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Vaccines are on everyone's mind lately - since they offer hope that COVID-19 can be contained, even defeated. But we're hearing that most folks don't understand how they work or what can be expected from them. So here's our 101 on the immune system and vaccination.


How the immune system works


The body's multilayered defense against infection works like this: Bacteria and viruses can be stopped by the quick response of your innate immune system when the microbes come into contact with your skin or your nasal and intestinal layers. Inflammatory cells and soluble proteins get activated. Blood circulation increases and an affected area can become swollen and hot. Sometimes you get a fever.


If that doesn't eliminate the invader, then scavenger cells or phagocytes get into the act in the body's tissue and blood, gobbling up the pathogens. Hungry macrophages (a kind of white blood cell) react to the antigens (parts of the invading germs). Natural killer cells then get into the act, identifying cells in your body that are infected, so that those killer cells, along with white blood cells that produce antibodies, can be activated. This is as your adaptive immune system.


You need that second line of defense because often your innate immune system cannot mount a response that stops a virus from getting into your body and multiplying. The adaptive immune system launches a more targeted reaction using the immune system's T and B cells, which can spot specific invaders in tissue and fluids, but it can take several days (or more) for there to be a robust response.


Bonus: Those T and B cells often have a memory of their encounter with an invader. This memory can remain in the body, sometimes for years, waiting to defeat any subsequent infection by the same pathogen. Some infections, say mumps or measles, you can only get once in your life since these cells' memory summons a response that can vanquish the virus whenever it appears.


How vaccines work with your immune system


Vaccines are designed to stimulate your body's built-in defenses to infection without exposing you to that full-blown disease. They do this by introducing an altered version of the infecting agent -- one that makes your immune system mistakenly think you are being attacked by a fully active virus when you are not. This revs up your killer T cells and your antibody-producing B cells, stopping a virus before it makes you sick. The vaccines to COVID-19 (there are scores in development) work on these principles - some using very innovative ways of triggering your defenses to produce neutralizing antibodies.


Which of the COVID-19 vaccines will be most effective for which groups of people remains to be seen, but what we do know is that overall, vaccines are one of the most incredible developments in modern medicine -- transforming the life of billions of people who would otherwise be killed or seriously harmed by infection with everything from smallpox to HPV. A new study published in the Annals of Internal Medicine has found that over a 20-year period 57 vaccines have been used with very few complications - although in post-marketing reviews there have been revisions to who might receive them because of age, allergies or co-conditions, and one vaccine was withdrawn from market altogether. The authors urge people to remember that because of vaccines "the incidence of once common infections, such as measles, mumps, pertussis, rubella and poliomyelitis, has decreased by more than 90 percent, and some diseases have been all but eliminated."


So, watch for the launch of various COVID-19 vaccines and feel confident they'll up your chance of dodging the infection. Experts estimate we need 55 percent to 82 percent of folks getting the vaccine for widespread protection. We will write about the vaccine when we judge it's safe enough to get ourselves - and we hope you'll get yours then, too. It'll be worth a shot!


Mehmet Oz, M.D. is host of "The Dr. Oz Show," and Mike Roizen, M.D. is Chief Wellness Officer and Chair of Wellness Institute at Cleveland Clinic. To live your healthiest, tune into "The Dr. Oz Show" or visit www.sharecare.com.


Distributed by King Features Syndicate, Inc.