|Year : 2020 | Volume
| Issue : 2 | Page : 163-168
An insight into the encountered challenges and performances of a hospital-based blood transfusion service in Eastern India in the light of COVID-19 pandemic
Sudipta Sekhar Das, Rathindra Nath Biswas, Rafique Uz Zaman
Department of Transfusion Medicine, Apollo Gleneagles Hospitals, Kolkata, West Bengal, India
|Date of Submission||25-Jul-2020|
|Date of Decision||23-Sep-2020|
|Date of Acceptance||30-Sep-2020|
|Date of Web Publication||13-Nov-2020|
Sudipta Sekhar Das
Department of Transfusion Medicine, Apollo Gleneagles Hospitals, Kolkata, West Bengal
Source of Support: None, Conflict of Interest: None
Background: Every pandemic elaborates its own challenges that should be managed meticulously through proper initiative and planning, following existing guidelines and through population education. We encountered various challenges in our blood center which significantly affected the blood inventory and blood supply. Here, we share our experiences of managing blood donations, blood inventory, staff adequacy, and blood wastages in the light of COVID-19 pandemic. Methods: The retrospective study was performed from January 1, 2020, to June 30, 2020, that included major activities in a blood center. The initial 3 and later 3 months were considered as the pre-COVID and COVID periods, respectively. Data related to various affected parameters were retrieved, analyzed, and compared with the pre-COVID period. Results: The drop in blood donation, blood component preparation, and blood issue in the COVID-period was observed to be 51.2%, 49.1%, and 49.8%, respectively. Mean total blood donation time and turnaround time of blood issue in the COVID period were found to be statistically significant (P < 0.05). The COVID period observed increase wastages of blood components (P = 0.007). The mean number of staff per day in the COVID period was 9.67 as compared to 18.3 staff in the pre-COVID period (P = 0.040). The mean work time per staff per day in the COVID period was calculated to be 10.77 h (P = 0.029). The major causes of failure to donate blood were fear of COVID infection and lack of transportation. Conclusions: All blood centers including ours have observed an acute reduction in blood donation and blood transfusion. All centers should collectively follow set guidelines and develop plan strategically to respond to the challenges generated in this pandemic. Moreover, blood transfusion should be more rationalized and the practice of first in, first out method should be followed to prevent blood wastages.
Keywords: Blood donation, blood transfusion service, blood wastage, COVID- 19, pandemic
|How to cite this article:|
Das SS, Biswas RN, Zaman RU. An insight into the encountered challenges and performances of a hospital-based blood transfusion service in Eastern India in the light of COVID-19 pandemic. Glob J Transfus Med 2020;5:163-8
|How to cite this URL:|
Das SS, Biswas RN, Zaman RU. An insight into the encountered challenges and performances of a hospital-based blood transfusion service in Eastern India in the light of COVID-19 pandemic. Glob J Transfus Med [serial online] 2020 [cited 2021 Mar 6];5:163-8. Available from: https://www.gjtmonline.com/text.asp?2020/5/2/163/300636
| Introduction|| |
The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has caused a devastating outbreak killing millions of people globally. The World Health Organization (WHO) declared the SARS-CoV-2 outbreak as a pandemic and named it COVID-19. Significant morbidities and mortalities have been observed in India affecting almost all states and districts. The previous global pandemics greatly enhanced the knowledge of preparedness in health-care services including the blood transfusion services (BTS). However, every pandemic elaborates its own challenges that should be managed meticulously through proper initiative and planning, following existing guidelines and through population education. The role of BTS in a pandemic depends on the type of pandemic, potentiality of community spread and the risk of transfusion transmissibility and cost-effectiveness of blood safety interventions.
The presence of SARS-CoV-2 RNA in blood during the presymptomatic period or asymptomatic infections remains to be established. Huang et al. reported that among the first 41 cases of COVID-19 admitted to hospitals in Wuhan, SARS-CoV-2 RNA was detected in six patients. To mitigate the risk of transfusion-transmission of SARS-CoV-2 if any through blood donation the National Blood Transfusion Council (NBTC) of India has furnished proper measures and guidelines.
In a recent study, 7 donors were identified as COVID-19 confirmed cases after blood donation. Where 1 recipient expired due to causes unrelated to COVID-19, the other 8 recipients have not developed any symptoms related to COVID-19.
