Swedish Covid-19 Investigation for Future Insights


Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) first emerged in Wuhan in December 2019,1 and was quickly discovered to trigger the illness now named coronavirus illness 2019 (Covid-19). During 2020, the illness developed right into a large-scale pandemic, spreading to most international locations on this planet, together with coming into a second or third wave in lots of locations, with cumulative numbers of over 83 million instances and 1.8 million deaths reported globally through the first yr till finish of 2020.2 By the top of 2020, vaccines had been developed and vaccination campaigns have been initiated in a number of international locations, together with Sweden. The first Covid-19 case in Sweden was reported on 31 January 2020, and in parallel with Europe changing into the epicenter for the epidemic through the Spring of 2020, the illness quickly expanded in Sweden, inflicting extreme pressure on society and the healthcare system.3

It was clear on the time that analysis each within the brief and long run could be required, and the analysis communities in Sweden and internationally shortly equipped to answer the problem. The research described right here based mostly on Swedish knowledge was quickly designed as a large-scale effort to assemble a wealthy database for the research of Covid-19 epidemiologically in actual time, ie, with the requirement that knowledge could be recurrently and sufficiently regularly up to date. The significance of not solely specializing in Covid-19 sufferers was additionally acknowledged, making the inclusion of a big comparability cohort reflecting the overall inhabitants one other key asset.

Even towards the background of fast-track processes for moral approval and knowledge entry for Covid-19 analysis creating on the time,4 this has been fairly a posh process with out clear precedent within the Swedish registry knowledge ecosystem. This paper describes the database now established underneath the title of SCIFI-PEARL (Swedish Covid-19 Investigation for Future Insights – a Population Epidemiology Approach utilizing Register Linkage), and descriptions its analysis potential and utility within the ongoing and future phases of the pandemic.

Materials and Methods

Sweden, just like different Nordic international locations, has prime quality nationwide well being and inhabitants registers that may be linked with a excessive diploma of accuracy, offering a rare appropriate atmosphere for epidemiologic analysis. The Swedish Personal Identity Number (PIN; personnummer) uniquely linked to every particular person allows compilation and linkage of knowledge from various register knowledge to the identical people, with relative ease and with extraordinarily excessive accuracy.5 This SCIFI-PEARL research exploits the chance to assemble a novel massive database of people with Covid-19 plus a inhabitants cohort. After linkage, the database is pseudonymised, in line with normal procedures.

Study Population

Newly recognized people with Covid-19 from all the nation are included within the linked database on a recurrently up to date foundation, from totally different sources (Figure 1). This consists of all people with a constructive SARS-CoV-2 polymerase chain reactions (PCR) take a look at outcomes recognized from SmiNet,6 the nationwide register of notifiable communicable illnesses managed by the Public Health Agency of Sweden. In addition, sufferers who could not have a constructive take a look at registered however have been recognized by the healthcare system are included, eg, by Covid-19 ICD codes (ie, ICD-10 U07.1 = Covid-19, virus demonstrated; U07.2 = Covid-19, virus not proven) or related process codes on a nationwide foundation from the National Patient Register (NPR) for outpatient and hospitalized inpatient specialist care.7 Similarly, people recorded within the National Cause-of-Death Register (NCDR)8 as deaths as a result of Covid-19 are included. In addition, registration of take a look at consequence and ICD diagnoses made by a number of disease-specific nationwide high quality registers (NQRs) are scrutinized to determine extra potential Covid-19 sufferers with healthcare contacts associated to their explicit illness and subsequently captured in that register. Further, since there isn’t a nationwide protection for main care knowledge, healthcare contacts for Covid-19 in main care are captured on a regional foundation, for Western Sweden (Västra Götaland Region) and the Stockholm Region.

Figure 1 Structure of SCIFI-PEARL database. Included registers; identification of research inhabitants of COVID-19 sufferers (blue arrows) and normal inhabitants pattern (purple arrow); adopted by linkage to all registers for related knowledge from every register.

