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Achieving natural herd immunity against COVID-19 cannot be safely or easily done

by Grailing Anthonisen - October 29, 2020   232 Views   9 min
Achieving natural herd immunity against COVID-19 cannot be safely or easily done


“Pox parties” are a good way to build immunity against COVID-19


Inaccurate (no factual basis; unacceptable margin of error)

A Daily Mail article from 23 October 2020 reported that Cambridge University Professor Paul Lehner claimed that deliberately infecting children to COVID-19 at “pox parties” could be a good way to help create herd immunity against COVID-19 without a vaccine. This claim is inaccurate because we do not know enough about immunity and herd immunity against COVID-19. In general, such parties are not recommended measures by public health authorities.

While natural infection is one of two ways to reach herd immunity in general, several factors are unknown about how to reach it for COVID-19 – and whether it is a good idea to reach it naturally. Achieving natural herd immunity when the mortality rate of a disease is as high as it is for COVID-19 could be considered unethical. It is unclear how many people would need to be infected or how long it would take for enough people to be infected. We also do not know how long people are immune to COVID-19 after recovering, which means that reinfection, though uncommon, is possible.

To support his claim, Lehner also suggested that children and young people do not get sick with COVID-19, which is false. Children can become severely ill and they can infect adults and other family members. Reaching herd immunity by allowing people to become infected naturally would drastically increase the mortality risk and leave many survivors with unknown health effects, some of which can be long-lasting.

What is a “pox party”?

Pox parties were a popular but controversial alternative to vaccination for diseases such as chickenpox – hence the term “pox party”. They involve bringing healthy non-immune children together and exposing them to a disease for which there is no vaccination, to create natural immunity against this disease for later in life. The US Centers for Disease Control warns against such a method of creating immunity.

What is herd immunity?

According to the Mayo Clinic, herd immunity is when enough people in a community, the herd, are immune to a disease, making that disease’s spread from person to person unlikely. The amount of people who need to be immune to reach herd immunity varies from disease to disease, depending on how contagious the disease is. There are two ways to reach herd immunity, vaccination and natural infection.

For COVID-19, it is still uncertain how many people would need to be infected and recover in order to achieve herd immunity. One study, a preprint, found that it was as low as 10-20% of the population, while another preprint found that herd immunity required 60-70% of the population to be immune. These numbers are based on theoretical calculations and models that may not hold true when put into practice.

There are, the Mayo Clinic notes, a number of drawbacks and uncertainties around reaching herd immunity through natural infection, including uncertainty as to whether COVID-19 infections make people immune and the risks of widespread infections overwhelming healthcare systems and creating preventable deaths. In a recent press conference, the Director-General of WHO, Dr Tedros Adhanom Ghebreyesus, called reaching herd immunity through natural infection, as health policy, “scientifically and ethically problematic”.

Does COVID-19 infection even make people immune?

It is uncertain how long the immunity to COVID-19 lasts after recovery. There is evidence that COVID-19 reinfection is possible. Journal of the American Medical Association has published a study of healthcare personnel who worked directly with COVID-19 patients. The study found that just two months after testing positive for COVID-19 antibodies, 58% of personnel didn’t have detectable COVID-19 antibodies anymore – their systems didn’t have enough immune properties (cells that create small weapons to attack the virus). The 42% of personnel who still had antibodies still experienced a sharp decline. Similarly, a pre-proof in the journal Immunity (a peer reviewed but not yet final version of a journal article) found that immunity from COVID-19 could last for up to 7 months.

The United States Centers for Disease Control and Prevention explains that the risk for reinfection may be lower than the first infection and it may be infrequent, but it is still possible. The possibility of being reinfected for many people is expected to increase as more time between recovery and the initial infection passes. Other coronaviruses can reinfect people.

How dangerous are infections for children?

Lehner reportedly said that young people do not get sick with COVID-19. This is not true. There are several dangers with purposefully infecting children. According to the US CDC, while most children with COVID-19 are more likely to have mild symptoms, they can still become severely ill and need hospitalization. Children with underlying conditions, like asthma or diabetes, are more at risk for a severe illness. According to Johns Hopkins Medicine, while 8 out of 100,000 children infected with COVID-19 require hospitalization— a lower level compared to 165 out of 100,000 adults—one third of these hospitalizations require intensive care.

Additionally, as we have previously explained on, COVID-19 is linked to an inflammatory disease in children. As Harvard Health notes, children are more likely to experience a complication known as multisystem inflammatory syndrome in children. This complication can lead to severe and life-threatening problems with the heart and other organs.

How dangerous is natural infection to other people?