A significant reduction in blood donations have been observed during previous viral outbreaks and the current COVID-19 pandemic is not different. The major causes of such crisis are (a) existence of fear among healthy population to get infected in hospitals, blood centers or during transportation, (b) failure to reach blood centers due to essential national lockdown, and (c) reluctant to conduct voluntary blood donation camps in view of risk of community spread. In addition various challenges such as staffing, consumables, blood inventory, donor attendance, and blood wastages have been observed in BTS during this COVID-19 pandemic.
Ours being a 750 bedded tertiary care hospital with a dedicated BTS, we encountered various challenges in the on-going COVID-19 pandemic which significantly affected the blood inventory and their supply to needy patients. Here, we share our experiences of managing blood donations, blood inventory, staff adequacy, and blood wastages in our BTS in the light of COVID-19 pandemic.
| Patients and Methods|| |
The retrospective study was performed from January 1, 2020, to June 30, 2020, that included major activities in a BTS namely blood donation, component preparation, issue of blood/blood component, and other quality-related works. The 6 months' study was divided into two periods where the initial 3 months were considered as the pre-COVID period and the later 3 months as COVID period. Data related to various BTS parameters which were affected in the COVID pandemic were retrieved, analyzed, and compared with the pre-COVID period.
Donor eligibility criteria for whole blood (WB) and single-donor platelets (SDP) donations were followed as per departmental standard operating procedures (SOP) in accordance with the dug and cosmetics act 1940 and rules 1945 therein. Moreover, in the light of COVID pandemic and to ensure optimal donor, staff, and donor safety guidelines provided by NBTC were strictly followed and executed. Briefly social distancing, masking, hand hygiene, and cough etiquette were maintained strictly and ethically. Alternate seats/donor beds were kept vacant with proper signage in understandable languages. Colored circles drawn or fixed on floor helped to maintain social distancing more effectively. An extra questionnaire with pertinent questions related to donor travel history, contact history, and COVID-19 symptoms was developed to exclude the at-risk donors. Proper personal protective equipment was used by BTS staff as per the organization policy and guidelines enacted by the Government of India. All donors were educated and advised to contact the BTS in case of any post donation illness including signs and symptoms of COVID-19 or in case of close contact with COVID-19. To enhance blood safety all blood donors on the 14th day of donation were personally contacted over telephone asking their well-being and health status. All such communication were documented in the donor card and signed by the BTS doctors. Donors with health issues were guided accordingly. Blood components namely packed red blood cells (PRBC) and plasma units were quarantined for 14 days before issue. However, platelet (PLT) concentrates due to short shelf life were issued within 3–5 days. For any donor complaining of illness suspicious of COVID-19, the blood components were recalled and discarded as per SOP.
As per SOP, all WB units were separated into blood components that included PRBC, fresh frozen plasma (FFP), random donor PLTs (RDP), cryoprecipitate (Cryo), and cryo-poor plasma. Data and details of WB and SDP donation, component preparation, blood issue, parameters of quality indicators, and patient occupancy were retrieved from the hospital information system and BTS registers. Shift-wise staffing per day (24 h) and work time per staff per day were obtained from the hospital time office management system which is a dedicated software managing staff attendance. Due to poor donor attendance in the COVID period, those voluntary donors who timely and religiously used to visit the BTS for blood donation were contacted over telephone. Donors who were reluctant to donate due to one or the other factors were documented and analyzed.
This study has been cleared by the institutional review board vide letter no 2020/05/025328A, dated 18.5.2020.
Statistical analysis was done using the SPSS statistical package (IBM, 2015, Armonk, New York, USA). All results were calculated as mean ± standard deviation and a “P” < 0.05 was considered statistically significant. Mean values were compared using the paired Student's t-test as appropriate.
| Results|| |
The present study observed a total of 4295 WB and 104 SDP donations. Where 2878 WB and 78 SDP were collected in the pre-COVID period; the COVID period observed 1417 WB and 26 SDP donations (P < 0.05). Accordingly, blood components prepared and issued for transfusion in pre-COVID period were 8090 units and 5386 units respectively which were significantly higher compared to only 4117 and 2706 units respectively in the COVID period (P < 0.03) [Figure 1]. The drop in blood donation, blood component preparation, and blood issue in the COVID-period was observed to be 51.2%, 49.1%, and 49.8%, respectively.
