Now, I’m no antivaxxer as a general rule. In fact, I’m very PRO-vaccine. And as I’m coming up on 50, and have had chickenpox as a kid (at age 11), I’ve been thinking about getting an anti-shingles vaccine at my next doctor’s appointment (the vaccine is intended for adults over 50; here in Ontario, you can get it for free if you’re 65-70 years old). But now I’m thinking twice about getting it at all, because this news is worrisome:
Zostavax is a live-virus vaccine, and therein lies the danger associated with it. Killed-virus vaccines are generally safer; they teach the immune system to recognize a disease-causing virus by its outer coating, so that the body clears it up before it ever has a chance to take root and cause illness. Killed-virus vaccines use only dead viruses, so there is virtually no risk of illness from getting one (unless the virus is improperly killed, as in the Cutter incident during the early days of production of the Salk polio vaccine, which resulted in an outbreak of the disease the vaccine was designed to combat). However, because the virus cannot replicate, and the immune system may lose the ability to recognize them over time, killed-virus vaccines require boosters to keep the patient immnunized.
Whenever possible, live-virus vaccines are used, because their effects last longer, meaning fewer or no boosters are required. Such is the case with vaccines against the Varicella-Zoster virus, which causes both chickenpox and shingles. The virus has to be weakened (attenuated), rather than killed, for the vaccine to be able to work. When done properly, this might result in a very mild illness following injection, or none at all (usually, none). Some patients with compromised immune systems are unable to receive such vaccines at all, so herd immunity is important in order to protect them. (Get your shots, healthy people — and keep your boosters up to date, too!)
The danger with using attenuated virus vaccines is that the virus used can revert to virulence unexpectedly after generations of relative weakness in human hosts. When that happens, you get full-blown cases of the very illness the vaccine was meant to prevent. That appears to have happened with Zostavax. In one recent case, the vaccine caused death, and that was enough for Australian health authorities to put out a warning on it. Meanwhile, in Pennsylvania, a court case was tossed out on statute-of-limitations grounds.
So what does this mean for regular folks? Well, for those who’ve had the vaccine and suffered no harm, no need to do anything; you’re in the clear. Those who haven’t had it yet? Wait and see, and before you decide to get one, talk with your doctor. Maybe a safer version will come out; maybe the batch that caused the trouble will be recalled and disposed of in the meantime, and future batches will be safe.
I know one thing that won’t be on my to-do list for my next medical visit, though.
