Position Statement No. 4: COVID-19 Advisory Team Position Statement on the dangers of trusting in herd immunity

We are all exhausted by our continual battle against the COVID-19 pandemic, on both the individual and social level, therefore the prospect of achieving herd immunity seems like an attractive goal. However, experts agree that in the long term, the only way of bringing the pandemic under control is to develop an effective vaccine or treatment for severe symptoms of COVID-19.

Herd immunity can be achieved by vaccinating a sufficiently large proportion of the population, and according to the most optimistic scenarios this could happen as early as 2021. The threshold for herd immunity is currently estimated based on theoretical calculations. Most mathematical models indicate that between 50 and 70% of the population will have to be immune before the pandemic can be said to be under control (1). This number could be lower – 10-20% (2) – if the infection were mainly spread by unusually contagious individuals known as super-spreaders. However, according to the latest data, the role played by super-spreaders seems to have been overestimated. Many studies into the structure of interpersonal relationships show that there are simply not sufficiently high numbers of people with such extensive networks of contacts in the population (3). Additionally, although in certain regions, e.g. Lombardy (4) and Madrid (5), around 15-20% of the population had been infected with SARS-CoV-2 in spring 2020, current infection levels in those regions do not indicate herd immunity. This means that either the percentage of the population who have developed immunity needs to be higher to achieve herd immunity, or individuals who had already been ill with COVID-9 have lost their immunity.

So should we simply allow the virus to spread freely and then, once herd immunity reaches around 60%, go back to normal? The answer lies in numbers. If we were to follow this scenario, over 22 million people in Poland would become infected over the course of a few months. According to data on the clinical course of COVID-19 (6), between 0.4 and 4.7% of patients aged under 40 require hospitalization for at least ten days and the number increases to between 6.1 and 36.4% in patients aged 80 and above. Deaths of COVID-19 are rare in patients aged 40 and below, rising to 2.1% in patients aged between 60 and 80 and 8% in those aged over 80. If the virus is allowed to spread freely among older people, many will not survive, hence the idea that people aged 60 and above should isolate so to allow the population to reach herd immunity without major health consequences.

However, even if only younger people were getting infected, the number of patients would still likely exceed a million in the coming months. This vastly exceeds the capacity of the healthcare system, which in turn constitutes a major threat to other patients. It would mean people with chronic illnesses or those requiring emergency treatment would be denied medical care. Such cases are also victims of the pandemic, even though they are not included in the statistics. Therefore, according to research conducted in the UK, if the strategy of achieving herd immunity were to have any chance of succeeding, the spread of the virus must be halted among younger people by enforcing social distancing, mask wearing and potentially closing schools and workplaces (7). According to estimates, this would mean periodically tightening then loosening restrictions over a period of between seven and 12 months, with older people remaining in isolation throughout and not seeing their children and grandchildren.

What would this mean? It would mean no access to hospitals and medical care and a lack of daily help and support. It would entail complete isolation at home for people who are frequently excluded from the digital world. It would mean high numbers of preventable deaths due to chronic conditions or simply due to no access to healthcare and medication. Empirical experience of countries such as Sweden and the UK shows that isolating large social groups is simply impossible.

Let us briefly assume that we made such a decision, to bear these terrible costs in our struggle against the pandemic. Unfortunately any victory would be entirely pyrrhic. How long natural immunity to SARS-CoV-2 persists remains unclear, but we do know that antibody levels drop with time. We also know that for other coronaviruses, immunity is maintained for between a few months to two years, therefore it is not out of the question that some people who were ill with COVID-19 back in the spring could already be infected again. Reports of reinfection, so far sporadic, may confirm this. Although it is likely that subsequent infections would result in milder symptoms, individuals who have been ill with COVID-19 continue to spread the infection, meaning that all the sacrifices and victims would have been in vain. This would result in recurrent epidemics, as was the case with numerous infectious diseases before the advent of vaccination. We also do not know the long-term effects of COVID-19. Recent reports indicate that many patients, including young people, experience long COVID-19 and post-COVID syndrome which can severely affect their social and professional lives and leave an indelible mark on society as a whole (8).

The stance adopted by international scientific circles leaves no room for interpretation. Currently, pursuing strategies of natural immunity is described as a “dangerous fallacy unsupported by scientific evidence”(9).

