Currently, influenza vaccines come in two flavors: nasal and injectable. The nasal vaccine is a live, attenuated vaccine. This means that the virus, while still “alive”, has had its cellular machinery crippled so that it won’t cause a whole body infection. The injectable vaccine is inactivated, or killed. It is wholly incapable of causing infection.
The nasal vaccine is very popular in our office. I guess people get enough shots around here, already. Based on a study which came out today in the NEJM, I may be rethinking how I recommend different vaccines.
This study looked at healthy volunteers aged 18 to 49 years. A very important point is that none of these individuals had a condition for which vaccine was explicitly recommended, i.e. healthcare workers, asthmatics, very old, very young, etc. In this study population, the inactivated, injectable vaccine was clearly better at preventing influenza. It wasn’t even close. Rates of infection were 3.5% for the injectable vaccine, 7% for the nasal vaccine, and 11% for placebo.
This study is important in answering which vaccine young, healthy individuals should receive. Results from other studies looking at outcomes in asthmatics have suggested that the nasal vaccine may actually be more effective at preventing influenza related exacerbations. Clearly, this is an important question that needs more data to make a definitive answer.
I got my flu shot BTW