There is a massive and unknown human cost to reaching herd immunity through natural infection. As explained in another of our articles, children can also transmit the virus to others, including family members who are more susceptible to severe infections. Children older than 10, according to the Canadian Medical Association Journal, are just as likely as adults to infect others. Due to a gap in research, it is uncertain as to whether this is true for children younger than 10 years old. According to Harvard Health, children infected with COVID-19 had as much, or more, coronavirus in their upper respiratory tracts as infected adults. This means that even if they are asymptomatic or have very mild symptoms, they can still infect others.

Internationally, according to the World Health Organization (WHO), there have been more than 1.1 million COVID-19 deaths as of 27 October 2020. In Canada, according to Canada Public Health, 9,922 cases of 213,959 cases have been fatal. People who are 60 years or older and those with underlying conditions are the most susceptible to severe forms of COVID-19 or death.

Not everyone is equally affected by COVID-19. Racial and ethnic minority communities are much more likely to suffer serious cases and die from a COVID-19 infection. This is mainly due to underlying issues associated with minority communities such as living in crowded housing conditions, working in essential fields, a greater likelihood of having underlying conditions, inconsistent access to healthcare, to name a few. According to Johns Hopkins Medicine, this is the case for people of color generally, and Black Americans specifically, in the United States. This holds true for children and youths 21 years and younger. The US CDC found similar results. A survey found that Hispanic Americans, Black Americans and Indigenous Americans are disproportionately affected by COVID-19 and more at risk for severe infections and death. According to the Lancet, this is the case for the United Kingdom as well. Similarly, the Canadian research group INNOVATION, in partnership with the African-Canadian Civic Engagement Council, found that Black Canadians are much more likely to report symptoms, seek treatment, and nearly three times as likely to report knowing someone who has died of the virus.

According to WHO, 10 to 15% of all cases of COVID-19 become severe. Some cases result in a prolonged illness, leaving people feeling that they do not fully recover. People, including young adults and people with no underlying medical conditions who were not hospitalized, can still experience prolonged and persistent symptoms. Indeed, even when people survive infection, COVID-19 may lead to or increase the risk for long-term health effects, such as heart damage and heart failure, lung damage and cognitive impairment, affecting memory and concentration.

The Sweden experiment

Sweden has been one of the louder proponents of the herd immunity strategy and while it has implemented public health measures since the start of the pandemic, these measures have been less severe than in many other countries. Their Public Health Agency and Prime Minister haver referred to herd immunity as “common sense” health policy to counter the COVID-19 pandemic. This strategy has been shown to be less effective and to have a real human cost. According to Johns Hopkins Medicine, Sweden has the 17th highest per capita death rate in the world for COVID-19, and a case fatality rate of 5.4%. A study published by the Journal of the American Medical Association shows that Sweden has a high overall rate of death that has not gone down since the pandemic began. Cases and outbreaks in Sweden continue to rise and it is uncertain when or if Sweden will reach herd immunity through the strategy of implementing more relaxed public health measures.

Proposing strategies when we don’t know enough about a disease can cost lives

The claim that pox parties are a good way to build immunity against COVID-19 is inaccurate. It is uncertain how many people would need to get infected. It is also uncertain how long people remain immune after a COVID-19 infection, and reinfection is possible. Children can still experience severe cases and, if they are 10 years and older, are just as capable of spreading COVID-19, causing severe and deadly cases, and disproportionately affecting minority communities. Using natural infection to reach herd immunity puts an unknown number of people at risk, not just for death, but for lifelong health effects, like heart, lung, and brain damage.

Lehner’s statement is not just inaccurate, it is erroneous. It is also by no means unanimous in or reflective of the rest of the scientific community. Indeed, thirty-one other experts recently authored an article, published in the Lancet, referring to herd immunity from natural infections as “a dangerous fallacy unsupported by scientific evidence.” In circumstances such as these, it is a good idea to consider health and policy advice not just from one individual, but from the wider community and larger bodies, such as the US CDC, Canada Public Health and WHO.

Aside from natural infection, vaccines offer the only other pathway to herd immunity. As discussed in a previous article published on, it is uncertain when a vaccine against COVID-19 will be ready and how long immunity will last from it. However, there are still a few strategies to reduce COVID-19 infections while waiting for mass production and distribution of a vaccine. They include physical distancing, contact tracing and testing, and wearing masks.

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Canada Public Health:

Canadian Medical Association Journal:

Harvard Health:



INNOVATION Research Group:


Johns Hopkins Medicine:

The Lancet:


The Mayo Clinic:


Population Health

World Health Organization:

Swedish COVID-19 strategy


Daily Mail

“Pox parties” are a good way to build immunity against COVID-19


Inaccurate (no factual basis; unacceptable margin of error)

 October 29, 2020


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