key: cord-340738-2pufvc67
authors: AbdAllah, Mohamed; Cordie, Ahmed
title: Herd-immunity against COVID-19: Is it enough to stop a second wave?
date: 2020-11-12
journal: New Microbes New Infect
DOI: 10.1016/j.nmni.2020.100811
sha: 
doc_id: 340738
cord_uid: 2pufvc67

Herd-immunity is a defensive strategy against COVID-19. Many reports doubt the efficacy and durability of the “post-infection” immunity, therefore, countries should not rely on herd-immunity for protection against the further-coming wave of COVID-19.

Medical Research Division, National Research Center, Giza, Egypt.

Endemic Medicine Department, Faculty of Medicine, Cairo University, Cairo, Egypt.

Keywords: COVID-19; Second wave; Past-infection; immunity; Herd-immunity • This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

• The Authors declare that there is no conflict of interest' Herd-immunity is a defensive strategy against COVID-19. Many reports doubt the efficacy and durability of the "post-infection" immunity, therefore, countries should not rely on herd-immunity for protection against the further-coming wave of COVID-19.

Dear Editor, Humanity faces its greatest challenge in the last 100 years as the outbreak of coronavirus disease 2019 (COVID-19) caused more than 17 million confirmed cases all over the world [1] .

About eighty percent of COVID-19 cases are asymptomatic or presented with mild symptoms. Minor cases will progress to respiratory distress which may necessitate mechanical ventilation [2] . Host immunological response plays an important role in determining the outcome of infection [3] . Patients with severe COVID-19 usually have a higher level of interleukins 6, 10 and tumor necrotic factor α and fewer CD4+ and CD8+ T cells than mild cases [4] .

Many reports discussed the durability of "Post-infection" immunity after COVID-19 infection. The neutralizing antibodies (Nab) that are produced by B cells after infection were successful in preventing reinfection in animal models and that was the concept of using convalescent plasma as a potential therapy for COVID-19 [5] .

Unfortunately, using convalescent plasma as a therapy for COVID-19 didn't achieve success when added to the standard of care of COVID-19 patients in real life studies. Short-lasting humoral immune response and the required high Nab titre (above 1:640) are main limiting factors for success. These data raise suspicion concerning the efficacy of "post-infection" immunity and subsequently the herd immunity in controlling COVID-19 [6, 7] .

Using herd-immunity as a defense strategy against COVID-19 has been adopted by many countries.

Herd immunity refers to the indirect protection from infection conferred to susceptible individuals when a sufficiently large proportion of immune individuals exist in a population [8] . A trial of implementing J o u r n a l P r e -p r o o f this strategy was done in the United Kingdom at the beginning of the pandemic but it wasn't successful [9] . Additionally, countries who lifted their community preventive measures depending on herdimmunity begin to report a second rise of cases. Studies showed that the estimated proportion of the total population infected varies between the countries from less than 1% in Norway, Germany, and Austria to 8% in Belgium which is too low to achieve herd-immunity [10] .

Lifting of COVID-19 community preventive measures makes these countries vulnerable to suffering from what is called " The second wave of COVID-19" [11] . Countries should not rely on herd-immunity for protection against the second wave of COVID-19. Effective community preventive measures with optimization of screening and treatment are the cornerstones for success.

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Herd Immunity: Understanding COVID-19. Immunity

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