In addition, a normal inhabitants comparability group was obtained utilizing the nationwide Register of the Total Population (RTB) at Statistics Sweden,9 consisting of roughly 10% of the Swedish inhabitants (~1,000,000 people), based mostly on people of all ages resident in Sweden on 1 January 2020, by means of stratified random sampling in 20 age (5-year age classes) by 2 intercourse strata. This inhabitants can be utilized both in analyses as it’s, weighted to the Swedish inhabitants by means of sampling weights, or subsampled, as required for various kinds of statistical analyses and analysis questions.

Data Acquisition

To this mixed research inhabitants of people with Covid-19 from the entire Swedish inhabitants plus the ten% normal inhabitants comparability group, we linked various knowledge from a spread of registers with related info, to get a complete and detailed view of affected person historical past (Figure 1, Table 1). For sensible and moral causes the precise linkage is carried out by the National Board of Health and Welfare (NBHW), and the PIN for every topic is changed by a person research topic identifier, to pseudonymise the info.

Table 1 Source Registers and Types of Data Currently Available within the SCIFI-PEARL Study Database

The bulk of the info are from totally different nationwide registers. Date and reason behind dying are obtained from RTB and the NCDR. In-patient and specialist outpatient healthcare knowledge from 2015 onward, comprising a whole specialist care medical historical past for all people, are obtained from the National Patient Register (NPR). Cancer incidence knowledge from 2015 are extracted from the National Cancer Register (NCR). A whole drug historical past for pharmaceuticals from 2018 is obtained from the National Prescribed Drug Register (NPDR).10 Sociodemographic knowledge together with schooling, household state of affairs, revenue and occupational knowledge from 2018 onward are obtained from the Statistics Sweden Longitudinal Integrated Database for Health Insurance and Labour Market Studies (LISA; Longitudinell Integrationsdatabas för Sjukförsäkrings- och Arbetsmarknadsstudier).11 Finally, knowledge from a spread of nationwide high quality registers are included.12 These registers are nationwide in scope and supply detailed info on Covid-19 administration, in addition to related comorbidities and danger elements of significance for Covid-19 sufferers, with excessive granularity and element, on all recorded people with the respective underlying illness or situation coated by that individual NQR (Table 1). They embody registers for acute emergency care and intensive care (notably necessary for Covid-19 affected person knowledge) and the Swedish Register of Cardiopulmonary Resuscitation (SRCR) with knowledge extracted from 1 Jan 2020, in addition to registers for infectious illnesses, a number of heart problems registers, 2 respiratory illness registers, and the National Diabetes Register (NDR) with knowledge from 2015. The database can also be linked to the National Vaccination Register (NVR), which following pressing pandemic legislative adjustments in Dec 2020 captures info on vaccinations towards Covid-19 in Sweden.

In addition, some knowledge not obtainable on a consolidated nationwide foundation are included within the database for a extra detailed regional view. For Western Sweden (Västra Götaland Region) and the Stockholm Region, with a inhabitants of 4,902,162 out of 10,327,589 nationally (39.7%%), healthcare contacts and diagnoses recorded in main care are captured from 2015. For Western Sweden, an information supply with knowledge on SARS-CoV-2 testing from the beginning of the pandemic (each constructive and unfavorable exams), can also be included within the database, to offer knowledge on take a look at penetration over time within the inhabitants.

All knowledge are up to date with the latest knowledge from all included registers frequently, each few months, as required by the research aims and the evolution of the pandemic, in an agreed course of triggered every time by a request from the research crew to all registers. The advanced replace course of from extraction of knowledge at every knowledge supply to linkage and supply of a brand new full dataset is designed to take round 1 month.

Data Management

The research inhabitants choice, knowledge linkages and pseudonymisation of the info are managed in safe environments on the NBHW and Statistics Sweden. The pseudonymized analysis database thus produced and delivered is then housed on a devoted server on the Centre of Registers Västra Götaland, which has in depth expertise with massive databases, because it homes and manages plenty of NQRs. Data transfers use state-of-the-art encryption and the project-specific {hardware} is maintained with excessive safety ranges related for delicate private knowledge, with common backups. Access safety consists of disc encryption, community segmentation and two-level firewall safety with differential entry rights based mostly on venture position.


