Overall IMD incidence

Overall IMD incidence (per 100 000) was available for 10 non-European countries and 31 European countries (30 countries included within ECDC data and Ukraine national data; Table 1). IMD incidence was generally low across all regions during 2010‒2019 and ranged from 0.0 to 10.2 [Reference Diallo14–25]; the highest incidences were reported for Niger (7.71 in 2015) and Burkina Faso (10.2 in 2012) [Reference Diallo14, Reference Sidikou15]. Excluding these countries, the consistently highest incidence was observed in New Zealand, reaching 2.8 in 2019 [22]. The consistently lowest incidences (<0.2) were observed in Saudi Arabia, the United States and Bulgaria [18, 19, 21]. Some countries, including Niger and Burkina Faso, had defined peaks associated with outbreaks [Reference Diallo14, Reference Sidikou15].

Table 1. Incidence of IMD worldwide from 2010 to 2019 (All ages; all serogroups: per 100 000 individuals; countries with available data)

IMD, invasive meningococcal disease.

A dash indicates no incidence data were available.

Varying trends in incidence were observed during 2010‒2018 [Reference Diallo14–25]. Decreasing trends in incidence were observed in the United States, South Africa and Brazil [16, 21, 23]. Overall IMD incidence in Europe decreased slightly from 0.74 in 2010 to 0.62 in 2018 [19]. In line with this trend, decreasing incidence was observed in Denmark, Finland, Austria and the United Kingdom; however, increasing incidence was observed in Belgium and the Netherlands [19]. Some European countries, such as Spain, showed an initial decline followed by a more recent increase [19]. Globally, trends in incidence also fluctuated in Chile, New Zealand and Russia [17, 22, 24].

IMD incidence by age group

In countries and regions with available data, IMD occurred across all reported age groups (Supplementary Tables S1 and S2) [19–23]. The highest incidences were observed in infants (age <1 year), with rates often approximately 2- to 5-fold in this age group compared with young children (age 1‒4 years) and 10-fold compared with older age groups [19–23]. Particularly high incidence rates in infants during 2010‒2018 were observed in countries including New Zealand, where rates ranged from 10.2 to 47.7 per 100 000 and Ireland, which had rates of 19.3 to 38.8 (Supplementary Tables S1 and S2) [19, 22].

The second-highest incidences occurred among young children (age 1‒4 years) [19–23]. Lithuania had among the highest incidence rates in this age group, ranging from 6.8 to 18.2 during 2010‒2018 (Supplementary Table S2) [19].

A secondary peak in incidence among adolescents/young adults was observed in the United States, where annual IMD incidence was 0.1‒0.21 among those 16‒23 years of age vs. ≤0.1 among those 11‒15 or 24‒44 years of age in 2015‒2018 [21]. Similar secondary peaks in this age group were also observed in Canada, New Zealand and Europe overall but not Brazil (Supplementary Tables S1 and S2) [19, 20, 22, 23]. Secondary peaks in this age group varied by country and year within Europe; for example, the 15‒24-year age group in Sweden had consistently higher IMD incidence (0.58‒1.69) than those 5‒14 (0‒0.59) or 25‒49 (0.12‒0.39) years of age throughout 2010‒2018, whereas incidence among those 15‒24 years of age in Italy (0.30‒0.54) was similar to or lower than for those 5‒14 years of age (0.36‒0.54) during 2010‒2014 [19].

Increased incidence in older adults was observed in the United States (0.13‒0.15 among those ≥65 years of age during 2015‒2018), Canada (0.22‒0.41 among those ≥60 years of age during 2013‒2017) and New Zealand (1.3‒2.3 among those ≥70 years of age during 2015‒2018) but not Brazil (Supplementary Tables S1 and S2) [20–23]. In Europe, incidence among adults ≥50 years of age (0.30‒0.49) was higher than among adults 25‒49 years of age (0.19‒0.26) throughout 2010‒2018, with incidence particularly elevated among those ≥65 years of age (0.33‒0.63) [19]. This trend was echoed in many individual countries such as the United Kingdom, while other countries, such as the Czech Republic, did not exhibit this pattern (Supplementary Table S2) [19].

