Key Points Question What is the percentage of asymptomatic individuals with positive test results for SARS-CoV-2 among tested individuals and those with confirmed COVID-19 diagnosis? Findings In this systematic review and meta-analysis of 95 unique studies with 29 776 306 individuals undergoing testing, the pooled percentage of asymptomatic infections was 0.25% among the tested population and 40.50% among the population with confirmed COVID-19. Meaning The high percentage of asymptomatic infections from this study highlights the potential transmission risk of asymptomatic infections in communities.

IMPORTANCESeveral studies were conducted to estimate the average incubation period of COVID-19; however, the incubation period of COVID-19 caused by different SARS-CoV-2 variants is not well described. OBJECTIVE To systematically assess the incubation period of COVID-19 and the incubation periods of COVID-19 caused by different SARS-CoV-2 variants in published studies.

Background: Asymptomatic infections are potential sources of transmission for coronavirus disease 2019, especially during the epidemic of the SARS-CoV-2 Omicron variant. We aimed to assess the percentage of asymptomatic infections among SARS-CoV-2 Omicron variant-positive individuals detected by gene sequencing or specific polymerase chain reaction (PCR). Methods: We searched PubMed, EMBASE, and Web of Science from 26 November 2021 to 13 April 2022. This meta-analysis was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines and was registered with PROSPERO (CRD42022327894). Three researchers independently extracted data and two researchers assessed quality using pre-specified criteria. The pooled percentage with 95% confidence interval (CI) of asymptomatic infections of SARS-CoV-2 Omicron was estimated using random-effects models. Results: Our meta-analysis included eight eligible studies, covering 7640 Omicron variant-positive individuals with 2190 asymptomatic infections. The pooled percentage of asymptomatic infections was 32.40% (95% CI: 25.30–39.51%) among SARS-CoV-2 Omicron variant-positive individuals, which was higher in the population in developing countries (38.93%; 95% CI: 19.75–58.11%), with vaccine coverage ≥ 80% (35.93%; 95% CI: 25.36–46.51%), with a travel history (40.05%; 95% CI: 7.59–72.51%), community infection (37.97%; 95% CI: 10.07–65.87%), and with a median age < 20 years (43.75%; 95% CI: 38.45–49.05%). Conclusion: In this systematic review and meta-analysis, the pooled percentage of asymptomatic infections was 32.40% among SARS-CoV-2 Omicron variant-positive individuals. The people who were vaccinated, young (median age < 20 years), had a travel history, and were infected outside of a clinical setting (community infection) had higher percentages of asymptomatic infections. Screening is required to prevent clustered epidemics or sustained community transmission caused by asymptomatic infections of Omicron variants, especially for countries and regions that have successfully controlled SARS-CoV-2.

Background Malaria is a life-threatening disease worldwide, but lacks studies on its incidence at the global level. We aimed to describe global trends and regional diversities in incidence of malaria infection, to make global tailored implications for malaria prevention. Methods We used the data from the Global Burden of Disease Study 2019. The age-standardized incidence rate (ASR) and absolute number of malaria episodes showed the epidemic status of malaria infection. The estimated annual percentage change (EAPC) of ASR and changes in malaria episodes quantified the malaria incidence trends. The connection between ASRs and traveler number indicated infection risk for travelers. Results Globally, the malaria ASR decreased by an average 0.80% (95%CI 0.58%–1.02%) per year from 1990 to 2019; however, it slightly increased from 3195.32 per 100 000 in 2015 to 3247.02 per 100 000 in 2019. The incidence rate of children under 5 was higher than other age groups. 40 countries had higher ASRs in 2019 than in 2015, with the largest expansion in Cabo Verde (from 2.02 per 100 000 to 597.00 per 100 000). After 2015, the ASRs in high-middle, middle and low-middle SDI (the Socio-demographic Index) regions began to rise, and the uptrends remained in 2019. Central, Western and Eastern Sub-Saharan Africa had the highest ASRs since 1990, and traveler number in Eastern and Western sub-Saharan Africa increased by 31.24% and 7.58%, respectively from 2017 to 2018. Especially, most countries with ASR over 10 000 per 100 000 had increase in traveler number from 2017 to 2018, with the highest change by 89.56% in Mozambique. Conclusions Malaria is still a public health threat for locals and travelers in sub-Sharan Africa and other malaria-endemic areas, especially for children under 5. There were unexpected global uptrends of malaria ASRs from 2015 to 2019. More studies are needed to achieve the goal of malaria elimination.

Background and Objective: Lower respiratory infections (LRIs) are a leading cause of death worldwide. We aimed to estimate the trends of global and regional aetiologies, risk factors and mortality of LRIs from 1990 to 2019. Methods: From the Global Burden of Disease (GBD) Study 2019, we collected relevant data, including annual LRI deaths, mortality and deaths and mortality attributable to the four high-burden aetiologies and 14 risk factors during 1990-2019. To quantify the temporal trends, estimated annual percentage changes (EAPCs) were calculated by fitting linear regression model. Results: Globally, the age-standardized mortality due to LRIs decreased by an average of 2.39% (95% CI 2.33%-2.45%) per year, from 66.67 deaths per 100,000 in 1990 to 35.72 deaths per 100,000 in 2019. Low Socio-demographic Index regions, South Asia and Sub-Saharan Africa had the heaviest burden of LRIs. The age-standardized mortality decreased in 18 GBD regions, whereas increased in Southern Latin America (EAPC = 1.20, 95% CI 1.03-1.37). LRIs led to considerable deaths among children under 5 years and adults older than 70 years. Streptococcus pneumoniae was the first leading aetiology, accounting for over 50% of LRI deaths. Household air pollution from solid fuels, child wasting and ambient particulate matter pollution were the three leading risk factors for LRI mortality in 2019. Conclusion: LRIs remain an important health problem globally, especially in some vulnerable areas and among children under 5 and adults over 70 years. Future researches focusing on the aetiologies and risk factors for LRIs are needed to provide targeted and updated prevention strategies. K E Y W O R D S lower respiratory infections, mortality, prevention, trend Liangyu Kang and Wenzhan Jing contributed equally to this study.