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article imageThe search for herd immunity with COVID-19

By Karen Graham     Feb 20, 2021 in Health
The U.S. is farther down the path to herd immunity on COVID-19 than Canada due to two factors: higher infection rates at the outset and, now, much higher vaccination rates. But, what is herd immunity?
The stories are similar, regardless of where they originated. For the past year, the coronavirus pandemic has clobbered communities across the United States, with some of the hardest-hit states - like North Dakota, South Dakota, and Arizona, seemingly close to being overwhelmed by the sheer numbers of cases.
CBC Canada relates the story of Winnipeg-born Doctor Rishi Seth, working in the COVID-19 ward at the Sanford medical center in Fargo, N.D. The doctor described the number of virus cases coming into the hospital as a "human tsunami, hitting a COVID-19 ward "which started on one floor, then expanded to another, and another."
"Call after call; hour after hour; every minute. Then our ERs were full. Then our walk-ins were full," he said, recalling one particularly bad shift in late 2020. However, things are different there now — and in many parts of the U.S. And it all comes down to the search for Herd Immunity.
Seth's hospital was treating 116 patients with COVID-19 at one point late last year. It now has eight. And it appears that in isolated pockets around the country, the same thing is happening as new cases fall dramatically. The change in infectivity is now offering a ray of hope - a light shining brightly at the end of a long, dark tunnel.
Nurses wearing personal protective equipment (PPE) attend to patients in a Covid-19 intensive care u...
Nurses wearing personal protective equipment (PPE) attend to patients in a Covid-19 intensive care unit at Martin Luther King Jr. Community Hospital on January 6, 2021 in the Willowbrook neighborhood of Los Angeles, California
Patrick T. FALLON, AFP
Falling cases - for various reasons
With close to 500,000 deaths, the American population has taken a direct hit on the chin from the deadly virus, yet the number of new cases and deaths are falling - down from their peaks in January.
About 59,800 Covid-19 patients were in US hospitals on Friday, according to CNN - down about 55 percent from a pandemic peak of more than 132,470 on January 6, according to The COVID Tracking Project. Overall, the number of coronavirus cases is down about 70 percent from the peak in Canada, and 75 percent in the U.S.
The U.S. has suffered three times more deaths than Canada per capita; its reported case count is four times higher; and, now, its vaccination rate is nearly five times higher.
All these factors, the number of new cases, deaths, and vaccination rates play a role in making the U.S. a step closer to mass-immunization and feeling more hopeful. This fact, in turn, brings us to the question: Is the U.S. getting closer to achieving herd immunity?
Aztec victims of the smallpox  Florentine Codex (compiled 1540–1585)
Aztec victims of the smallpox, Florentine Codex (compiled 1540–1585)
en:Bernardino de Sahagún (1499-1590), compiler. Original illustration by unknown 16th-century artis
What is herd immunity?
COVID-19 is a new disease, and people around the world have never before been exposed to the virus. So we had no immunity to fight it off, which puts us in the same place native Americans and other New World tribes were in when the Europeans and Spanish, with all their diseases, came to our shores.
Looking back in history, the people of the New World had never been exposed to smallpox, diphtheria, and other diseases that were taken for granted. Many people died from the new diseases until something called a threshold proportion was reached.
The Mayo Clinic explains it this way - "If the proportion of the population that is immune to the disease is greater than this threshold, the spread of the disease will decline. This is known as the herd immunity threshold.
You might ask, what proportion of a community needs to be immune in order to achieve herd immunity? That depends on how contagious the disease might be. More contagious diseases require more people to become immune in order to stop the spread.
Take measles, for example. It is extremely contagious and deadly, and that is why we have vaccines. It's estimated that 94 percent of the population must be immune to interrupt the chain of transmission.
Some ten percent of Americans have so far received at least one Covid vaccine dose  with Moderna acc...
Some ten percent of Americans have so far received at least one Covid vaccine dose, with Moderna accounting for just under half the number
JOEL SAGET, AFP/File
Achieving herd immunity
There are two ways to acquire herd immunity - vaccines and infection. Years ago, before we had a vaccine for chickenpox or varicella, people sometimes exposed themselves intentionally as a way of achieving immunity. And for less severe diseases, this approach might be reasonable.
COVID-19 is not the flu, or chickenpox. It is estimated that the coronavirus is over 10 times more virulent than the flu, so achieving herd immunity by purposely exposing yourself to someone who is sick with the virus is dangerous, due to the high risk of death.
Vaccines are the safest way to acquire herd immunity. They train our immune systems to create proteins that fight disease, known as ‘antibodies’, just as would happen when we are exposed to a disease. But here's the good part - vaccines work without making us sick.
To safely achieve herd immunity against COVID-19, a substantial proportion of a population - about 70 to 85 percent - would need to be vaccinated, lowering the overall amount of virus able to spread in the whole population. The U.S. does have a way to go to reach its goal of having herd immunity, but some experts think we are at least halfway there.
More about herd immunity, Covid19, Variants, vaccination rate, infection rate
 
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