The research, together with common updates till no less than finish of 2025, has acquired moral approval from the Swedish Ethical Review Authority.

Research Objectives

The core preliminary analysis aims outlined within the venture plan are comparatively broad and canopy descriptive, analytical and predictive modeling analyses.

Primary Aims

  • To descriptively characterize people with Covid-19 (general, hospitalized, intensive care unit (ICU) handled, deaths, and in necessary subgroups) when it comes to sociodemographics, varied danger elements (eg, comorbidity, co-medication), geographic distribution, timing, and so forth. Further, describe how the epidemic and the traits of the affected affected person group change over time, ie, “pure historical past” of the epidemic in relation to the inhabitants.
  • To quantify the affect and significance of comorbidities (particularly respiratory and cardiovascular, diabetes, weight problems), severity of and co-medications for concomitant illness, sociodemographics, and different danger elements, in addition to protecting measures and vaccinations, on danger of varied endpoints. Some anticipated endpoints embody creating Covid-19, being hospitalized for Covid-19, emergency/ICU care, remedies, particular care, hospitalization period, prognosis, dying and in survivors research long-term outcomes as much as 3 years. Various research designs and strategies as applicable might be employed, together with case-cohort, case-control and interrupted time collection research designs, and machine studying strategies.
  • To develop, and periodically replace prediction fashions for Covid-19 incidence and prognosis, and consider how this impacts healthcare useful resource use, together with the necessity for ICU remedy. Use of machine studying strategies might be necessary right here.

Secondary Aims

Secondary goals will embody quickly upcoming analysis questions based mostly on main prevention and healthcare wants, and embody:

  • Treatment results of medicines and different healthcare interventions, together with novel indications for established remedies and vaccinations, and potential side-effects associated to Covid-19.
  • Resource use within the healthcare system, on the particular person stage, and at societal stage (hospital assets, measures, medicines, prices, and so forth.)
  • Study the effectiveness of vaccination applications and potential opposed reactions within the inhabitants.
  • Consequences of the covid-19 pandemic together with future vaccination applications on drug use, well being care and different societal capabilities within the inhabitants.
  • Other upcoming questions and data gaps from society, healthcare and the scientific neighborhood (if these are exterior the above specified points, may have extra supplemental moral software).

Current and Future Activities

A primary knowledge supply of all knowledge was compiled in October 2020. Data merging and knowledge administration, in addition to evaluation variable and evaluation database development, are carried out on an ongoing foundation. We have acquired three full knowledge updates by Spring 2021. The updating course of has thus been examined and located to be practical, and common updates of the research inhabitants and knowledge could now be thought of routine. Plenty of analysis analyses at the moment are in varied levels of completion.

Based on the primary knowledge supply, the variety of research topics and their age and intercourse distribution are described in Table 2 and Figure 2. As the info are up to date, the inhabitants comparability cohort (as sampled on 31 Dec 2019) will stay initially static, with a view to replace at appropriate intervals to the present Swedish inhabitants, whereas the variety of Covid-19 sufferers will develop successively with every knowledge supply.

Table 2 Study Sample for SCIFI-PEARL Based on Initial October 2020 Data Delivery, with Age and Sex Distributions

Figure 2 Age distribution of research topics in SCIFI-PEARL based mostly on preliminary October 2020 database for inhabitants comparability cohort, test-positive covid-19 sufferers and hospitalized covid-19 sufferers.

Currently, plenty of analysis tasks have been began at varied levels. The core venture crew has initiated collaborations with plenty of exterior researchers, and collaboration proposals from different exterior companions nationally and internationally are inspired. The research database is a worthwhile useful resource that must be used as broadly as possible for necessary analysis to offer epidemiological and scientific proof to learn sufferers, the healthcare system and society.

We are additionally exploring the potential to hyperlink the database to some present large-scale well-characterized population-based epidemiological research in Sweden which have extra detailed scientific and questionnaire knowledge on particular populations, such because the West Sweden Asthma Study (WSAS) and SCAPIS (the Swedish CArdioPulmonary bioImage Study). These potential spin-off tasks will probably require separate setup and ethics evaluate, however could present fascinating insights, additionally on a extra mechanistic stage.

An worldwide outlook can also be necessary. We have established collaboration with the Nordic COHERENCE venture,13 aiming to facilitate large-scale register-based observational analyses throughout a number of Nordic Covid-19 nationwide databases, particularly for analysis questions the place bigger pattern sizes are fascinating, or the place comparisons throughout totally different populations, societies or healthcare programs could also be related. The evaluation technique will construct on a Nordic frequent knowledge mannequin (CDM) and distributed analyses, retaining knowledge at every nation website to guard particular person knowledge. Other worldwide collaborations are additionally inspired.


The Covid-19 pandemic is a big concern globally in addition to in Sweden, given the tempo of unfold and breadth of well being impacts on the inhabitants stage, posing an enormous problem to international well being. A significant impediment to understanding, managing and stopping Covid-19 continues to be insufficient, non-transparent, and out-of-date Covid-19 knowledge because the pandemic progresses. Many scientists proceed to look for revolutionary sources and makes use of of real-world knowledge for complete and present Covid-19 analysis. Since data on Covid-19 is consistently evolving, population-based analysis at a nationwide scale is essential, utilizing the most recent, point-of-care knowledge that may be leveraged to help analysis and improvement. Carefully assembled and used, the high-quality nationwide register knowledge obtainable in Sweden will assist analysis immensely, for instance, to characterize danger sufferers, determine and quantify danger elements, develop machine studying instruments to foretell COVID-19 severity and mortality, and observe vaccination and pandemic developments, vital insights for driving care to highest-risk sufferers and higher managing the outbreak, with broad international applicability. We have subsequently assembled a repeatedly up to date database of Covid-19 sufferers and normal inhabitants comparator people.

Some learnings from this initiative are broadly related in a global setting. Assembling and accessing knowledge in actual time from many knowledge sources will be difficult and really time consuming as a result of course of, authorized and different elements – even in a rustic comparable to Sweden – and subsequently good planning is crucial. Plans for such efforts must be made in any nation that goals for higher future pandemic preparedness, tailor-made to the actual state of affairs in that space. It is especially necessary to pay shut consideration to native authorized frameworks when establishing processes for knowledge sharing. This is sadly not the final time there might be pressing want of scientifically sturdy knowledge on a brand new well being concern, and it will likely be important to plan upfront to have wealthy knowledge obtainable for analysis use when the necessity arises.

This initiative has a number of strengths. The distinctive PIN in Sweden permits for high-quality linkage of many registers, assembling wealthy knowledge for every particular person. Swedish nationwide healthcare registers and nationwide high quality registers are typically of very prime quality, with dependable knowledge. The full and correct nationwide inhabitants register (RTB) that’s regularly up to date and obtainable for sampling allows us to pattern basically all identifiable people with Covid-19 in Sweden in addition to a really massive stratified random pattern of normal inhabitants comparability topics that may present context and comparability for deliberate analyses. This can’t be simply executed exterior the Nordic international locations. The research has a big pattern measurement and we now have additionally in-built common updating of the database with new Covid-19 topics and present knowledge over time through the pandemic, to make sure optimum energy and knowledge availability.

The research builds on actual life scientific knowledge from a well being care system with basically equal entry to all residents in Sweden. Thus, unequal or biased testing/prognosis/hospital care for eg, price causes is a restricted downside. However, different elements comparable to useful resource limitations and prioritization, particularly throughout probably the most intensive pandemic phases, should still have an effect on entry to care, and must be adequately thought of to keep away from bias in any analysis carried out.

