What we have learned so far about infectious diseases such as COVID-19 is that they move and spread chaotically, jumping from host to host within people, without borders. And this is exactly what is happening all around the world with Corona Virus disease in 2020.  There are many things we still don’t know about it, but what we learned from experience is how the virus spreads: “COVID-19 is primarily transmitted from symptomatic (or asymptomatic) people to others who are in close contact. This can happen through respiratory droplets, by direct contact with infected persons, or by contact with contaminated objects and surfaces.” (1)

But, what if we become immune to the virus after we get it?

This is the question scientists, but also regular people, all over the world are trying to answer. Everyone have been wondering what would happen if the entire population got exposed to the virus. Would it bring up a new solution for society?

Changing the number of immune people could absolutely influence society, and it’s easy to understand why. When many people are immune, each infection has fewer opportunities to spread to a new individual.  “When most of a population is immune to an infectious disease, this provides indirect protection – also called herd immunity – to those who are not immune to the disease.“ (2)

Herd immunity is the idea that if enough people are vaccinated and immune in society (70-80% of the population) the virus won’t be able to spread so easily. The percentage of people needed to be immune to develop herd immunity depends on the transmission rate of the disease. “R0, pronounced R naught, is a mathematical term that indicates how contagious and infectious disease is. […] R0 tells you the average number of people who will contract a contagious disease from one person with that disease. It specifically applies to a population of people who were previously free of infection and haven’t been vaccinated.” (3)

The more transmissible is the virus, the more people need to become immune. There are two possible ways to achieve herd immunity: one is thought vaccination (the keyword here is time) while the other, more dangerous, is an intentional exposure to the virus by the whole population.


In a nutshell, when more people are immunized, fewer and fewer people are likely to get an infectious disease. In such scenarios, it is way easier to control the spread of the virus. On the contrary, when no one in the community is immunized, the chances of an infectious disease spreading are extremely high. The more people get immune, the less the community is going to face high numbers of infected people.

As we suggested before, a sufficient amount of immune people can actually cease the spread of the virus. This provides immunity to the entire population/community. And this is herd immunity.


To give you an easier example:

In the past, many parents used to take their children to the so-called “chickenpox parties” to bring them into contact with other children who had the disease.

“In the days before there was a vaccine for chickenpox, parents used to hold “pox parties,” intentionally exposing their children to chickenpox in an attempt to build up the child’s immunity to the disease. That sort of worked—though the Centers for Disease Control and Prevention strongly recommends against hosting such parties, given the risk. And chickenpox is far less deadly than COVID-19 appears to be.” (4)

If we want to analyze the actual scene in which the herd immunity could be applied there is an enormous problem that could not be solved using this approach. Let’s see what it is about.

“Other viruses (like the flu) mutate over time, so antibodies from a previous infection provide protection for only a short period of time. For the flu, this is less than a year. If SARS-CoV-2, the virus that causes COVID-19, is like other corona-viruses that currently infect humans, we can expect that people who get infected will be immune for months to years, but probably not their entire lives.”(5)

So it is also a matter of understanding for how long a person will be immune.


The possibility of herd immunity cannot be reflected in reality, it does not apply to a virus like this and could have fatal consequences. Scientists don’t know yet for certain if the human body even develops immunity to COVID-19, and even if it does develop immunity, we don’t know how long it will last.

“Based on previous research into other coronaviruses (such as those that cause MERS and SARS), experts do believe it is likely that someone infected with COVID-19 will have some level of immunity after recovering from the illness, but the details are still very much unknown. Which is why, they say, it’s a terrible idea to purposefully expose yourself to infection. […]

“David Dowdy, associate professor of epidemiology at Johns Hopkins University, says researchers think only about 1 to 2% of the U.S. population is currently immune to the virus. “It may be higher in places like New York City, but to get to 1 to 2% [immunity], we’ve already had over 40,000 deaths,” he says. “To get to 70% of the population being immune through natural protection, you’re talking hundreds of thousands of deaths, so not a good idea.”[…]

“I also feel like people are confusing the idea of individual immunity and herd immunity,” Dowdy adds. “If people are thinking of intentionally exposing themselves, they shouldn’t be thinking in terms of herd immunity, they should be thinking in terms of the risk-benefit to themselves…that’s a big risk to take and not one that I think is a wise choice.” (6)

Therefore, the real problem is that the application of the concept of herd immunity in the society would mean to sacrifice more vulnerable people (usually older or immune-depressive people) for the good of the more healthy ones. We have to think that when exposing ourselves to the virus we are also exposing our friends, family and coworkers and we don’t know how their bodies will react to the exposure.

Over the past months we have seen a few examples of states who experienced (or tried to experience) the application of such theories.


Many newspapers have been reporting the possibility of “Covid-19 parties” in the US, just like the so-called “chickenpox parties” happening in the past. Some of the young in fact think that by joining these parties and getting infected, they will be immune sooner than the people who are self-isolating, and therefore they will be ready to go back to work sooner than the others. In these parties, the guests mix with sick people, positive to the virus, in order to be infected and to be able to develop antibodies.

The idea of ​​”Covid-19 parties” appeared especially after health authorities around the world began to consider the idea of ​​immunity passports, a document that would certify the absence of risk of contagion of the person who owns it. Therefore, that will allow those who have tested positive for the virus and then recovered to travel or return to work faster.

The Centers for Disease Control and Prevention (Cdc), the federal body that deals with public health in the United States, advise against Covid-19 parties, emphasizing that young people who are exposed to contagion in most cases do not need hospitalization to heal, but the risk is that more vulnerable people, such as older or immune-depressive people, will become infected if young infected people don’t take social distancing seriously.


