Health & Fitness Why do we develop lifelong immunity to some diseases, but not others?

15:26  09 august  2020
15:26  09 august  2020 Source:   livescience.com

Herd immunity for Covid-19 ‘dangerous’ concept – WHO

  Herd immunity for Covid-19 ‘dangerous’ concept – WHO The global health body said ‘no-one is safe until everyone is safe’.Herd immunity is an epidemiological term usually reserved to describe how the population as a whole is protected from a disease depending on the levels of people vaccinated.

Some diseases , like the measles, infect us once and usually grant us immunity for life . For others , like the flu, we have to get vaccinated year after year. And where does the novel coronavirus fit into all this? Whether or not we develop immunity to a disease often depends on our antibodies, which

Our immune system is capable of developing antibodies to fight off bugs, as well as remembering them for the next time they attack the body. Herd immunity is achieved when a large enough proportion of the population is immune to an Others have switched off online appointment booking.

a woman sitting at a table: Childhood vaccines can protect against some diseases for a lifetime. © Provided by Live Science Childhood vaccines can protect against some diseases for a lifetime.

Some diseases, like the measles, infect us once and usually grant us immunity for life. For others, like the flu, we have to get vaccinated year after year.

So why do we develop lifelong immunity to some diseases but not others? And where does the novel coronavirus fit into all this?

Whether or not we develop immunity to a disease often depends on our antibodies, which are proteins we produce in response to infection. Antibodies are one of the body’s most well-known defenses: They coat invading cells and, in the best case, prevent those invaders from hijacking our cells and replicating. After we clear an infection, antibody levels often wane, but at least a few stick around, ready to ramp up production again if that same disease attacks again. That's why an antibody test can tell you if you were infected in the past. It's also what keeps us from getting sick a second time — usually.

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  Are You Immune To Coronavirus If You’ve Had It & Recovered? Since the start of the coronavirus pandemic, scientists and doctors have been working day and night to find ways to combat the global crisis. One of those solutions has been developing an antibody test to determine whether or not you’ve been exposed to COVID-19. But the question remains: If you have been exposed, does that mean you’re immune from catching it again? Knowing whether survivors are now immune is essential, because it will dictate how and when communities can start to resume their normal lives. If people who have recovered from coronavirus are now immune, they may be able to safely go back to work, for example.

For example, human-only diseases like Polio and Measles are nearly eradicated due to vaccination. The flu (Influenza) is easily transmitted and is in constant evolutionary battle with the human immune system, and every new flu season a new strain has evolved to evade our immune systems.

Yet, antibodies specific to some viruses can be lifelong . So, Jing Ning is asking why it is not true of A different flu vaccine has to be developed each year for the strains prevalent that year, and we get Why do some diseases confer immunity and others make you more vulnerable to recurrences in

Related: Can you get 2 colds at once?

"The body doesn't really forget," said Marc Jenkins, an immunologist at the University of Minnesota Medical School. Usually, when we get reinfected with a disease, it's not because our body has lost immunity. We get reinfected either because the pathogen mutated and our immune system no longer recognizes it, or because our bodies tend to mount a much lower immune response, he said.

Take the flu. This is a virus that can change its genes easily, Jenkins said. Just as our immune systems kill off one version of the virus, another emerges that our immune systems don't recognize. Not all viruses mutate so readily. For example, the polio virus can't easily change its genome, Jenkins said. That's why we've been so successful at (almost) eradicating it.

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In fact, some diseases are so rare now that parents sometimes ask if vaccines for them are even needed. The whooping cough (pertussis) vaccine also does not give lifelong immunity , and that may be one reason why outbreaks still happen.

In other words, we do develop long lasting immunity against the virus that causes us a cold today, but the virus that causes us a cold a few months later is somewhat different, and the Why RSV doesn't elicit lasting immunity --and in fact notably shorter immunity --is the subject of current research.