|Figure 1: Blood donation, component preparation, and blood transfusion in pre-COVID and COVID period|
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[Figure 2] describes the parameters related to quality indicators in the BTS in both the groups. Comparing the pre-COVID and COVID periods we observed no significant differences in the total number of donor adverse reaction (P = 0.477), donor deferral (P = 0.093), and transfusion-related patient adverse reaction (P = 0.183). However, the total donation time when compared between the pre-COVID and COVID periods was found to be statistically significant (44.7 min vs. 54.3 min, P = 0.015). The frequency of transfusion transmitted infection considering all the five mandatory markers was calculated to be 1.12% and 0.89% respectively in the pre-COVID and COVID periods (P = 0.097). In addition no anti-HIV reactivity was noted among the 1417 WB donations in the COVID period. The COVID period observed a high incidence of PRBC and RDP wastages. As high as, 143 units of blood components were discarded in the COVID period as compared to only 47 units in the pre-COVID period (P = 0.007). Where the PRBC wastage in the pre-COVID period was 2.4% only, it was 54.9% in the COVID period. The major cause of wastage in the COVID period was nonutilization which led to expiry of the product (90.2%). While calculating the mean turnaround time (TAT) of blood issue in the COVID period, it was observed to be 40.7 min which was significantly lower than the mean TAT observed in the pre-COVID period (58.3 min) (P = 0.036). Calculating the mean number of staff per day in BTS in both the periods, the number in the COVID period was observed to be 9.67 as compared to 18.3 staff in the pre-COVID period (P = 0.040). The mean work time per staff per day in the COVID period was calculated to be 10.77 h as compared to 8.13 h in the pre-COVID period (P = 0.029). A total of 778 voluntary donors were recalled for donation in the COVID period. Six hundred and sixty (84.8%) of them failed to donate due to various factors. The major causes of failure were found to be fear of COVID infection (45.6%) and lack of transportation (24.1%) [Table 1].
|Figure 2: Quality indicators in blood transfusion services in pre-COVID and COVID period|
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|Table 1: Factors affecting voluntary blood donor attendance in blood transfusion service (N=660)|
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| Discussion|| |
The COVID-19 pandemic has adversely affected the BTS globally. Almost all BTS including ours have observed an acute reduction in staff attendance, blood donation, and blood transfusion with an increase in blood wastages.,, The threat to the blood supply is not SARS-CoV-2 itself but also the unintended consequences of social distancing on blood donation drives. With mass cancellation of schools, colleges, business establishments, and large employment campuses many blood donation camps have to be cancelled. In addition, blood centers have been reluctant to conduct voluntary blood donation camps in view of the risk of community spread of the virus and prohibition of mass gatherings by the Government. In the same time cancellation of elective surgeries and procedures, suspension of organ transplantation program including stem cell transplantation and poor attendances in thalassemia, sickle cell, onco-hematology, and medical oncology clinics have reduced the blood utilization thereby increasing the blood wastage.
The WB and SDP donations in the present study dropped by 51.2% and 66.7%, respectively. Where authors in Saudi Arabia observed a mean WB donation of 175 units per month in the COVID period with a notable drop of 40.4%; a similar drop of 64% was reported by Raturi and Kusum., During the SARS epidemic in 2003, a 60% decline of blood donors were reported in Singapore. Similarly, during the influenza pandemic in 2009, 10%–30% fewer blood donations were observed worldwide. In the current COVID-19 pandemic donor attendance in the USA and Canadian blood services fell by 10%–30% and 30%, respectively. The authors also commented that in the early stages of the pandemic this trend of poor blood donation was compensated by a reduction in demand for blood because of decrease patient footfalls in the hospitals for treatment.
On contacting the voluntary donors telephonically we observed that 84.8% of them failed to attend the BTS mainly due to two factors (a) fear of getting COVID infection in the hospital/blood bank and (b) lack of transportation due to national lockdown. Another interesting cause of failure (9.8%) to donate blood in the pandemic was a fear in decrease of self-immunity after blood donation [Table 1]. Failure to donate blood in the COVID period due to fear of COVID infection was also described by previous authors.,, As the primary sources of donated blood are direct donation (mainly patients' relatives), voluntary nonremunerated donors, and mobile blood drives therefore patients' relatives mainly contributed to the blood inventory during the COVID period (68.3%).