Overall serogroup distribution of IMD

Serogroup distribution data were available for Quebec (Canada), the United States, Argentina, Brazil, Chile, Colombia, Venezuela, Dominican Republic, Uruguay, Paraguay, African meningitis belt countries (listed in the Supplementary Material), Mozambique, South Africa, Israel, Kuwait, Belarus, Russia, China, Japan, South Korea, Australia, New Zealand and ECDC countries (Figs 2 and 3 and Supplementary Fig. S1) [16, 17, 19, 21–24, 26–37]. Globally, serogroups A, B, C, W and Y caused the majority of IMD, although the serogroup distribution varied across geographical regions at any given time and within the same geographical region over time.

Fig. 2. Percentage serogroup distribution of IMD cases worldwide from 2017 to 2019 (geographical regions with available data) [16, 17, 19, 21–24, 26, 27, 31–33]. Data from China, Colombia, Dominican Republic, Japan, Kuwait, Mozambique, Paraguay, South Korea, Uruguay and Venezuela are not shown. Percentages may not sum to 100% due to rounding. *Serogroup A is included in the “Other” category. ^†Serogroups other than B, C, W and Y are included in the NG category. ^‡Among the African meningitis belt countries (listed in the Supplementary Material), Benin, Burkina Faso, Cameroon, Central African Republic, Ghana, Mali, Niger, Nigeria, Senegal, South Sudan, Chad and Togo contributed serogroup data for 2019. IMD, invasive meningococcal disease; NG, nongroupable.

Fig. 3. Percentage serogroup distribution of IMD cases in selected European countries in 2018 [19]. Percentages may not sum to 100% due to rounding. All serogroup A percentages are directly labelled. IMD, invasive meningococcal disease; NG, nongroupable.

Serogroup A was primarily observed in Burkina Faso, Chad, Niger and Russia (Supplementary Fig. S1a) but was not observed in Burkina Faso, Chad or Niger in recent years likely due to mass vaccination against serogroup A disease in this region [17, 33, Reference LaForce38]. Interestingly, serogroup A accounted for 10% of groupable IMD cases in China during 2015‒2017 and 14%‒25% of groupable IMD cases in Russia during 2016‒2018; however, 34%‒37% of cases in Russia had undetermined serogroups [17, Reference Li28]. Low serogroup A case numbers continue to occur in other countries, including 0.4%‒0.6% of cases in Germany, Italy and Spain in 2018 (Fig. 3) [19].

Serogroup B was the predominant disease-causing serogroup during the observation period in Europe, Israel, South Korea, Australia, New Zealand and Quebec (Supplementary Fig. S1a) [19, 22, 26, 27, Reference Lee30, 31]. Although serogroup B predominated across Europe, serogroup B cases declined over time in many countries including the United Kingdom, France and Germany (Supplementary Fig. S1b) [19]. In other European countries including Poland and Italy, case numbers appeared stable during 2010‒2018 [19]. Serogroup B also predominated in South Africa, Russia and China in recent years (Supplementary Fig. S1a) [16, 17, Reference Li28]. Most recently (2017‒2019), serogroup B accounted for the highest percentage of IMD cases in almost all countries globally (Figs 2 and 3) [16, 17, 19, 21–24, 26, 27, 31–33]. Among the exceptions, serogroup B generally still caused a substantial proportion of IMD; these countries included Brazil (2018, 15%), Sweden (2018, 10%), Norway (2018, 35%), the Netherlands (2018, 36%) and the Czech Republic (2018, 43%) [19, 23]. Unlike other global regions, serogroup B was not responsible for any IMD in African meningitis belt countries in 2019 [33]. As noted, 37% of 2018 cases in Russia had unidentified serogroups; among those remaining, serogroup B constituted the largest percentage (27% of cases) [17].

