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Before the emergence of the delta variant, it was reported that after at least one dose of the mRNA vaccine by Pfizer or the adenoviral vector vaccine by Astra Zeneca, the risk of symptomatic cases in household contacts of vaccinated cases was about 50% lower than that among household contacts of unvaccinated cases.1 The now globally dominant delta variant is more transmissible2 and associated with reduced vaccine effectiveness, particularly against mild breakthrough infections, whereas protection against severe disease is not greatly reduced.3 Data are lacking on whether the effect of vaccination on transmission is lower for the delta variant and new insights on this are provided by a study done in the UK when the delta variant was the predominant strain, reported in The Lancet Infectious Diseases.4 Anika Singanayagam and colleagues did a carefully designed cohort study whereby 602 community contacts (household and non-household) identified via the UK contact tracing system and 471 COVID-19 index cases were enrolled through the Assessment of Transmission and Contagiousness of COVID-19 in Contacts (ATACCC) study. [...]the authors compared the viral kinetics in breakthrough delta variant infections in vaccinated people with delta variant infections in unvaccinated people. The question of whether booster doses will improve the impact on transmission should be addressed as a top priority.7 Research efforts should be directed towards enhancing existing vaccines or developing new vaccines that also protect against asymptomatic infections and onward transmission. [...]we have such vaccines, public health and social measures will still need to be tailored towards mitigating community and household transmission in order to keep the pandemic at bay.

Group B Streptococcus (GBS) is a leading cause of infant mortality, particularly in low- and middle-income countries (LMICs). Several maternal GBS vaccine candidates, aimed at protecting infants, are progressing through clinical trials. The World Health Organisation (WHO) aims to ensure equitable access to safe, effective, and affordable vaccines of assured quality in LMICs, by facilitating regulatory pathways. An alternate approval pathway, based on safety and an immunological endpoint thought to predict clinical benefit (commonly referred to as serological threshold of risk reduction [SToRR]), is being considered for GBS maternal vaccines. Since this approach is new to many LMICs regulators and policymakers, WHO organized consultative meetings at national, regional, and global levels to discuss the feasibility and potential challenges of approving a GBS vaccine based on safety and immunogenicity data alone. These consultations focused on evidence supporting SToRR, their use as endpoints to infer protection, and post-licensure requirements. The aim of the consultations was to reduce the delay between vaccine development, licensure, policy recommendations and use in high-burden LMICs.

Abstract Rationale The International Health Regulations (IHR) have been the governing framework for global health security since 2007. Declaring public health emergencies of international concern (PHEIC) is a cornerstone of the IHR. Here we review how PHEIC are formally declared, the diseases for which such declarations have been made from 2007 to 2020 and justifications for such declarations. Key findings Six events were declared PHEIC between 2007 and 2020: the 2009 H1N1 influenza pandemic, Ebola (West African outbreak 2013–2015, outbreak in Democratic Republic of Congo 2018–2020), poliomyelitis (2014 to present), Zika (2016) and COVID-19 (2020 to present). Poliomyelitis is the longest PHEIC. Zika was the first PHEIC for an arboviral disease. For several other emerging diseases a PHEIC was not declared despite the fact that the public health impact of the event was considered serious and associated with potential for international spread. Recommendations The binary nature of a PHEIC declaration is often not helpful for events where a tiered or graded approach is needed. The strength of PHEIC declarations is the ability to rapidly mobilize international coordination, streamline funding and accelerate the advancement of the development of vaccines, therapeutics and diagnostics under emergency use authorization. The ultimate purpose of such declaration is to catalyse timely evidence-based action, to limit the public health and societal impacts of emerging and re-emerging disease risks while preventing unwarranted travel and trade restrictions.

Israel delivered more than 10 million doses within 4 months; by April 19, 2021, 54% of the entire population of 9·1 million people, and 88% of people aged 50 years or older, had received two doses.1 Factors contributing to Israel's rapid roll-out include its small geographical and population sizes; advanced information technology that allowed prioritisation, allocation, and documentation of vaccines for eligible individuals; effective cooperation between government and community-based health funds, which were charged with providing vaccines to those they insured; and experience in rapid large-scale emergency responses.2 Vaccines were rolled out around the time of Israel's third and largest wave of SARS-CoV-2 infections, with a peak 7-day moving average of 8328 new infections per day, which resulted in a 2-month national lockdown. [...]Israel's setting provided a robust platform on which to examine vaccine effectiveness and the impact of high vaccine coverage in real-life conditions at a national level. WHO has published a best practice guidance document on how to conduct vaccine effectiveness assessments using observational study designs.12 Israel's experience provides impetus for countries to proactively pursue high vaccine coverage to protect the population;8 however, rollout would need to follow the WHO prioritisation roadmap to maximise the public health impact, in light of vaccine supply constraints. Timely reporting of vaccine effectiveness against variants of concern, the duration of protection across age groups and geographical settings, and the effectiveness of alternative dosing regimens is crucial to provide data-driven immunisation policies.12 Amir Levy/Stringer/Getty Images EL reports personal fees from Sanofi Pasteur for participation in a global advisory board of influenza vaccination, outside the area of work commented on here.

Chloroquine has in-vitro activity against influenza and could be an ideal candidate for worldwide prevention of influenza in the period between onset of a pandemic with a virulent influenza strain and the development and widespread dissemination of an effective vaccine. We aimed to assess the efficacy of such an intervention. In this randomised, double-blind, placebo-controlled trial done at a single centre in Singapore, we randomly assigned (1:1) healthy adults to receive chloroquine phosphate (500 mg/day for 1 week, then once a week to complete 12 weeks) or matching placebo by use of a computer-generated randomisation list. Participants filled an online symptom diary every week, supplemented by daily diaries and self-administered nasal swabs when unwell. Haemagglutination-inhibition assays for influenza A (H1N1, H3N2) and B were done on blood samples taken at baseline and after 12 weeks. The primary outcome was laboratory-confirmed clinical influenza defined by specific symptoms accompanied by influenza RNA on nasal swabs or a four-fold increase in haemagglutination-inhibition titres over the 12-week study period. Analysis was by intention to treat. This trial was registered with ClinicalTrials.gov, number NCT01078779. From November, 2009, to February, 2010, we recruited 1516 eligible participants. 1496 (96%) returned at week 12 and were included in the efficacy analysis. Adherence to study intervention was 97%, and 94% of the scheduled weekly diaries were completed. Eight (1%) of 738 participants had laboratory-confirmed clinical influenza in the placebo group and 12 (2%) of 724 in the chloroquine group (relative risk 1·53, 95% CI 0·63–3·72; p=0·376). 29 (4%) of 738 had laboratory-confirmed influenza infection (symptomatic or asymptomatic) in the placebo group and 38 (5%) of 724 in the chloroquine group (1·34, 0·83–2·14; p=0·261). 249 (33%) of 759 participants reported adverse events (mostly mild) in the placebo group and 341 (45%) of 757 in chloroquine group (p<0·0001). Headache, dizziness, nausea, diarrhoea, and blurred vision were more common in the chloroquine group, but rarely resulted in treatment discontinuation. One serious adverse event (hepatitis) was possibly related to chloroquine. Although generally well tolerated by a healthy community population, chloroquine does not prevent infection with influenza. Alternative drugs are needed for large-scale prevention of influenza. National Medical Research Council, Singapore.

Dengue fever, caused by four distinct serotypes of the dengue virus (DENV1-4), poses a public health concern for much of the world. The NIH's Laboratory of Infectious Diseases at the National Institute of Allergy and Infectious Diseases (NIAID) has developed a series of single-dose, live-attenuated tetravalent DENV vaccines, including TV005. However, phase III trials require a lengthy three-to-five year follow-up. In contrast, controlled human infection models (CHIMs) offer a faster means to assess vaccine efficacy for any of the four serotypes. In this issue of the JCI, Pierce, Durbin, and colleagues conducted a CHIM study with attenuated DENV2 and DENV3 challenge viruses in individuals six months after vaccination with TV005. The TV005 vaccine was well tolerated and effectively protected all vaccinated individuals from viremia and rash during challenges with DENV2 or DENV3. Notably, vaccine recipients also showed serotype-specific efficacy. While long-term studies are still needed, these findings represent an important step in providing protection against dengue virus.

Teaser: Our review found the average R0 for 2019-nCoV to be 3.28, which exceeds WHO estimates of 1.4 to 2.5.

We need to rapidly detect and respond to public rumours, perceptions, attitudes and behaviours around COVID-19 and control measures. The creation of an interactive platform and dashboard to provide real-time alerts of rumours and concerns about coronavirus spreading globally would enable public health officials and relevant stakeholders to respond rapidly with a proactive and engaging narrative that can mitigate misinformation.

The changing epidemiology of yellow fever and continued reports of rare but serious adverse events associated with yellow fever vaccine have drawn attention to the need to revisit criteria for the designation of areas with risk for yellow fever virus activity, and to revise the vaccine recommendations for international travel. WHO convened a working group of international experts to review factors important for the transmission of yellow fever virus and country-specific yellow fever information, to establish criteria for additions to or removal from the list of countries with risk for yellow fever virus transmission, to update yellow fever risk maps, and to revise the recommendations for vaccination for international travel. This report details the recommendations made by the working group about criteria for the designation of risk and specific changes to the classification of areas with risk for transmission of yellow fever virus.

Despite coronavirus disease 2019-related disruptions in controlling dengue, efforts need to be maintained to prevent vector-borne diseases during this pandemic. Although travel restrictions brought a global halt to mobility and therefore also a substantial decline of imported and travel-associated dengue, dengue will become dominant again in travel medicine as soon as international travel resumes.