Adequate efforts have been taken by state and national government to increase the blood inventory through public appeals to donate blood and by ensuring voluntary donors that blood donation is regarded as a permitted activity during lockdown.,, Despite constant donor motivation and education the COVID period witnessed only 449 (31.7%) voluntary donations. We observed that hospital employees form a vital voluntary donor base in any pandemic because they are easily available, have experience of blood donation and are very much aware of the blood crisis. Of the 449 voluntary donations, 72.8% donors were found to be hospital staff and doctors. All donors followed the BTS advices and maintained social distancing, masking, hand hygiene, and cough etiquette adequately and judiciously. No donor complaints were received as a result of long donation time. The mean donation time in COVID period was found to be 54.3 min and delays were primarily observed in the registration and donor screening sections. The main causes of such delay were (a) maintenance of social distancing, (b) prevention of donor crowding, and (c) poor staffing. No significant differences were noted in the frequency of donor deferral and donor adverse reaction in the COVID period when compared to the pre-COVID times. We also observed that blood donation staffs were concerned about exposure from asymptomatic donors or donors who concealed facts related to high COVID risks. The present study witnessed 13 (29.5% of all deferral) at-risk donors who were deferred due to positive history of travel or fever in the past 28 days. With a reduction in blood donation in the COVID period a proportionate drop of 49.1% was observed in component preparation. Adequate staffing has been a challenge faced in the COVID period. To ensure that hospitals and associated healthcare facilities are adequately staffed, with respect to numbers of personnel and required competencies, to deliver quality care and perform other hospital services in outbreaks the WHO has furnished guidelines on “Hospital preparedness for epidemics.” On the one hand, the BTS has the responsibility to save staff from infection; on the other hand, adequate workforce is needed for the routine and emergency works. We observed a mean staffing of 9.67/day in the COVID period which was significantly lower than the manpower per day calculated in the pre-COVID period. To obtain smooth running of the blood donation procedures workforce in this area was maintained optimally. However, provision of hospital transportation facility in the lockdown period and arrangement of accommodation and food for staff in the hospital premises helped in better running of the hospital including the BTS. In addition, the BTS restricted the staffing to prevent the risk of exposure and subsequent illness. Due to less staff per day, the mean work time per day per staff was calculated to be 10.77 h in the COVID period.
A pandemic leads not only to the deferral of nonurgent interventions, but also to the shielding of patients who are at increased risk of infection or having severe COVID-19. Patients might be reticent to attend health-care facilities, even for potentially serious symptoms. These changes in behavior have resulted in a substantial reduction in demand for all blood components., Each hospital and BTS should establish appropriate mitigation strategies if blood shortages are anticipated., A decrease in blood transfusion was observed in the COVID period. Only 2706 blood components were issued for transfusion which included 1415 units of PRBC, 386 units FFP, 751 units RDP, 129 units Cryo, and 25 units of SDP. Despite reduced blood inventory all in-patients received adequate dose of blood components. Due to low patient occupancy in the hospital during the COVID period, blood utilization dropped by 49.8%. Moreover, the national lockdown and pandemic have observed a reduction in the footfalls of the chronically transfused patients such as thalassemia, onco-hematology, and nephrology (dialysis) patients. Only 69 units of PRBC were transfused to 57 thalassemia patients in the COVID period against 207 PRBC units to 138 such patients in the pre-COVID time. A drop in 58.7% thalassemia admission was observed in the COVID period. Likewise, reduction in blood transfusion in onco-hematology, dialysis unit, intensive care units, medical oncology, gastroenterology, and cardiac sciences was calculated to be 65.7%, 60.3%, 48.7%, 48.4%, 52.4%, and 65.9%, respectively. Literature suggests that an increased need for blood components during a pandemic is highly unlikely and there may be a decrease in the blood demand as health-care capacity is shifted towards providing the basic health-care support, and nonurgent clinical interventions are usually deferred. It is estimated that demand for red cells decrease by 5%–25%, frozen and fractionated products by 0%–10%, with little or no change in PLT demands., Previous authors also reported reduction in both the demand as well as issue of blood units in the COVID pandemic. A blood component wise reduction of 14%, 11%, and 1.6% for PRBC, FFP, and PLT, respectively, was observed by Raturi and Kusum amid the COVID-19 outbreak.