During the observation period, serogroup C accounted for 66%, 41% and 55% of groupable IMD cases in Brazil, Colombia and Venezuela, respectively [32, 39]. Serogroup C was the second-highest disease-causing serogroup in African meningitis belt countries during 2010‒2019, accounting for 32% of cases [33, 37]. The presence of serogroup C in this region was generally transient; for example, a sharp increase in serogroup C cases was observed in Niger in 2015 due to an epidemic (Supplementary Fig. S1a) [Reference LaForce38]. In Europe, serogroup C varied by country, with an overall increasing trend in the percentage of cases in the Czech Republic, Ireland, Italy and the United Kingdom and an overall decreasing trend in Austria, Belgium, Denmark, Germany, Norway, Poland and Sweden; no major trends were observed in other European countries (Supplementary Fig. S1b) [19]. An increase in the percentage of IMD due to serogroup C was observed in the United States, from 15% in 2015 to 27% in 2018; however, serogroup C case numbers increased from 54 in 2015 to 99 in 2016 and then decreased slightly to 90 cases in 2018 (Supplementary Fig. S1a) [21]. The most recent data (2017‒2019) show that serogroup C was present, albeit in varying percentages, across every global region (other than Israel in 2018, although Israel did record serogroup C cases in the preceding years; Figs 2 and 3, Supplementary Fig. S1) [16, 17, 19, 21–24, 26,27, 31–33]. Specifically, serogroup C accounted for 27% of cases in each of Brazil and the United States and a substantial percentage of IMD in eastern European countries (Poland, 22%; Czech Republic, 44%; Hungary, 34%; Slovakia, 17%) in 2018 [19, 21, 23].

Serogroup W was the predominant disease-causing serogroup in the African meningitis belt during 2010‒2019 (43% of IMD cases) [33, 37] and in Chile during 2012‒2018 (50%–73% of cases; Supplementary Fig. S1a) [24]. Outbreaks of serogroup W were observed in the African meningitis belt, with sharp increases in case numbers in Burkina Faso in 2012, Togo in 2016 and Chad in 2019 [33, 37]. Over the first half of the decade (2010‒2014), serogroup W predominated in Argentina (48%‒56% of cases) and South Africa (39%‒51% of serogrouped cases) [16, 32]. Over the second half of the decade, the percentage of serogroup W cases decreased over time in Argentina and South Africa, where serogroup B case numbers were stable or decreased but constituted an increasing percentage of IMD due to overall decreases in IMD, whereas increasing trends in the percentage of serogroup W cases were observed in Chad, Europe, Israel, Australia, New Zealand and Russia [16, 17, 19, 22, 27, 31–33, 37]. Since 2016, serogroup W case numbers have risen in Australia [31]. In New Zealand, increasing serogroup W case numbers led to serogroup W replacing serogroup C as the second-highest disease-causing serogroup, reaching 27% of IMD cases in 2019 [22]. Most recently (2017‒2019), the percentage of IMD cases due to serogroup W across countries in the southern hemisphere was generally substantial, ranging from 19% (South Africa, 2018) to 44% (Chile, 2019), with the exception of Brazil, where serogroup W did not expand to the same extent (2019, 4%; Fig. 2) [16, 22–24, 31, 32]. Similarly, 2018 data showed that serogroup W accounted for 3% (Greece) to 50% (the Netherlands) of cases across European countries, indicating varied expansion of serogroup W across the continent (Fig. 3) [19].

Serogroup Y, although not a predominant contributor to IMD globally, showed an increasing trend in case numbers from 2010 to 2018 in Europe, Israel, Australia and New Zealand (Supplementary Fig. S1a) [19, 22, 27, 31]. During 2013‒2014, serogroup Y accounted for 42% of IMD cases in Japan [Reference Fukusumi29]. In other countries, serogroup Y comprised a stable proportion of cases during the observation period; this occurred both in countries with substantial presence of serogroup Y (e.g. the United States), and those where serogroup Y caused a relatively low percentage of IMD (e.g. Argentina; Supplementary Table S3) [21, 32]. Of note, in 2018, the percentage of IMD due to serogroup Y in northern European countries ranged from 29% in Sweden to 46% in Norway, where it was predominant (Fig. 3) [19].

