The effect of strict lock down measures on Covid-19 seroprevalence rate and herd immunity

Abstract

Background: Covid-19 seroprevalence rates and serological tests are important tools in understanding the epidemiology of the disease and help in the fight against it. Seroprevalence rates vary according to the population studied and the test employed and they range from 0.133 to 25.7%. The purpose of this study is to assess the seroprevalence rate in a population of healthy blood donors living under strict lockdown measures in Jordan which has in total 71 confirmed cases per million population. Methods: Left over sera and plasma samples from 746 healthy blood donors were tested using a commercially available FDA approved kit having a specificity of 100%. External positive controls were used for validation. Results: More than 80% of the donors were men 18-63 year old and residing in the capital city of Jordan, Amman. All tested specimens were negative yielding a zero seroprevalence rate in this healthy blood donor population. Conclusion: Strict lockdown measures effectively limit intracommunity spread of the infection, however at the cost of lack of any acquired community immunity. Additionally the use of highly specific test is recommended in low prevalence setting.

Results from a survey in healthy blood donors in South Eastern Italy indicate that we are far away from herd immunity to SARS‐CoV‐2

“…10 In other geographical regions, serosurveys in healthy individuals demonstrated a very low rate of positivity for SARS-CoV-2. [11][12][13][14][15] In our study, we confirm a low rate of antibodies against SARS-CoV-2 on a group of blood donors from a geographical region with a moderate incidence (187 cases/100,000 inhabitants vs the national data of 390 infections/100,000 inhabitants); our results are at variance with those observed in other regions of Italy. In fact, a higher rate of anti-SARS-CoV-2 antibodies has been reported in studies conducted in a region with high incidence of infection, such as Lombardy, the most affected region in Italy, where the seroprevalence in blood donors was 5.2%, a number that is justified by the wide circulation of the virus in that area during the pandemic A limitation of our study is that the enrolled population (18-65 years old) is representative of only a part of the general population, since in Italy 22% of the individuals is aged >65 years (16) However, presented data are relevant in that they refer to the more acting/interacting group of the population, also important from a productive point of view.…”

Low prevalence of antibodies against SARS‐CoV‐2 among voluntary blood donors in Guangzhou, China

“…France (3%), 17 Italy (5.1%), 18 Denmark (1.8%), 19 and Jordan (0%). 20 In this study, although seven samples were reactive to the initial total antibodies test, no asymptomatic active COVID-19 infection was found because all seven BDs reactive for total antibodies were negative for the viral nucleic acid and IgM antibody against anti-SARS-CoV-2. In addition, only two samples (0.09%) were positive for IgA and IgG antibody tests.…”

Seroprevalence of antibodies to SARS-CoV-2 among blood donors in the early months of the pandemic in Saudi Arabia

“…The seroprevalence in this study, albeit conducted among blood donors who had no confirmed SARS-CoV-2 infection, was consistent with most findings from other studies of the prevalence of anti-SARS-CoV-2 antibodies among blood or plasma donors, or of stored samples, from January to June 2020. Notwithstanding the differences in study methods and SARS-CoV-2 transmission patterns between different areas, most of these studies found low levels of seroprevalence of 0% to 23% ( Erikstrup et al, 2020 , Gallian et al, 2020 , Grzelak et al, 2020 , Filho et al, 2020 , Ng et al, 2020 , Percivalle et al, 2020 , Sughayer et al, 2020 , Thompson et al, 2020 , Valenti et al, 2020 ).…”

“…For example, 0% seroprevalence was reported in Amman city, Jordan ( Sughayer et al, 2020 ); 0.1% in the San Francisco Bay Area, California, USA ( Ng et al, 2020 ); 0.9% (IgG) in 3 federal states (North Rhine-Westphalia, Hesse, and Lower Saxony) in Germany ( Fischer et al, 2020 ); 1.9% in Denmark ( Erikstrup et al, 2020 ); 2.7% in blood donors in the Netherlands ( Slot et al, 2020b ); 2.7% in 4 departmental areas in France ( Gallian et al, 2020 ); 3.0% in in two blood banks in Clermont and Noyon cities, Oise, France ( Fontanet et al, 2020 ); 3.2% in Scotland ( Thompson et al, 2020 ); 4.0% in the State of Rio de Janeiro, Brazil ( Filho et al, 2020 ); 7.1% in Milan metropolitan area, Lombardy, Italy ( Percivalle et al, 2020 , Valenti et al, 2020 ); and 8.5% (overall weighted adjusted) in England ( Erikstrup et al, 2020 , Gallian et al, 2020 , Grzelak et al, 2020 , Filho et al, 2020 , Ng et al, 2020 , Percivalle et al, 2020 , Sughayer et al, 2020 , Thompson et al, 2020 , Valenti et al, 2020 ).…”