Proper inventory management should be implemented in any pandemic to reduce the wastage of blood and blood components. According to the WHO, during the early stages of the pandemic when the population is still relatively unaffected, it is useful to boost blood stocks in anticipation of shortage later. The first in, first out (FIFO) policy should be strictly followed after verifying the inventory physically every day. In addition, the NBTC guides that blood and blood components with near expiry or excess of particular blood group units should be distributed to nearby other blood centers with special government permission for transportation in lockdown. We also suggest that clinicians should be educated and motivated to use nonidentical but compatible blood group components in place of identical groups. Moreover, SDP should be prepared from voluntary donors to mitigate the shortages in PLT concentrates. A significant wastage of blood component was noted in the COVID period (P = 0.007). The wastage rate of blood components was calculated to be 3.47%. Where wastage of 1 PRBC unit was observed in the pre-COVID period; the COVID period witnessed as high as 79 PRBC units discarded. Majority of the wastages of blood component was found in later half of April and first half of May 2020 because of the mandatory national lockdown leading to poor occupancy. A wastage rate of 2.39% was also reported by Raturi and Kusum. As low as 23.3% mean occupancy was observed in April 2020 and this gradually increased to 46.7% and 64.2% in May and June 2020 respectively which subsequently reduced the wastages.
Previous authors have emphasized shortages of all essential consumables required in a BTS due to the nationwide lockdown and banning of domestic and International flights. We encountered shortages in sanitizing agents, medical masks, and gloves during the initial weeks of lockdown. Shortages of consumables in our BTS were observed in the first 2 weeks of April 2020 due to lack of staff and transportation in the suppliers end. However, we assume that BTS situated in rural or suburban areas may encounter shortages of consumables for a longer period. Decreased blood donation and patient occupancy in the COVID period also reduced the number of overall laboratory testing per day in the BTS. We observed that the buffer stock of consumables played a vital role in the smooth function of the BTS especially in the initial days of lockdown.
Another follow-up challenge was the quarantine of blood units for 14 days particularly in time of blood crisis. This has been proved to be a good BTS practice because 2 donors reported postdonation illness related to COVID-19 after 9 and 13 days, respectively. Although they were negative for COVID-19 but to enhance blood safety the blood components were discarded as per SOP. In a way, the communication with blood donors on the 14th day of donation was found to be encouraging and may be a method of blood safety enhancement in BTS during a pandemic. Although transfusion transmitted SARS-CoV-2 has not been yet established, we anticipate that routine blood donor screening for anti-SARS-CoV-2 antibody would provide an additional layer of blood safety.
A study from the USA found a 2.8% seroprevalence of SARS-CoV-2, after adjusting for sensitivity and specificity of the test and population demographics. Other unpublished data exist on the prevalence of anti-SARS-CoV-2 antibody among blood donors. Two unpublished studies found seroprevalences of 1.7% and 2.7% among blood donors in Denmark and the Netherlands, respectively., Moreover, Filho et al. reported an overall antibody prevalence of 4% in 2857 Brazilian blood donors. We investigated 181 blood donors for anti-SARS-CoV-2 immunoglobulin G antibody in our BTS as part of product evaluation study and observed seroprevalence in 8 (4.4%) donors (unpublished data).
| Conclusions|| |
We conclude that the COVID-19 pandemic has contributed various challenges in the BTS globally. We at our blood center encountered the following challenges in the current pandemic:
- Apprehension and fear among voluntary donors
- Reduced blood donation
- Poor blood and blood component inventory
- Low blood utilization
- High blood and blood component wastage
- Low staff attendance.
Therefore, we suggest that all BTS should collectively follow set guidelines as mandated by national and international authorities and develop plan strategically to respond to the challenges generated in this pandemic. As the knowledge of COVID-19 is evolving almost daily and people globally are under stress, panic, and fear therefore proper donor education and efficient communication are the roads to overcome the current blood crisis. Moreover, BTS should develop SOPs related to various blood bank activities including blood donor management in the light of COVID-19 pandemic. In the same time with the global shortages of blood and blood components, blood transfusion in patients should be more rationalized and the practice of FIFO method should be followed more strictly to prevent wastages of precious resources. In addition, the concept of “doing more with less” in any pandemic can favorably balance the demand-supply chain.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
| References|| |
Network AP. Novel Coronavirus (SARS-CoV-2); Expected Challenges and Risks to Blood Safety; 2019.
