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Herd immunity is over – long live superimmunity

Forget about herd immunity. Covid-19 vaccines and previous infections do not provide lasting protection against infection and transmission, especially with the Omicron variant. This makes it impossible for enough of the population to become immune to stop the virus from spreading.

But do not despair. Omicron will provide a large portion of the population with what some scientists call "superimmunity" - stronger protection against new variants and even future coronavirus. Normal life will be possible even if the virus continues to spread and mutate. Superimmunity will not necessarily prevent people from becoming infected or transmitting the virus. However, most people who become infected, even with a more virulent variant, will experience mild or no symptoms.

To understand why, consider how the immune system works. Two types of white blood cells, T and B cells, tag team to overcome invading pathogens. T cells act as sentinels circulating in the lymph nodes and bloodstream. When they spot an attacker, they get started. A type of T cell destroys infected cells. Another signals B cells, the power multipliers of the immune system, to proliferate and secrete antibodies that neutralize the pathogen. Antibodies target proteins on the pathogen known as antigens.

Once the army of white blood cells and their antibody-foot soldiers have defeated the virus, most die. But some white blood cells that remember the pathogen continue and improve their fighting skills. These so-called memory T cells continue to reside in the bone marrow, lymph nodes and other tissues, ready to mobilize the immune system if they encounter the uninvited guest again.

Meanwhile, memory B cells go to boot camp in the lymph nodes, where they come into better combat shape if the attacker returns. Memory B cells train to produce antibodies that can block new variants. When and if the virus reappears, they can reproduce faster and produce more potent antibodies.

Vaccines mimic natural infection by training the immune system with a pseudovirus or antigen - in the case of Covid-19, the tip of the surface of the virus that it uses to bind to human cells. Antibodies produced after vaccination tend to decrease faster than after infection, perhaps because the virus particles last longer in the body than the vaccine-simulated antigens.

With both infection and vaccination, the immune system becomes faster, stronger and smarter after being exposed to a new challenge. Researchers have found that people who have been infected with Covid-19 and later vaccinated show higher levels and a wider range of antibodies that last longer than people who have only been vaccinated.

Similarly, a study from Oregon Health and Science University last month found that vaccinated people who experienced breakthrough infections produced higher levels of antibodies that were up to 1,000% more effective than those generated two weeks after a second dose of Pfizer. vaccine. The researchers described this as superimmunity.

"I think this speaks to a final playoff," said co-author Marcel Curlin. "That does not mean we are at the end of the pandemic, but it does indicate where we are likely to land: Once vaccinated and then exposed to the virus, you will probably do reasonably well - protected from future variants." Dr. Curlin added: "Our study suggests that the long-term outcome will be a phasing out of the severity of the worldwide epidemic."

A study from South Africa last month showed that people infected with Omicron produced antibodies that were more than four times better at neutralizing the Delta variant. Booster vaccines also enhance the immune response by giving B cells more time to mature - one of the reasons why antibodies after three Pfizer shots are able to neutralize Omicron in laboratory experiments, while after two they are not.

But boosters train the immune system towards the same goal. Omicron's innumerable mutations create a greater challenge for the B and T cells, thereby strengthening the immune system. To use an analogy, if you practice doing push-ups, you will become stronger - but not as strong as if you also did pull-ups.

Infection also strengthens the T cell response. T cells from vaccinated humans have been shown to retain 70% to 80% of their efficiency against the Omicron variant spike protein. This has helped prevent more serious illness, although vaccine antibodies are less effective against Omicron.

But infection trains T cells to recognize viral proteins that are also less likely to mutate than the tip. Some of these proteins share similarities to the original SARS virus as well as four coronaviruses that can cause colds. SARS survivors have been shown to have memory T cells 17 years after infection, which also recognized parts of the Covid-19 virus. A new study from the British Imperial College showed that people with pre-existing T cells for non-spike proteins in common cold viruses were less likely to become infected with Covid-19.

All of this suggests that infection with Omicron is likely to stimulate potent and lasting protection against Covid-19 - and potentially other coronaviruses - even if it mutates to become more virulent. As Omicron spreads rapidly, individuals who have been vaccinated or previously infected will develop superimmunity. Covid-19 will be a virus that causes cold and sometimes flu-like symptoms - annoying, but rarely fatal or disruptive.

One caveat is that older people generate weaker T cell responses and are reminiscent of infections and vaccines. They probably need annual booster shots. Omicron will end the pandemic by making Covid-19 endemic.

Ms. Finley is a member of the magazine's editorial board.

The journal's editorial report: Paul Gigot interviews Dr. Marty Makary. Photos: AP / AFP / Getty Images Composition: Mark Kelly

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