A Dangerous Route in Fighting Coronavirus: Herd Immunity – Population Immunity
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Although most countries worldwide use similar methods to suppress the coronavirus pandemic, some countries are trying to manage the pandemic through herd immunity (population immunity).
The aim of the approach called "herd immunity" in English is to allow large numbers of people to contract the disease, thereby enabling society to develop immunity to the disease. Although the virus would spread through the community in a short time, it is thought that transmission would naturally stop because most of the population would also have gained immunity.
The United Kingdom previously announced that it would use the herd immunity approach, and this was its initial response to the outbreak. However, it abandoned the approach after realizing that more than 250 thousand people would die in the United Kingdom alone. This time, however, the Netherlands reported that it planned to use herd immunity to combat the coronavirus outbreak, just as the United Kingdom had initially planned.
Regarding herd immunity, the World Health Organization (WHO) emphasized the need to plan more extensive action against the virus, while some health experts described herd immunity as "the best approach experimentally, but the most dangerous in terms of its consequences".
Can Herd Immunity Protect Us from the Coronavirus?
How Does Our Immune System Work?
Our immune system fights infectious diseases such as coronavirus. The immune system's B lymphocytes produce antibodies to fight and destroy invading organisms. These antibodies also act as a “memory” of the microbe, enabling a better and faster response on encountering it again. In other words, once a person develops immunity to a virus, they are thought unlikely to contract it again.
This is actually the theory behind herd immunity. According to this theory, if the favorable scenario occurs, “when many people develop immunity to a virus, eventually they will not transmit the disease to people who have not yet contracted it. Transmission will thus end.”
The Importance of Numbers in Herd Immunity!
Herd immunity is essentially a numbers game. All plans are based on one person transmitting the infection to another. However, the transmission rate is crucial to the entire plan. A rate of “1” means one person will infect at least 1 other person. A rate >1 (more than one) means the infection will spread rapidly. Herd immunity aims to bring the reproduction rate below <1, the point at which infection stops spreading.
The estimated transmission rate for coronavirus is between 2-3
Accordingly, for measles transmission to end, 95% of people need to be immune. With a transmission rate calculated as 2.6, herd immunity in 60% of people would be sufficient to stop coronavirus transmission. Recently, however, data have begun arriving from China indicating that some recovered individuals can become infected a second time. Experts explain this as follows: “Recovered patients may not produce enough antibodies to develop immunity to SARS-CoV-2 and may become infected again. The virus may also be "biphasic," meaning it may remain dormant before producing new symptoms”. Another striking finding emerged from investigations on the cruise ship Dimond Princess, carrying 700 COVID-19 patients from China to Japan: He and Kenki Mizumoto of Kyoto University published a report showing that, on the day quarantine began aboard the ship, one person could spread the virus to at least 7 people. However, some views suggest this does not reflect the normal world. The novel coronavirus's transmission rate, called R0, is currently accepted to be between 2.5 - 3, approximately 4 times faster than influenza (seasonal flu).
Is Herd Immunity a Wise Plan?
On 31 March, US President Trump gave a lengthy speech about the COVID-19 outbreak with his White House team. He announced that the estimated number of COVID-19 deaths in his country would be 100 - 240 thousand "if the measures are strictly enforced." In the worst-case scenario, if Americans live without taking precautions—that is, if herd immunity is applied—the estimated death toll would exceed 2 million...
The best way to develop immunity to viruses quickly and safely is vaccination. Vaccination introduces a small amount of a virus or virus fragments into the body, and the immune system learns how to fight without having to become ill. However, a vaccine developed for the coronavirus is not yet available.
In an infection spreading without a vaccine, even if some people are not severely affected by the disease (approximately 80%), they can transmit the virus to older people at high risk of death. A report by some experts stated that more than 47 million people in the United Kingdom would need to become infected for herd immunity to develop. With a mortality rate of 2.3% and a severe-disease rate of 19%, this could cause more than one million deaths and leave eight million people needing critical care.
What Should Be Done?
Suppose Australia and New Zealand rely on herd immunity. Assuming no external influences and that the infection exists only in this region, let us suppose 10% of the population is infected. This corresponds to 500 thousand New Zealanders and 2.5 million Australians. That would be enough to overwhelm and collapse these countries' healthcare systems in a short time.
The safest public health strategy is protection from the virus through social and personal isolation and hygiene rules.
Preventing or delaying the onset of coronavirus infection is critical. Preventing its spread is important at the second stage. These strategies buy time for the healthcare system and “flatten the curve” of the outbreak's growth, so hospitals do not have to be overwhelmed by cases all at once.
It is therefore very important to isolate as much as possible, control movement within our living boundaries, restrict and avoid public gatherings, trace the contacts of infected people and identify those with the disease. Both Australia and New Zealand are essentially following these measures.
It is also important to educate the public about safe hygiene, ensure supplies of hand sanitizer, safe food, soap and water, and provide access to disinfection services when needed. Taking extra care of older people, especially by being cautious about contact, is also very important during this period.
If everyone heeds the warnings and follows precautions carefully, the consequences of the coronavirus outbreak will be milder. We firmly believe that afterward our world will become an even better place than before.
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Sources
2. Trump warns of 'painful' two weeks ahead as White House projects more than 100,000 coronavirus deaths. https://edition.cnn.com/ 31 March 2020
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