Other serogroups, including X, Z and E, were minor contributors to IMD worldwide [16, 17, 19, 21–24, 26, 27, Reference Lee30–33, 37]. Serogroup X cases were mostly limited to African meningitis belt countries, with the exception of sporadic cases.

IMD serogroup distribution by age group

Data on IMD serogroup distribution by age group were available from Argentina, Brazil, Chile, the United States, Australia, New Zealand and Europe [19, 21, 22, 24, 31, 32, 39]. Serogroups B, C, W and Y occurred across all age groups; however, trends were observed with respect to the predominant serogroup within age groups.

Serogroup B predominated across many age groups and regions during the study period [19, 21, 22, 24, 31, 32, 39]. Among infants and young children, serogroup B caused 40%‒100% of cases in Australia during 2010‒2018 and 41%‒80% of cases in the United States during 2015‒2018 (Supplementary Table S3) [21, 31]. In some countries, the percentage of cases caused by serogroup B was similarly high among adolescents/young adults as infants; this occurred in the United States (during 2015‒2018) and New Zealand (2018‒2019; Supplementary Table S3) [21, 22]. However, the dominance of serogroup B was frequently much more pronounced among younger compared with older age groups, with the relatively higher percentage of serogroup B disease in younger age groups persisting even in the context of broader decreases in serogroup B disease. For example, in Europe, serogroup B caused 75%‒84% of cases among age groups comprising infants and young children but 58%‒63% and 41%‒51% of cases among individuals 15‒24 and ≥50 years of age, respectively, during 2010‒2013, while percentages during 2016‒2018 were 63%‒70%, 48%‒50% and 29%‒30%, respectively [19]. Similarly, in Australia, percentages decreased from 86%‒100% and 44%‒88% among age groups comprising individuals ≤4 and ≥45 years of age, respectively, during 2010‒2012 to 40%‒62% and 10%‒37% during 2016‒2018 [31].

Serogroup C trends varied across age groups in Brazil, causing a stable majority (usually 50%‒80%) of IMD among those 15‒29 and ≥60 years of age during 2011‒2018 and decreasing percentages among infants and children 2‒4 years of age (Supplementary Table S3) [32, 39]. In other regions, serogroup C occurred in generally lower percentages across all age groups but was sometimes more frequent in adolescent/young adult and older age groups. For example, serogroup C caused 6%‒12% of IMD in Europe among those <1 and 1‒4 years of age during the study period, but 12%‒19% of cases among those 15‒24 and ≥50 years of age [19].

The expansion of serogroup W disease was evident in many age groups across countries (Supplementary Table S3) [19, 21, 22, 24, 31, 32, 39]. For example, serogroup W comprised ≤7% of cases across age groups in Australia in 2012 but rose to 17%‒50% by 2018 [31]. In many countries, percentages of cases caused by serogroup W rose more steeply in older adults compared with other age groups; this was the case for Europe overall as well as individual European countries including the Netherlands and the United Kingdom [19]. In the United States, serogroup W disease was generally more frequent among adults ≥45 years of age compared with younger age groups, although percentages in older age groups decreased during 2015‒2018 [21]. Unlike many other countries, decreasing trends in serogroup W case numbers were observed in Argentina and Chile among older adults and most other age groups during the study period [24, 32].

Across countries, serogroup Y often caused a higher percentage of IMD among older adults compared with other age groups (Supplementary Table S3) [19, 21, 22, 24, 31, 32]. This was true in New Zealand (during 2018‒2019) [22] and the United States (during 2015‒2018) [21], among other countries (Supplementary Table S3). Similarly, serogroup Y cases in Europe were much more frequent in adults ≥50 years of age (2010‒2018) followed by adolescents/young adults compared with younger age groups, with this trend holding true for many individual countries (Supplementary Table S3) [19].