studies in the with Toronto colleagues and researchers in Hong Kong.
鈥淕etting the influenza vaccine repeatedly, in general, is not harmful,鈥� he told CTVNews.ca. 鈥淚t鈥檚 just that it may work a little bit less well.鈥�
Kwong and fellow researchers are currently working on a new study about the impact of serial vaccinations that takes into account a 10-year history. To date, most studies have only examined effectiveness between two and five years.
Virus mutation
The 鈥渟erial vaccination鈥� question relates to a scientific concept known as the , which theorizes that your last flu shot may interfere with the new flu shot if the vaccines are similar and the current flu strain has mutated more than anticipated.
If this year鈥檚 vaccine is similar to last year鈥檚 vaccine, the antibodies you developed from last year鈥檚 vaccine may 鈥渘eutralize this year鈥檚 vaccine,鈥� explained Kwong. And then, if the circulating viruses this year are different from last year鈥檚 vaccine, you may not get any protection from this year鈥檚 vaccine.
But what are you supposed to do with that information? That鈥檚 where a dangerous game can begin, said Kwong.
Russian roulette
You either got the shot last year and the question is whether or not to get it this year, or you didn鈥檛 get it last year and the question is still whether or not to get it this year. No one can 鈥渦n-get the one from last year,鈥� he said, so attempting to self-impose a bi-annual of tri-annual flu shot policy on yourself is a risk.
鈥淗ow do you know when you鈥檙e really going to need it? It鈥檚 a little bit of Russian roulette. That鈥檚 why the recommendation is just to get it every year,鈥� he said.
鈥淓ven if you鈥檙e getting less protection that鈥檚 better than no protection.鈥�
Limited data
The widespread availability of flu shots everywhere from pharmacies to workplaces, and the reliability of a person鈥檚 own recollection of their history, have limited the data available to researchers. That reality means public health recommendations remain intact.
鈥淔rom the policy perspective, should we tell people to get vaccinated every year or alternating years or once every three years? We don鈥檛 really know,鈥� said Kwong.
鈥淲hat we鈥檙e saying is probably it鈥檚 best just to get vaccinated every year for the most part.鈥�
