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Knowing whether COVID-19 vaccine effectiveness wanes is crucial for informing vaccine policy, such as the need for and timing of booster doses. We aimed to systematically review the evidence for the duration of protection of COVID-19 vaccines against various clinical outcomes, and to assess changes in the rates of breakthrough infection caused by the delta variant with increasing time since vaccination. This study was designed as a systematic review and meta-regression. We did a systematic review of preprint and peer-reviewed published article databases from June 17, 2021, to Dec 2, 2021. Randomised controlled trials of COVID-19 vaccine efficacy and observational studies of COVID-19 vaccine effectiveness were eligible. Studies with vaccine efficacy or effectiveness estimates at discrete time intervals of people who had received full vaccination and that met predefined screening criteria underwent full-text review. We used random-effects meta-regression to estimate the average change in vaccine efficacy or effectiveness 1–6 months after full vaccination. Of 13 744 studies screened, 310 underwent full-text review, and 18 studies were included (all studies were carried out before the omicron variant began to circulate widely). Risk of bias, established using the risk of bias 2 tool for randomised controlled trials or the risk of bias in non-randomised studies of interventions tool was low for three studies, moderate for eight studies, and serious for seven studies. We included 78 vaccine-specific vaccine efficacy or effectiveness evaluations (Pfizer–BioNTech-Comirnaty, n=38; Moderna-mRNA-1273, n=23; Janssen-Ad26.COV2.S, n=9; and AstraZeneca-Vaxzevria, n=8). On average, vaccine efficacy or effectiveness against SARS-CoV-2 infection decreased from 1 month to 6 months after full vaccination by 21·0 percentage points (95% CI 13·9–29·8) among people of all ages and 20·7 percentage points (10·2–36·6) among older people (as defined by each study, who were at least 50 years old). For symptomatic COVID-19 disease, vaccine efficacy or effectiveness decreased by 24·9 percentage points (95% CI 13·4–41·6) in people of all ages and 32·0 percentage points (11·0–69·0) in older people. For severe COVID-19 disease, vaccine efficacy or effectiveness decreased by 10·0 percentage points (95% CI 6·1–15·4) in people of all ages and 9·5 percentage points (5·7–14·6) in older people. Most (81%) vaccine efficacy or effectiveness estimates against severe disease remained greater than 70% over time. COVID-19 vaccine efficacy or effectiveness against severe disease remained high, although it did decrease somewhat by 6 months after full vaccination. By contrast, vaccine efficacy or effectiveness against infection and symptomatic disease decreased approximately 20–30 percentage points by 6 months. The decrease in vaccine efficacy or effectiveness is likely caused by, at least in part, waning immunity, although an effect of bias cannot be ruled out. Evaluating vaccine efficacy or effectiveness beyond 6 months will be crucial for updating COVID-19 vaccine policy. Coalition for Epidemic Preparedness Innovations.

The global surge in the omicron (B.1.1.529) variant has resulted in many individuals with hybrid immunity (immunity developed through a combination of SARS-CoV-2 infection and vaccination). We aimed to systematically review the magnitude and duration of the protective effectiveness of previous SARS-CoV-2 infection and hybrid immunity against infection and severe disease caused by the omicron variant. For this systematic review and meta-regression, we searched for cohort, cross-sectional, and case–control studies in MEDLINE, Embase, Web of Science, ClinicalTrials.gov, the Cochrane Central Register of Controlled Trials, the WHO COVID-19 database, and Europe PubMed Central from Jan 1, 2020, to June 1, 2022, using keywords related to SARS-CoV-2, reinfection, protective effectiveness, previous infection, presence of antibodies, and hybrid immunity. The main outcomes were the protective effectiveness against reinfection and against hospital admission or severe disease of hybrid immunity, hybrid immunity relative to previous infection alone, hybrid immunity relative to previous vaccination alone, and hybrid immunity relative to hybrid immunity with fewer vaccine doses. Risk of bias was assessed with the Risk of Bias In Non-Randomized Studies of Interventions Tool. We used log-odds random-effects meta-regression to estimate the magnitude of protection at 1-month intervals. This study was registered with PROSPERO (CRD42022318605). 11 studies reporting the protective effectiveness of previous SARS-CoV-2 infection and 15 studies reporting the protective effectiveness of hybrid immunity were included. For previous infection, there were 97 estimates (27 with a moderate risk of bias and 70 with a serious risk of bias). The effectiveness of previous infection against hospital admission or severe disease was 74·6% (95% CI 63·1–83·5) at 12 months. The effectiveness of previous infection against reinfection waned to 24·7% (95% CI 16·4–35·5) at 12 months. For hybrid immunity, there were 153 estimates (78 with a moderate risk of bias and 75 with a serious risk of bias). The effectiveness of hybrid immunity against hospital admission or severe disease was 97·4% (95% CI 91·4–99·2) at 12 months with primary series vaccination and 95·3% (81·9–98·9) at 6 months with the first booster vaccination after the most recent infection or vaccination. Against reinfection, the effectiveness of hybrid immunity following primary series vaccination waned to 41·8% (95% CI 31·5–52·8) at 12 months, while the effectiveness of hybrid immunity following first booster vaccination waned to 46·5% (36·0–57·3) at 6 months. All estimates of protection waned within months against reinfection but remained high and sustained for hospital admission or severe disease. Individuals with hybrid immunity had the highest magnitude and durability of protection, and as a result might be able to extend the period before booster vaccinations are needed compared to individuals who have never been infected. WHO COVID-19 Solidarity Response Fund and the Coalition for Epidemic Preparedness Innovations.

Phase 3 randomized-controlled trials have provided promising results of COVID-19 vaccine efficacy, ranging from 50 to 95% against symptomatic disease as the primary endpoints, resulting in emergency use authorization/listing for several vaccines. However, given the short duration of follow-up during the clinical trials, strict eligibility criteria, emerging variants of concern, and the changing epidemiology of the pandemic, many questions still remain unanswered regarding vaccine performance. Post-introduction vaccine effectiveness evaluations can help us to understand the vaccine's effect on reducing infection and disease when used in real-world conditions. They can also address important questions that were either not studied or were incompletely studied in the trials and that will inform evolving vaccine policy, including assessment of the duration of effectiveness; effectiveness in key subpopulations, such as the very old or immunocompromised; against severe disease and death due to COVID-19; against emerging SARS-CoV-2 variants of concern; and with different vaccination schedules, such as number of doses and varying dosing intervals. WHO convened an expert panel to develop interim best practice guidance for COVID-19 vaccine effectiveness evaluations. We present a summary of the interim guidance, including discussion of different study designs, priority outcomes to evaluate, potential biases, existing surveillance platforms that can be used, and recommendations for reporting results.

The global response to COVID-19 saw the most rapid and extensive vaccination rollout in history. Yet there were large disparities in the introduction, scale-up, and evaluation of programmes. To systematically quantify these disparities, we generate linkages across public datasets containing country- and territory-level income data, COVID-19 vaccination rates, and COVID-19 vaccine effectiveness (VE). Our results show that, compared with high-income countries, lower-income countries introduced vaccines later, were less likely to achieve key coverage milestones, and were slower to do so where these milestones were achieved. The literature on primary series COVID-19 VE has been dominated by studies of mRNA vaccines from high-income countries, with data for other vaccines and lower-income countries appearing later and in substantially lower quantities. For vaccines with available VE data across multiple income settings (BNT162b2, mRNA-1273, and ChAdOx1-S), our meta-regression highlights robust protection against severe COVID-19, with no significant differences in primary series VE according to country-level income status during the Delta and Omicron periods. Our findings demonstrate the strong protection conferred by COVID-19 vaccines across diverse populations. Nonetheless, our results quantify the stark disparities that pervaded each stage of COVID-19 vaccine implementation, and highlight evidence gaps related to products and platforms being used across much of the globe. The COVID-19 vaccine rollout saw large global disparities in the introduction, scale-up, and evaluation of immunisation programmes. Here, the authors systematically quantify these disparities through linkage of public data sources.

Globally, more than 5 million people have died from Covid-19 since the start of the pandemic. 1 This is certainly a grim number, but we are starting to see the lifesaving effect of vaccines. 2 From the global public health perspective, the initial primary objective of Covid-19 vaccination is to decrease the severe consequences of Covid-19, allowing for the earliest possible stabilization of health care systems, communities, and economies. The vaccines studied to date are highly effective against severe disease and death. 3 Although vaccine effectiveness against infection appears to decline with increasing time since vaccination, it is reassuring that vaccines continue to . . .

In 2010, the World Health Assembly (WHA) set the following three milestones for measles control to be achieved by 2015: 1) increase routine coverage with the first dose of measles-containing vaccine (MCV1) among children aged 1 year to ≥90% at the national level and to ≥80% in every district, 2) reduce global annual measles incidence to <5 cases per 1 million population, and 3) reduce global measles mortality by 95% from the 2000 estimate* (1). In 2012, WHA endorsed the Global Vaccine Action Plan,† with the objective of eliminating measles§ in five of the six World Health Organization (WHO) regions by 2020. This report describes progress toward WHA milestones and regional measles elimination during 2000-2019 and updates a previous report (2). During 2000-2010, estimated MCV1 coverage increased globally from 72% to 84% but has since plateaued at 84%-85%. All countries conducted measles surveillance; however, approximately half did not achieve the sensitivity indicator target of two or more discarded measles and rubella cases per 100,000 population. Annual reported measles incidence decreased 88%, from 145 to 18 cases per 1 million population during 2000-2016; the lowest incidence occurred in 2016, but by 2019 incidence had risen to 120 cases per 1 million population. During 2000-2019, the annual number of estimated measles deaths decreased 62%, from 539,000 to 207,500; an estimated 25.5 million measles deaths were averted. To drive progress toward the regional measles elimination targets, additional strategies are needed to help countries reach all children with 2 doses of measles-containing vaccine, identify and close immunity gaps, and improve surveillance.In 2010, the World Health Assembly (WHA) set the following three milestones for measles control to be achieved by 2015: 1) increase routine coverage with the first dose of measles-containing vaccine (MCV1) among children aged 1 year to ≥90% at the national level and to ≥80% in every district, 2) reduce global annual measles incidence to <5 cases per 1 million population, and 3) reduce global measles mortality by 95% from the 2000 estimate* (1). In 2012, WHA endorsed the Global Vaccine Action Plan,† with the objective of eliminating measles§ in five of the six World Health Organization (WHO) regions by 2020. This report describes progress toward WHA milestones and regional measles elimination during 2000-2019 and updates a previous report (2). During 2000-2010, estimated MCV1 coverage increased globally from 72% to 84% but has since plateaued at 84%-85%. All countries conducted measles surveillance; however, approximately half did not achieve the sensitivity indicator target of two or more discarded measles and rubella cases per 100,000 population. Annual reported measles incidence decreased 88%, from 145 to 18 cases per 1 million population during 2000-2016; the lowest incidence occurred in 2016, but by 2019 incidence had risen to 120 cases per 1 million population. During 2000-2019, the annual number of estimated measles deaths decreased 62%, from 539,000 to 207,500; an estimated 25.5 million measles deaths were averted. To drive progress toward the regional measles elimination targets, additional strategies are needed to help countries reach all children with 2 doses of measles-containing vaccine, identify and close immunity gaps, and improve surveillance.