Another example could be reported by the UK. At the beginning of March, when the virus started to spread all around Europe and Italy had just entered in lock down, the prime minister of United Kingdom, Boris Johnson, announced the country’s strategy against the virus: schools were going be open, no calls to stay at home, postponing radical measures and only proposing practices such as the invitation to wash hands often. It really seemed that his plan was to develop herd immunity. In fact, on March 13th the executive’s scientific adviser, Professor Patrick Vallance, evokes in an interview the hypothesis of an alternative strategy to lock down in order to hope to arrive at a form of “collective immunity” (herd immunity). The government in the days immediately following denies that this is its plan, but the controversy grows.

On March 16, a statistical study by Imperial College London and Professor Neil Fergusson predicted at least 250,000 potential victims in the UK due to the absence of lock-downs, convincing the prime minister to stop any “non-essential” social contact and work.

March 20.  Compulsory closure of schools, pubs, restaurants, gyms, and cinemas.

March 23. General lock-down

March 27. Boris Johnson tests positive for the virus

“What explains the sudden change of course? The established narrative suggests that the government’s strategy for managing the pandemic initially depended on herd immunity. But the combination of public revulsion at the government’s apparent readiness to let tens of thousands get sick and die, combined with a frightening report published by Imperial College London (with a death toll of up to 250,000), forced the government to embrace new containment strategies.” (7)


While the rest of Europe has adopted drastic measure for the economy such as lock down and isolation, Sweden has chosen to take the path of the first statements by Boris Johnson and Trump: “light” containment measures that allow not to destroy the health system, also preventing socioeconomic impact in the entire country over the medium to long term.

Sweden’s strategy has to do with more relaxed measures and few restrictions to control the spread of corona virus, to try to live with the virus and achieve herd immunity without trauma. Despite some restrictions, such as a ban on public gatherings of more than 50 people and an obligation to separate restaurant tables, the streets remain crowded, bars are still open and elementary schools aren’t closed. Instead of imposing widespread restrictions, the Swedish government has advised its citizens to act responsibly, practicing social distancing and staying home when sick. The over-70s were asked to self-isolate.

Sweden is a country of about 10 million people, and as “24 May 2020, there have been 33,188 confirmed cases of COVID-19 with 3,992 deaths”. (8) The majority of the population continues to support their government’s approach. Many argue that Swedes practice social distancing as a cultural habit, others consider this as an example of the mutual trust between the state and the people that makes Sweden unique.

However, “only 7.3% of people in Stockholm had developed the antibodies needed to fight the disease by late April”, “Sweden’s percentage of people with antibodies is not far off that of other countries that did enforce lock-downs. In Spain, 5% of people had developed corona virus antibodies by May 14, according to preliminary results of an epidemiological study by the government.” (9)

The chief epidemiologist Tegnell told BBC radio that the adopted strategy put Sweden in a better position to deal with a second wave of Covid-19 cases with 15-20% of the population now immunized, not enough for herd immunity but enough to slow down and control the spread of the infection. He said the strategy had “worked in some aspects … because our health system has been able to cope. There has always been at least 20% of the intensive care beds empty and able to take care of Covid-19 patients.” (10)

Moreover, many people have decided to stay at home anyway, the mobility is only slightly higher in fact compared to other Scandinavian countries the markets are also not going so well. “Sweden’s central bank said in a recent report that it forecast an economic contraction for Sweden of between 7 and 10 percentage points for this year and unemployment of between 9 and 10 percent. Last year the jobless figure was 6.8 percent. The European Commission’s current forecast for the euro zone for 2020 is for an economic contraction of 7.75 percent.” (11)


After all, even though we have the actual scientific proof that herd immunity has been realized before, we still don’t have any example of a country dealing well with it in this exact situation. Nevertheless, we also need to consider the high probability of the virus changing and transforming by himself, as happened before. Then, this can be considered as a strategy only in the eventuality that it proves his effectiveness, with a retrospective view. The concept of Herd Immunity could only work well for an agent that infects little, with low mortality and if it applies to diseases of which we already have a vaccine, things that do not apply in the present case. And as it is being shown, this virus requires very high immunity rates. Furthermore, when applied, Herd Immunity will not keep safe at all a considerable slice of the society, such as immune depressed and elderly people with progressed pathologies, provoking the death of weaker people, and not fulfilling what should be one of the main objective of a State: to protect and help its people, especially the fragile ones.

So, what to do in the meantime?

The risks must be reduced, behavior must be changed in the long run by wearing masks, washing hands, keeping physical distances, changing our lifestyle, while waiting for the vaccine or for the virus to naturally disappear.

Written by: Benedetta Stabile & Marisa Castelli

Sources & Citations:

  1. www.who.int › docs › situation-reports › 20200402-sitrep-73-covid-19
  2. https://www.jhsph.edu/covid-19/articles/achieving-herd-immunity-with-covid19.html
  3. https://www.healthline.com/health/r-nought-reproduction-number
  4. https://time.com/5825386/herd-immunity-coronavirus-covid-19/
  5. https://www.jhsph.edu/covid-19/articles/achieving-herd-immunity-with-covid19.html
  6. https://time.com/5825386/herd-immunity-coronavirus-covid-19/
  7. https://www.newstatesman.com/politics/uk/2020/04/real-reason-uk-government-pursued-herd-immunity-and-why-it-was-abandoned
  8.  https://covid19.who.int/region/euro/country/se
  9. https://edition.cnn.com/2020/05/21/health/sweden-herd-immunity-coronavirus-intl/index.html
  10. https://edition.cnn.com/2020/05/21/health/sweden-herd-immunity-coronavirus-intl/index.html
  11. https://www.politico.eu/article/swedens-cant-escape-economic-hit-with-covid-19-light-touch/

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