Results
In the first half of 2020, the total number of articles published on PubMed equaled 858,641. Overall, we identified 27,815 articles on COVID-19, which constitutes 3.24% of all publication in this time. Among those we found 18,225 (65.52%) original articles, 2,449 (8.8%) reviews, 69 (0.25%) systematic reviews with meta-analysis, and 171 (0.61%) guidelines. The remaining 6,901 (24.81%) positions were letters to the editors, commentaries, errata, or unclassified. In a per-month analysis we found that in January, two articles (0.007%) on COVID-19 were indexed, 37 (0.13%) in February, 620 (2.23%) in March, 2,514 (9.04%) in April, 5,527 (19.87%) in May, and 18,596 (66.85%) in June. From those articles, we retrieved n = 519 preprint publications (n = 319 from medRxiv and n = 200 from bioRxiv).
We were able to identify 62,051 authors coming from 148 countries. Most authors came from China (n = 11,519), followed by the United States of America (n = 9,666) and Italy (n = 7,261) (Table 1).
Table 1  Top 20 countries with the highest number of publications on COVID-19 between 31 December 2019 and 30 June 2020.
Rank  Country  Number of publications with at least one author from the country  SCImago country rank
1  China  11,519  2
2  United States of America  9,666  1
3  Italy  7,261  6
4  United Kingdom  4,362  3
5  France  3,459  9
6  India  2,568  10
7  Spain  1,765  11
8  Canada  1,679  7
9  Germany  1,596  4
10  Iran  1,349  17
11  Australia  1,317  8
12  Singapore  1,307  34
13  Brazil  1,026  14
14  Turkey  924  16
15  Switzerland  796  15
16  Netherlands  753  12
17  Japan  717  5
18  Taiwan  643  23
19  Belgium  529  20
20  Israel  459  26 In most cases, the country rank based on the number of publications on COVID-19 was similar to the SCImago country rank (Figure 1).
Figure 1  Comparison of SCImago country rank in category medicine and the rank of the countries with the highest number of articles on COVID-19. The number of articles per one million citizens was positively associated with the Human Development Index, number of cases, and deaths due to COVID-19 per one million inhabitants (all p < 0.001) (Figure 2).
Figure 2  Correlation plots between number of articles one author from a country per at least one million citizens and (A) Human Development Index, (B) total number of COVID-19 cases per one million citizens, and (C) total number of COVID-19 deaths per one million citizens. We identified 3,156 unique journal names to which we could match 2,571 titles (80.4%), including 27,296 unique articles that we were able to retrieve. We found that most of the matched journals belonged to category “Medicine” (n = 5,038), followed by “Infectious Diseases” (n = 2,204) and “Cardiology and Cardiovascular Medicine” (n = 1,170) (Table 2).
Table 2  Top 20 journal categories with the highest number of articles on COVID-19 till 30 June 2020.
Rank   Categories   Number of articles
1   Medicine   5,038 (21.18%)
2   Infectious Diseases   2,204 (9.26%)
3   Cardiology and Cardiovascular Medicine   1,170 (4.92%)
4   Dermatology   708 (2.98%)
5   Public Health, Environmental and Occupational Health   531 (2.23%)
6   Neurology   525 (2.21%)
7   Gastroenterology   514 (2.16%)
8   Anesthesiology and Pain Medicine   511 (2.15%)
9   Biochemistry, Genetics, and Molecular Biology   488 (2.05%)
10   Critical Care and Intensive Care Medicine   472 (1.98%)
11   Internal Medicine   436 (1.83%)
12   Hematology   434 (1.82%)
13   Pediatrics, Perinatology, and Child Health   433 (1.82%)
14   Surgery   425 (1.79%)
15   Multidisciplinary   415 (1.74%)
16   Immunology   396 (1.66%)
17   Health Policy   347 (1.46%)
18   Radiology, Nuclear Medicine, and Imaging   337 (1.42%)
19   Epidemiology   323 (1.36%)
20   Otorhinolaryngology   299 (1.26%)