Abstract Background Surveillance data from a large measles outbreak in Mongolia suggested increased case fatality ratio (CFR) in the second of 2 waves. To confirm the increase in CFR and identify risk factors for measles death, we enhanced mortality ascertainment and conducted a case-control study among infants hospitalized for measles. Methods We linked national vital records with surveillance data of clinically or laboratory-confirmed infant (aged <12 months) measles cases with rash onset during March–September 2015 (wave 1) and October 2015–June 2016 (wave 2). We abstracted medical charts of 95 fatal cases and 273 nonfatal cases hospitalized for measles, matched by age and sex. We calculated adjusted matched odds ratios (amORs) and 95% confidence intervals (CIs) for risk factors. Results Infant measles deaths increased from 3 among 2224 cases (CFR: 0.13%) in wave 1 to 113 among 4884 cases (CFR: 2.31%) in wave 2 (P < .001). Inpatient admission, 7–21 days before measles rash onset, for pneumonia or influenza (amOR: 4.5; CI, 2.6–8.0), but not other diagnoses, was significantly associated with death. Discussion Measles infection among children hospitalized with respiratory infections likely increased deaths due to measles during wave 2. Preventing measles virus nosocomial transmission likely decreases measles mortality. During a nationwide measles outbreak in Mongolia during 2015‒2016, health care-associated measles virus infection of infants hospitalized for pneumonia or influenza was significantly associated with measles death. Epidemiologic and laboratory evidence suggested influenza and measles coinfection might have increased mortality.

In the pre-vaccination era, the prevalence of chronic hepatitis B virus (HBV) infection in the World Health Organization (WHO) Eastern Mediterranean Region (EMR) ranged from two to seven percent in a total population of over 580 million people. Mortality estimates place cirrhosis among the top ten causes of years of life lost in the EMR. The region has made notable achievements, improving coverage from only 6% in 1992, when WHO recommended hepatitis B vaccination of all infants, to 83% in 2014. Member states adopted a hepatitis B control target in 2009 to reduce chronic hepatitis B virus infection prevalence to less than one percent among children aged <5 years by 2015. This report reviews progress toward achievement, challenges faced, and the next steps forward of hepatitis B control among children in the EMR.

Limitations of our systematic review included potential biases in evaluating duration of vaccine effectiveness as described previously,1 scarce data for non-mRNA vaccines, and short follow-up after booster vaccination. Given the high prevalence of the omicron variant, omicron infection might have been incidental rather than causal among some hospitalised people, which would have resulted in underestimated vaccine effectiveness against severe disease.2 Vaccine effectiveness of primary series COVID-19 vaccines against severe disease when the omicron variant was predominant was lower than that observed pre-omicron but showed little decline after vaccination. MMH reports research grants from WHO, Coalition for Epidemic Preparedness Innovations (CEPI), Asian Development Bank (ADB), Bill & Melinda Gates Foundation, and Pfizer (all paid to the institution).

Hepatitis B vaccine birth dose (HepB-BD) was introduced in Lao People’s Democratic Republic to prevent perinatal hepatitis B virus transmission in 2008; high coverage is challenging since only 38% of births occur in a health facility. Healthcare workers report being unaware of home births and thus unable to conduct timely postnatal care (PNC) home visits. A quasi-experimental pilot study was conducted wherein mobile phones and phone credits were provided to village health volunteers (VHV) and healthcare workers (HCWs) to assess whether this could improve HepB-BD administration, as well as birth notification and increase home visits. From April to September 2014, VHVs and HCWs in four selected intervention districts were trained, supervised, received outreach per diem for conducting home visits, and received mobile phones and phone credits. In three comparison districts, VHVs and HCWs were trained, supervised, and received outreach per diem for conducting home visits. A post-study survey compared HepB-BD coverage among children born during the study and children born one year before. HCWs and VHVs were interviewed about the study. Among intervention districts, 463 study children and 406 pre-study children were enrolled in the survey; in comparison districts, 347 study children and 309 pre-study children were enrolled. In both arms, there was a significant improvement in the proportion of children reportedly receiving a PNC home visit (intervention p<0.0001, comparison p=0.04). The median difference in village level HepB-BD coverage (study cohort minus pre-study cohort), was 57% (interquartile range [IQR] 32–88%, p<0.0001) in intervention districts, compared with 20% (IQR 0–50%, p<0.0001) in comparison districts. The improvement in the intervention districts was greater than in the comparison districts (p=0.0009). Our findings suggest that the provision of phones and phone credits might be one important factor for increasing coverage. However, reasons for improvement in both arms are multifactorial and discussed.