TORONTO -- Saving the flu shot for âwhen you really need itâ is like playing Russian roulette, says one Ontario researcher who compared more than two dozen studies about âserial vaccinations.â
Annual flu shots remain the recommendation among doctors, despite growing evidence that repeated vaccination may weaken the bodyâs 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.
âSome protection is better than no protection,â said Kwong, who in January published a review of 26 studies in the with Toronto colleagues and researchers in Hong Kong.
âGetting the influenza vaccine repeatedly, in general, is not harmful,â he told CTVNews.ca. âItâs just that it may work a little bit less well.â
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 âserial vaccinationâ 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 yearâs vaccine is similar to last yearâs vaccine, the antibodies you developed from last yearâs vaccine may âneutralize this yearâs vaccine,â explained Kwong. And then, if the circulating viruses this year are different from last yearâs vaccine, you may not get any protection from this yearâs vaccine.
But what are you supposed to do with that information? Thatâs 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 didnât get it last year and the question is still whether or not to get it this year. No one can âun-get the one from last year,â he said, so attempting to self-impose a bi-annual of tri-annual flu shot policy on yourself is a risk.
âHow do you know when youâre really going to need it? Itâs a little bit of Russian roulette. Thatâs why the recommendation is just to get it every year,â he said.
âEven if youâre getting less protection thatâs better than no protection.â
Limited data
The widespread availability of flu shots everywhere from pharmacies to workplaces, and the reliability of a personâs own recollection of their history, have limited the data available to researchers. That reality means public health recommendations remain intact.
âFrom the policy perspective, should we tell people to get vaccinated every year or alternating years or once every three years? We donât really know,â said Kwong.
âWhat weâre saying is probably itâs best just to get vaccinated every year for the most part.â