Huang C, Wang Y, Li X, Ren L, Zhao J, Hu Y, et al
. Clinical features of patients infected with 2019 novel coronavirus in Wuhan, China. Lancet 2020;395:497-506.
Kwon SY, Kim EJ, Jung YS, Jang JS, Cho NS. Post-donation COVID-19 identification in blood donors. Vox Sang 2020. DOI: 10.1111/ vox.12925. (published online April 2) Available from: http://dx.doi.org/10.1111/vox.12925
Dhiman Y, Patidar GK, Arora S. Covid-19 Pandemic Response to Challenges by Blood Transfusion Services in India: A Review Report, ISBT Science Series; 2020. Available from: https://doi.org/10.1111/voxs.12563
. [Last accessed on 2020 Jul 05].
Malik V. Drugs and Cosmetics Act, 1940 and Rules 1945 There in Amended up to the 31st
December. India: Eastern Book Company; 2016.
Gehrie EA, Frank SM, Goobie SM. Balancing supply and demand for blood during the COVID-19 pandemic. Anesthesiology 2020;133:16-8.
Raturi M, Kusum A. The blood supply management amid the COVID-19 outbreak. Transfus Clin Biol 2020;27:147-51.
Teo D. Blood supply management during an influenza pandemic. ISBT Sci Ser 2009;4:6.
Pagano MB, Hess JR, Tsang HC, Staley E, Gernsheimer T, Sen N, et al
. Prepare to adapt: Blood supply and transfusion support during the first 2weeks of the 2019 novel coronavirus (COVID-19) pandemic affecting Washington State. Transfusion 2020;60:908-11.
Stanworth SJ, New HV, Apelseth TO, Brunskill S, Cardigan R, Doree C, et al
. Effects of the COVID-19 pandemic on supply and use of blood for transfusion. Lancet Haematol 2020;7:e756-64.
Gader AG, Osman AM, Al Gahtani FH, Al Gahtani FH, Farghali MN, Ramaden AH, et al
. Attitude to blood donation in Saudi Arabia. Asian J Transfus Sci 2014;5:121.
Ljungman P, Mikulska M, de la Camara R, Basak GW, Chabannon C, Corbacioglu S, et al
. The challenge of COVID-19 and hematopoietic cell transplantation; EBMT recommendations for management of hematopoietic cell transplant recipients, their donors, and patients undergoing CAR T-cell therapy. Bone Marrow Trans 2020. DOI:10.1038/s41409-020-0919-0. (published online May 13). Available from: http://dx.doi.org/10.1038/s41409-020-0919-0
Hussain FA, Njoku FU, Saraf SL, Molokie RE, Gordeuk VR, Han J. COVID-19 infection in patients with sickle cell disease. Br J Haematol 2020;189:851-2.
Yazer M, Pagano MB, Cho D, Lin Y. Vox Sanguinis International Forum on transfusion services about response to COVID-19. Vox Sang 2020;115:536-42. doi: 10.1111/vox.12943.
Guidelines for National Blood Transfusion Services: Maintaining a Safe and Adequate Blood Supply in the Event of Pandemic Influenza, World Health Organization. Available from: https://www.who.int/water_sanitation_health/en/
[Last accessed on 2020 Oct 28].
Bendavid E, Mulaney B, Sood N, Shah S, Ling E, Bromley-Dulfano R, et al
. COVID-19 antibody seroprevalence in Santa Clara County, California. medRxiv 2020. DOI: 10.1101/2020.04.14.20062463. Available from: https://doi.org/10.1101/2020.04.14.20062
[Last accessed on 2020 Apr 30].
Erikstrup C, Hother CE, Pedersen OBV, Molbak K, Skov RL, Holm DK, et al
. Estimation of SARS-CoV-2 infection fatality rate by real-time antibody screening of blood donors. medRxiv 2020. DOI: 10.1093/cid/ciaa849. Available from: https://doi.org/10.1101/2020.04.24.2007529117
. [Last accessed on 2020 Jun 19].
Slot E, Hogema BM, Reusken CB, Reimerink JH, Molier M, Karregat JH, et al
. Herd immunity is not a realistic exit strategy during a COVID-19 outbreak. Res Sq 2020. DOI: 10.21203/rs.3.rs-25862/v1. Available from: https://doi.org/10.21203/rs.3.rs-25862/v1
. [Last accessed on 2020 Apr 29].
[Figure 1], [Figure 2]