10/13/2010 08:43 am ET Updated Nov 17, 2011

Why You Shouldn't Mix Flu Shots With Other Vaccines

It's that time of year again. No, not autumn, when all the leaves turn to beautiful shades of red and yellow. (That doesn't happen in southern California, where I live, anyway.) No, not postseason baseball showdowns. (My Angels are out of it this year.) And no, not the new fall television line-up of cop shows and medical dramas. (My wife is a fan, but I'm still waiting for a new "Star Trek" series to come out.)

I'm talking flu shots. Every October the new flu shots come out, people panic that this may be the worst flu season ever, and everyone scrambles to get injected. I won't bore you with all the pros and cons of whether or not you should get a flu shot. I want to focus on making sure those of you who get one are doing so in the safest manner possible.

Make sure you get the flu shot without any other simultaneous vaccines. Why? Because flu shots have not been studied for safety when simultaneously given with any other vaccines. How do I know this? It's written in every single flu shot product insert. Go to section 7.1 for most brands of the flu vaccine and you will find a version of the following statement: "There are no data to assess the concomitant administration of [the flu shot] with other vaccines." In plain English: Scientists haven't studied what the side effects might be when the flu shot is given at the same time as any other vaccines. Some brands don't have a section 7 and don't make any mention of safety research with other vaccines.

One particularly severe reaction that has been reported after flu vaccines as well as some other vaccines is Guillain-Barre Syndrome, which results in temporary paralysis. So, I would think that at the bare minimum, the Centers for Disease Control (CDC) would want to make sure that the grouping of any vaccines that are suspected of being able to cause this reaction isn't more likely to trigger a GBS reaction compared to when such vaccines are given alone.

The only exception to this lack of research is Flumist (the live-virus nasal spray). It was studied simultaneously with MMR and chicken pox vaccines in a group of 1,245 infants (but not children), but it wasn't studied with any of the myriad of other vaccines that an infant or child might receive on the same day.

This flu shot warning is especially true for infants, who could be due for as many as six other vaccines at a checkup. Bring your baby back another month for the flu shot. Five-year-olds will usually get four other vaccines at a check-up. Come back another month for the flu shot. It seems like a no-brainer to me. However, the CDC is so worried that getting off schedule is such a clear and present danger not only to each infant but to society as a whole that it recommends that the flu vaccine be mixed in with any or all other vaccines -- as though a one-month delay in any vaccine were going to matter.

As a pediatrician, I give vaccines in my office every day. I just like to make sure I'm doing it safely. And this complete lack of safety research really leaves me speechless. Fortunately, I can still type this warning for you all. Because flu shots have not been studied with other vaccines, I won't pair them up with any other shots until I see some safety data.

You can check through the flu vaccine product inserts yourself here.

Robert W. Sears, MD, FAAP is a pediatrician and the author of "The Vaccine Book."