Smoking impairs the immune system in at least a few ways. Before we talk about the ways that smoking impairs immunity, let’s briefly review how the immune system works against flu.

If you were to look inside your nasal cavity, throat, and lungs, you’d see the structure of the cavities, covered by soft tissue called mucosa. The overall name of this area is the respiratory tract. The mucosa has special cells that secrete mucus, which coats the tissue in a thin layer. The mucus itself is full of immune cells, antibodies, and other biochemical and cellular weapons that the body uses to detect and kill pathogens like viruses and bacteria. The outermost cells in the mucosa also have hairlike projections called ‘cilia’ that extend into the mucus layer and beyond. The cilia are very important in fighting infection. Basically, when pathogens get into the respiratory tract, they get a little stuck in the mucus. The cilia are constantly beating and pushing things upward toward the mouth. Imagine millions of little cilia all around the breathing tubes, and other parts of the respiratory tract. We call this system the ‘muco-ciliary elevator’ because it brings stuff up from the lungs and through or sinuses toward the mouth where we can cough it up and clear it. And meanwhile, the immune cells and antibodies in the mucus are already starting to kill the pathogens.

Smoking damages both the immune cells and the muco-ciliary elevator. So it prevents the body from doing what it otherwise knows how to do. In smokers, the body is much less able to clear viruses and bacteria because the immune cells and mucociliary system are not functioning properly. The result is increased rates of flu infection during pandemics and worse symptoms from flu. Smokers are also more susceptible to the bacterial pneumonia can be a life threatening complication of flu.

These warnings aren’t just speculation. A number of scientific studies have shown that smokers have higher risk of influenza infection, as well as worse severity of infection. The studies showed that the infection rates were roughly 50% higher for smokers than non-smokers. Also smokers tended to have worse symptoms of cough, phlegm production, difficulty breathing, and wheezing. Loss of work occurred in 50% more smokers than non-smokers. (Arch Intern Med. 2004 Nov 8;164(20):2206-16. )

Some representative data from a study in the New England Journal of Medicine are shown below. [pending]