Potential weaknesses embody these frequent to most observational knowledge. Data high quality relies on the completeness and accuracy of the knowledge registered. There are inherent weaknesses associated to eg, ICD10 coding and the way in which totally different situations are labeled, recorded and grouped. Similar concerns apply to process and drug coding. Some knowledge are simply not obtainable, eg, regardless of a high-quality prescription drug register being obtainable, in-hospital drug remedy shouldn’t be available in Sweden. Register analysis is by its very nature retrospective within the sense that it depends on knowledge collected primarily for one other goal, which can have an effect on content material, accuracy, and completeness of knowledge. This may also be a power, eg, for inference and potential relevance, and avoidance of some sorts of bias. Finally, register knowledge most frequently is used for observational analysis, which, regardless of research designs – descriptive, case-cohort, case management and so forth. – could endure from residual bias even after use of standardization, weighting or adjustment to eradicate confounding, and subsequently as prime quality as potential of the underlying register knowledge is necessary.

A possible weak spot that must be thought of in research of COVID-19 is the uncertainty concerning who’s examined for Covid-19 and the way this impacts estimates of illness incidence or severity in numerous teams.14 Rich knowledge to assist deal with that is current in our research. It can also be clear that the likelihood of being contaminated varies throughout teams relying on eg, housing situations and social and behavioral elements, though to the extent that these will be captured within the database this might be taken under consideration or particularly studied. However, these weaknesses are current in all places in epidemiologic analysis on Covid-19 and should in lots of instances be much less outstanding in Sweden than in another international locations with higher socioeconomic variations and extra restricted entry to well being care. This can also be not distinctive for Covid-19. For nearly any illness there may be uneven prognosis with each over- and underdiagnosis, which varies by different elements. Similarly, most illnesses lack steady gold customary standards that may be utilized in scientific observe over time, and observational analysis should depend on the precise scientific diagnostic efforts and scientific actuality.


The SCIFI-PEARL (Swedish Covid-19 Investigation for Future Insights – a Population Epidemiology Approach utilizing Register Linkage) research cohort captures basically all Swedish residents with Covid-19 on an ongoing foundation, features a consultant normal inhabitants comparability cohort, and hyperlinks to a broad vary of nationwide and regional healthcare knowledge for a complete longitudinal view of the Covid-19 pandemic. By combining prime quality nationwide registers with brief time delay and steady repeated linkage updating, the venture will deliver well timed and internationally distinctive knowledge for epidemiological analysis on SARS-CoV-2. Broad analysis efforts are ongoing and additional collaborative efforts are invited. Finally, our expertise in establishing the venture and database carries necessary classes for constructing knowledge repositories elsewhere to deal with pressing well being issues.


The core research is at present financed by grants from the Swedish state underneath the settlement between the Swedish authorities and the county councils, the ALF-agreement (Avtal om Läkarutbildning och Forskning/Medical Training and Research Agreement) grant ALFGBG-938453 and from FORMAS (Forskningsrådet för miljö, areella näringar och samhällsbyggande/Research Council for Environment, Agricultural Sciences and Spatial Planning), a authorities analysis council for sustainable improvement, grant 2020-02828. Additional grants supporting totally different elements of ongoing analysis inside the research embody: the Swedish Heart Lung Foundation (20210030), Knut och Alice Wallenbergs Stiftelse/SciLifeLab (KAW 2021.0010), the Swedish Research Council (2021-05045, 2021-05450), and the Swedish Social Insurance Agency (FK 2021/011186).


Dr. Nyberg reviews prior employment at AstraZeneca till 2019, and possession of some AstraZeneca shares. Dr. Vanfleteren reviews grants and private charges from AstraZeneca, private charges from Novartis, GSK, Chiesi, Menarini, Pulmonx, Resmed, Boehringer, Verona Pharma, AGA Linde exterior the submitted work. Dr. Sundström reviews possession in firms offering providers to Itrim, Amgen, Janssen, Novo Nordisk, Eli Lilly, Boehringer, Bayer, Pfizer and AstraZeneca, exterior the submitted work. Dr. Gisslén reviews private charges from Gilead, private charges from GSK/ViiV, private charges from MSD, different from Gilead, different from GSK/ViiV, private charges from Biogen, private charges from Novocure, private charges from Amgen, private charges from Novo Nordisk, exterior the submitted work. Dr. Lindh, Dr. Santosa, Dr. Franzén, Dr. Wettermark, Dr Björck and Dr. Hammar don’t have anything to reveal.


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