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Billions of doses of COVID-19 vaccines have been administered globally, dramatically reducing SARS-CoV-2 incidence and severity in some settings. Many studies suggest vaccines provide a high degree of protection against infection and disease, but precise estimates vary and studies differ in design, outcomes measured, dosing regime, location, and circulating virus strains. Here we conduct a systematic review of COVID-19 vaccines through February 2022. We included efficacy data from Phase 3 clinical trials for 15 vaccines undergoing WHO Emergency Use Listing evaluation and real-world effectiveness for 8 vaccines with observational studies meeting inclusion criteria. Vaccine metrics collected include protection against asymptomatic infection, any infection, symptomatic COVID-19, and severe outcomes including hospitalization and death, for partial or complete vaccination, and against variants of concern Alpha, Beta, Gamma, Delta, and Omicron. We additionally review the epidemiological principles behind the design and interpretation of vaccine efficacy and effectiveness studies, including important sources of heterogeneity.

Billions of doses of COVID-19 vaccines have been administered around the world, dramatically reducing SARS-CoV-2 incidence in some settings. Many studies suggest vaccines provide a high degree of protection against infection and disease, but precise estimates vary and studies differ in design, outcomes measured, dosing regime, location, and circulating virus strains. Here we conduct a systematic review of COVID-19 vaccines as of August 2021. We included efficacy data from Phase 3 clinical trials for 13 vaccines within the WHO Emergency Use Listing evaluation process and real-world effectiveness for 5 vaccines with observational studies meeting inclusion criteria. Vaccine metrics collected include effects against asymptomatic infection, any infection, symptomatic COVID-19, and severe outcomes including hospitalization and death, for both partial and complete vaccination, and against SARS-CoV-2 variants of concern. In addition, we review the epidemiological principles behind the design and interpretation of vaccine effects, and explain important sources of heterogeneity between studies.

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Background School closures and family economic instability caused by the COVID-19 lockdown measures have threatened the mental health and academic progress of adolescents. Through secondary data analysis of World Vision Asia Pacific Region’s COVID-19 response-assessments in May–June 2020, this study examined whether adolescents’ study, physical, and leisure activities, psychosocial status, and sources of COVID-19 information differed by gender. Methods The assessments used cross-sectional surveys of adolescents in poor communities served by World Vision (n = 5552 males and n = 6680 females) aged 10–18 years old in six countries. The study households of adolescents were selected either by random sampling or non-probability convenience sampling and assessed using telephone or in-person interviews. Multivariate logistic regression analyses examined the relationship between gender and psychosocial status; daily activities (e.g., play, study); and sources of information about COVID-19. Results Participation in remote education was low (range: 0.5–20.7% across countries), with gender difference found only in Vietnam. Compared to males, female adolescents were less likely to play physically with a range of AOR: 0.36–0.55 (n = 5 countries) or play video games with a range of AOR: 0.55–0.72 (n = 2 countries). Female adolescents were more likely to feel isolated or stressed (India, AOR = 1.13, 95%CI:1.00, 1.26); feel unsafe (the Philippines, AOR = 2.22, 95%CI:1.14, 4.33; Vietnam, AOR = 1.31, 95%CI:1.03, 1.47); be concerned about education (India, AOR = 1.24, 95%CI:1.09, 1.41; Myanmar, AOR = 1.59, 95%CI:1.05, 2.40); or be concerned about household income (India, AOR = 1.13, 95%CI:1.00, 1.28; Vietnam, AOR = 1.31, 95%CI:1.09, 1.58). Female adolescents were also less likely to obtain COVID-19 related information through internet/social media (Bangladesh, AOR = 0.51, 95%CI:0.41, 0.64; India, AOR = 0.84, 95%CI:0.73, 0.96; and Myanmar, AOR = 0.65, 95%CI:0.43, 0.97) and mobile call or short message (India, AOR = 0.88, 95%CI:0.80, 0.98) but more likely to get the information from friends (Vietnam, AOR = 1.18, 95%CI:1.02, 1.36) and family (Bangladesh, AOR = 1.44, 95% CI:1.21, 1.70; India, AOR = 1.29, 95% CI:1.15, 1.45). Conclusions An understanding of gender differences in the impacts of COVID-19 on adolescents' schooling, physical, and mental health can inform adolescent protection interventions. Psychosocial support during response and recovery phases needs to pay special attention to gender differences, since female adolescents’ psychosocial status is at higher risk when facing the challenges of this pandemic.