The common cold, and other viruses that don’t typically get past our upper respiratory tract, reinfect us not necessarily because they mutate rapidly, but because our body doesn't usually produce many antibodies against these pathogens in the first place, said Mark Slifka, an immunologist at the Oregon National Primate Research Center. "Our bodies are not worried about the upper respiratory tract," he said. That's what we're seeing with mild cases of COVID-19. The virus sticks to the upper respiratory tract, where the body does not treat it like a threat. In a 2020 preprint study (meaning it hasn't been peer reviewed yet) published in the database MedRxiv, 10 out of 175 patients who had mild symptoms recovered from COVID-19 without developing detectable antibodies.

For diseases that don't fall into either of these categories — meaning they don’t mutate rapidly and they generally prompt a strong immune response — immunity tends to last much longer. A 2007 study published in the New England Journal of Medicine found that it would take more than 200 years for even half of your antibodies to disappear after a measles or a mumps infection. The same study found similar results for Epstein-Barr virus, which causes mono. Still, antibody responses don't always last a lifetime. That same study found that it takes around 50 years to lose half of our chickenpox antibodies, and 11 years to lose half of our tetanus antibodies. That means that without a booster shot, you could theoretically become infected with one of these diseases as an adult.

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A. Diseases in which the immune system is not able to produce antibodies B. Diseases in which the immune cells' attacks do not affect the foreign agent C. Diseases in which the immune 9. (p. 278) Evidence suggests that some of the adverse effects of depression on immunity may be mediated by

For some diseases , herd immunity can go into effect when 40 percent of the people in a population The goal of herd immunity is to prevent others from catching or spreading an infectious disease To visualize this, picture someone without immunity as a red dot surrounded by yellow immune dots.

Scientists still aren't sure why we maintain our antibody responses longer for some diseases compared with others. It's possible that some of these more common diseases, such as chickenpox and mono, actually are reinfecting us more frequently than we realize, but that the antibodies we do have crush the infection before we notice, Jenkins said. And in those cases, the immune system would be at full capacity again and again because of the reinfections. "It keeps our immunity vigilant," he noted. In contrast, "with tetanus, we're probably very rarely getting exposed, we're not stepping on a [dirty] nail very often."

Related: Do rusty nails really give you tetanus?


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Other scientists point out that the human immune system is trained to target pathogens that "look" a certain way, Slifka said. Bacteria and viruses tend to be symmetrical with a repetitive pattern of proteins across their surfaces. (Think about COVID-19 — it's a ball with evenly spaced spikes all over it.) One theory suggests that we mount a larger and longer-lasting immune response to more repetitive-looking pathogens. For example, the antibodies we produce against variola, the highly repetitively-structured smallpox virus, last a lifetime. Tetanus, however, isn't repetitive at all. It's the toxin produced by tetanus bacteria, not the bacteria itself, that makes us sick. Based on this theory, it's possible that our bodies aren't as well-trained to target this single, asymmetrical protein, Slifka said.

So, will immunity to the new coronavirus — whether that comes from infection or a vaccine — be as long-lived as our immunity to smallpox, or will we need a new vaccine every year? While it’s true that some people aren’t mounting large antibody responses, Jenkins is still hopeful for the former. All the evidence both from natural infections and from vaccine trials suggest that most people are making neutralizing antibodies, the variety which prevents viruses from entering our cells, Jenkins said. And unlike the flu, SARS-CoV-2, the virus that causes COVID-19, isn't mutating quickly, Jenkins noted.

"This virus has the features of viruses that we've been very successful in vaccinating against," Jenkins said.

Originally published on Live Science.

Glimmers of hope for immunity in survivors of mild COVID-19 .
Recent studies suggest mild infections can result in sufficient immune responses to block the virus from invading a person's body again via not only antibodies but immune B and T cells.Much of the research and discussion of coronavirus immunity has focused on antibodies, with some suggesting these SARS-CoV-2-specific fighters provide little, weak, or only a brief shield from getting the virus again.

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