Why do we believe that a vaccine will be more effective? Vaccination can be followed by booster doses with no risk to the patient, in order to train our immune systems to remember the SARS-CoV-2 virus for longer. We would therefore like to stress that any ongoing discussions should abandon the idea of natural herd immunity and focus on future measures, such as developing a vaccine against COVID-19 and defining the priorities and logistics for mass vaccination programs taking into account the complex international demographic situation.

In the meantime, we must continue to strictly adhere to social distancing (at least 1.5m), wear a mask covering the nose and the mouth, maintain high levels of hygiene (washing our hands regularly with soap and hot water) and avoid crowds and spending time with other people in enclosed surroundings.

About the Team

Professor Jerzy Duszyński, President of the Polish Academy of Sciences (PAS), will chair the Team. Prof. Krzysztof Pyrć, a specialist in microbiology and virology from the Jagiellonian University in Cracow, will be his deputy, while Dr. Aneta Afelt, a health geographer from the Interdisciplinary Center for Mathematical and Computational Modeling at the Warsaw University will be the Team’s secretary.

Members of the COCID-19 Advisory Team:

  • Prof. Radosław Owczuk (Medical University of Gdańsk),
  • Anna Ochab-Marcinek, PhD, DSc (PAS Institute of Physical Chemistry),
  • Magdalena Rosińska, MD, PhD, DSc (National Institute of Public Health – National Institute of Hygiene),
  • Prof. Andrzej Rychard (PAS Institute of Philosophy and Sociology),
  • Tomasz Smiatacz, MD, PhD, DSc (Medical University of Gdańsk).

The Chair of the Team may invite other individuals to take part in the work of the Team, with an advisory vote.

Scientists will actively monitor the epidemic situation in Poland. They will determine all the possible scenarios and make appropriate recommendations. They will also establish cooperation with similar groups in other countries to exchange knowledge and benefit from their different experiences on this matter.

The interdisciplinary COVID-19 Advisory Team was established at the Polish Academy of Sciences on June 30, 2020. The team will finalize its work on December 31, 2021. Members of the Advisory Team do not receive remuneration for their services.


  1. Omer SB, Yildirim I, Forman HP. Herd Immunity and Implications for SARS-CoV-2 Control. JAMA. Published online October 19, 2020. doi:10.1001/jama.2020.20892
  2. Gomes MGM, Corder RM, King JG, et al. Individual variation in susceptibility or exposure to SARS-CoV-2 lowers the herd immunity threshold. Preprint. medRxiv. 2020;2020.04.27.20081893. Published 2020 May 2. doi:10.1101/2020.04.27.20081893
  3. Prem K et al. Projecting contact matrices in 177 geographical regions: an update and comparison with empirical data for the COVID-19 era. medRxiv 2020.07.22.20159772; doi: https://doi.org/10.1101/2020.07.22.20159772
  4. Pagani G et al. Seroprevalence of SARS-CoV-2 significantly varies with age: results from a mass population screening. medRxiv 2020.06.24.20138875; doi: https://doi.org/10.1101/2020.06.24.20138875
  5. Pollán M et al. Prevalence of SARS-CoV-2 in Spain (ENE-COVID): a nationwide, population-based seroepidemiological study. Lancet. 2020;396(10250):535-544. doi:10.1016/S0140-6736(20)31483-5
  6. Adamik B. et al. Estimation of the Severeness Rate, Death Rate, Household Attack Rate and the Total Number of COVID-19 Cases Based on 16115 Polish Surveillance Records. Available at SSRN: https://ssrn.com/abstract=3696786 or http://dx.doi.org/10.2139/ssrn.3696786
  7. Brett TS, Rohani P. Transmission dynamics reveal the impracticality of COVID-19 herd immunity strategies. Proc Natl Acad Sci U S A. 2020 Oct 13;117(41):25897-25903. doi: 10.1073/pnas.2008087117. Epub 2020 Sep 22. PMID: 32963094.
  8. Long COVID: let patients help define long-lasting COVID symptoms. Nature. 2020 Oct;586(7828):170. doi: 10.1038/d41586-020-02796-2. PMID: 33029005.
  9. Alwan NA, Burgess RA, Ashworth S, Beale R, Bhadelia N, Bogaert D, Dowd J, Eckerle I, Goldman LR, Greenhalgh T, Gurdasani D, Hamdy A, Hanage WP, Hodcroft EB, Hyde Z, Kellam P, Kelly-Irving M, Krammer F, Lipsitch M, McNally A, McKee M, Nouri A, Pimenta D, Priesemann V, Rutter H, Silver J, Sridhar D, Swanton C