key: cord-0263961-cxtzf5oe authors: fiore, j. r.; centra, m.; de carlo, a.; granato, m.; rosa, a.; de feo, l.; di stefano, m.; d ' errico, m.; lo caputo, s.; de nittis, r.; arena, f.; corso, g.; MARGAGLIONE, m.; SANTANTONIO, T. A. title: FAR AWAY FROM HERD IMMUNITY TO SARS-CoV-2: results from a survey in healthy blood donors in South Eastern Italy date: 2020-06-19 journal: nan DOI: 10.1101/2020.06.17.20133678 sha: 350230f6573bc488e5fd879e46ae3df1c39e550f doc_id: 263961 cord_uid: cxtzf5oe Here we present results from a survey on anti-SARS-CoV-2 seroprevalence in healthy blood donors from a low incidence COVID-19 area (Apulia region, South Eastern Italy). Among 904 subjects tested, only in 9 cases (0.99%) antibodies against SARS-CoV-2 were demonstrated. All the 9 seropositive patients were negative for the research of viral RNA by RT-PCR in nasopharyngeal swab. These data, along with those recently reported from other countries, clearly show that we are very far from herd immunity and that the containment measures are at the moment the only realistic instrument we have to slow the spread of the pandemic. Ospedali Riuniti University Hospital 24 Via Luigi Pinto 1 71100 Foggia (Italy) 25 Email jose.fiore@unifg.it 26 . CC-BY 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted June 19, 2020. . https://doi.org/10.1101/2020.06.17.20133678 doi: medRxiv preprint ABSTRACT 27 28 Here we present results from a survey on anti-SARS-CoV-2 seroprevalence in healthy blood donors 29 from a low incidence COVID-19 area (Apulia region, South Eastern Italy). 30 Among 904 subjects tested, only in 9 cases (0.99%) antibodies against SARS-CoV-2 were 31 demonstrated. All the 9 seropositive patients were negative for the research of viral RNA by RT-32 PCR in nasopharyngeal swab. 33 These data, along with those recently reported from other countries, clearly show that we are very 34 far from herd immunity and that the containment measures are at the moment the only realistic 35 instrument we have to slow the spread of the pandemic. 36 37 38 . CC-BY 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) The copyright holder for this preprint this version posted June 19, 2020. infections if some percentage of the population has immunity to it. When most of a population is 42 immune to an infectious disease, this provides indirect protection, or herd protection, to those who 43 are not immune (1) 44 There are two ways to achieve herd immunity: a large proportion of the population either gets 45 infected or gets a protective vaccine. Based on early estimates of SARS-CoV-2 infectiousness, it 46 should be likely needed at least 60-70% of the population to be immune to have herd protection (2). 47 However, more recently mathematical models suggest that lower thresholds could be enough to 48 place populations over the herd immunity threshold once as few as 43% (3) or even10-20% of its 49 individuals are immune. (4) 50 It is therefore important and urgent to evaluate the extent of circulation (and thus of immunity to) 51 Of SARS-CoV-2 in the general populations of affected countries because this information should 52 guide the extent of reduction or increasing of preventive measures such as social distancing etc. 53 Italy registered the first imported cases of infection in January 31 2020 and after one week the first 54 local case. After that, a dramatic burden of infections was diagnosed: 235.278 cases (with 33.964 55 deaths) as for June 8 2020, with main clusters in Northern Italy. As a whole, 390 56 infections/100.000 inhabitants. In Foggia (Apulia region, South Eastern Italy) the first case was 57 observed in March the 1st and as for June 8, 1162 cases were diagnosed with an incidence of 187 58 cases/100.000 inhabitants (5)). 59 Although the total number of diagnosed infections is moderate, we miss clear information regarding 60 the number of individuals in the general population that became immune, possibly acquiring the 61 virus with no or mild symptoms. 62 . CC-BY 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) The copyright holder for this preprint this version posted June 19, 2020. . https://doi.org/10.1101/2020.06.17.20133678 doi: medRxiv preprint Studies on blood donor cohorts are useful to evaluate the prevalence, incidence and natural course 63 of infectious diseases in the general population and may thus help to assess both the viral 64 circulation and the evolution of the COVID-19 outbreak. 65 We therefore studied a group of healthy blood donors from Foggia province for the presence of IgM 66 and IgG to antibodies to SARS-CoV-2 to examine the circulation of the virus in the general 67 population three months after the local start of the epidemic. 68 69 . CC-BY 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted June 19, 2020. University Hospital (Foggia, Italy) were included in the study and subjected to the search for anti-85 SARS-CoV-2 antibodies, in the period May1-31 2020. In the case of positivity, subjects were re-86 called and RT-PCR for detection SARS-CoV-2 from nasopharyngeal swabs was performed. 87 88 . CC-BY 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted June 19, 2020. CC-BY 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted June 19, 2020. (Table 1) The disease-induced herd immunity threshold for SARS-CoV-2, according to various 144 epidemiologists, is believed to be around 60 to 70 percent (2) More recently, some researchers have 145 reported lower thresholds: from 43% to just 10 to 20% of the population (3, 4) , suggesting that we 146 could reach herd immunity thresholds by natural infections in the setting of COVID-19 pandemic. 147 Recently, data from Spain, France and Italy (7-9) countries that adopted strict lockdown measures 148 indicate a very low seroprevalence in the general population (4.4%, 5% and 7.1%, respectively). 149 Noteworthy, even in Sweden, a country that decided for a herd immunity strategy, with very light 150 restrictions on daily life, antibodies to SARS-CoV-2 were detectable in only 7.5% of the general 151 population in Stockholm (10). 152 . CC-BY 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted June 19, 2020. . https://doi.org/10.1101/2020.06.17.20133678 doi: medRxiv preprint In other geographical regions, serosurveys in healthy individuals demonstrated a very low rate of 153 positivity for SARS-CoV-2 (11) (12) (13) (14) (15) . 154 In our study, we confirm a low rate of antibodies against SARS-CoV-2 on a group of blood donors 155 from a geographical region with a moderate incidence (187 cases/100.000 inhabitants vs the 156 national data of 390 infections/100.000 inhabitants). 157 A limitation of our study is that the enrolled population (18-65 years old) is representative of only a 158 part of the general population, since in Italy 22% of the individuals is aged >65 years (16) 159 However, presented data are relevant in that they refer to the more acting/interacting group of the 160 population, also important from a productive point of view. 161 Certainly, we are far away from herd immunity and even from the more optimistic projections of 162 threshold (10 to 20% of the population) to adopt more relaxed strategies. 163 In conclusion, strengthening herd immunity to control the COVID-19 epidemic is not a viable 164 option as large numbers of people are expected to become infected and many may die from 165 COVID-19. Preventive measures, including physical distancing, remain essential to contain the 166 spread of infection until herd immunity can be safely acquired with the vaccine. Health authorities 167 should take in account these considerations when facing the public health measures to be adopted 168 throughout the COVID-19 transition phases. CC-BY 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) The copyright holder for this preprint this version posted June 19, 2020. . https://doi.org/10.1101/2020.06.17.20133678 doi: medRxiv preprint . CC-BY 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) The copyright holder for this preprint this version posted June 19, 2020. . https://doi.org/10.1101/2020.06.17.20133678 doi: medRxiv preprint Estimating 203 the burden of SARS-CoV-2 in France SARS-CoV-2 207 seroprevalence trends in healthy blood donors during the COVID-19 Milan outbreak Seroprevalence rate in healthy blood donors from a community under strict lockdown 217 measures 218 medRxiv 2020.06.06 at 221 all. Seroprevalence of SARS-CoV-2 in Hong Kong and in residents evacuated from Hubei 222 province, China: a multicohort study Seroprevalence of IgG 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 . CC-BY 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted June 19, 2020. is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted June 19, 2020. . https://doi.org/10.1101/2020.06.17.20133678 doi: medRxiv preprint