COVID-19 has taken a severe toll on the global population through infections, hospitalizations, and deaths. Elucidating SARS-CoV-2 infection-derived immunity has led to the development of multiple effective COVID-19 vaccines and their implementation into mass-vaccination programs worldwide. After ~3 years, a substantial proportion of the human population possesses immunity from infection and/or vaccination. With waning immune protection over time against emerging SARS-CoV-2 variants, it is essential to understand the duration of protection, breadth of coverage, and effects on reinfection. This targeted review summarizes available research literature on SARS-CoV-2 infection-derived, vaccination-elicited, and hybrid immunity. Infection-derived immunity has shown 93–100% protection against severe COVID-19 outcomes for up to 8 months, but reinfection is observed with some virus variants. Vaccination elicits high levels of neutralizing antibodies and a breadth of CD4+ and CD8+ T-cell responses. Hybrid immunity enables strong, broad responses, with high-quality memory B cells generated at 5- to 10-fold higher levels, versus infection or vaccination alone and protection against symptomatic disease lasting for 6–8 months. SARS-CoV-2 evolution into more transmissible and immunologically divergent variants has necessitated the updating of COVID-19 vaccines. To ensure continued protection against SARS-CoV-2 variants, regulators and vaccine technical committees recommend variant-specific or bivalent vaccines.

Vaccination against infectious disease affords direct protection from vaccine-induced immunity and additional indirect protection for unvaccinated persons. A systematic review was conducted to estimate the indirect effect of COVID-19 vaccination. From PubMed and Embase, 31 studies were included describing the impact of original wild-type COVID-19 vaccines on disease transmission or viral load. Overall, study results showed the effectiveness of COVID-19 vaccination against SARS-CoV-2 transmission (range 16–95%), regardless of vaccine type or number of doses. The effect was apparent, but less pronounced against omicron (range 24–95% for pre-omicron variants versus 16–31% for omicron). Results from viral load studies were supportive, showing SARS-CoV-2 infections in vaccinated individuals had higher Ct values, suggesting lower viral load, compared to infections among the unvaccinated. Based on these findings, well-timed vaccination programs may help reduce SARS-CoV-2 transmission—even in the omicron era. Whether better-matched vaccines can improve effectiveness against transmission in the omicron era needs further study.

The rapid rollout of vaccines to combat the coronavirus disease 2019 (COVID-19) pandemic over the past 2 years has resulted in the use of various vaccine platforms and regional differences in COVID-19 vaccine implementation strategies. The aim of this narrative review was to summarize evolving COVID-19 vaccine recommendations in countries in Latin America, Asia, and Africa and the Middle East across various vaccine platforms, age groups, and specific subpopulations. Nuances in primary and booster vaccination schedules were evaluated, and the preliminary impact of such diverse vaccination strategies are discussed, including key vaccine effectiveness data in the era of Omicron-lineage variants. Primary vaccination rates for included Latin American countries were 71–94% for adults and between 41% and 98% for adolescents and children; rates for first booster in adults were 36–85%. Primary vaccination rates for adults in the included Asian countries ranged from 64% in the Philippines to 98% in Malaysia, with corresponding booster rates varying from 9% in India to 78% in Singapore; for adolescents and children, primary vaccination rates ranged from 29% in the Philippines to 93% in Malaysia. Across included African and Middle Eastern countries, primary vaccination rates in adults varied widely from 32% in South Africa to 99% in the United Arab Emirates; booster rates ranged from 5% in South Africa to 60% in Bahrain. Evidence from the regions studied indicates preference of using an mRNA vaccine as a booster on the basis of safety and effectiveness of observed real-world data, especially during circulation of Omicron lineages. Vaccination against COVID-19 remains of paramount importance to reduce the burden of disease; strategies to overcome vaccine inequity, fatigue, hesitancy, and misinformation and to ensure adequate access and supply are also important.

The aim of this study was to evaluate the epidemiological profile of invasive meningococcal disease (IMD) in Brazil, the first Latin American country to introduce the group C meningococcal conjugate vaccine (included in the vaccination schedule in 2010). A systematic review was conducted, covering the years 2005-2017, to identify epidemiological information on IMD and Neisseria meningitidis carriers in Brazil. Documents from the Brazilian Ministry of Health and two public databases were analyzed to determine annual incidence rates, absolute numbers of diagnosed cases, serogroups identified, the relative distribution of cases per serogroup, and the case fatality rate (CFR). Sixteen studies were selected. The incidence rate ranged from 0.88 to 5.3 cases per 100000 inhabitants per year. According to secondary data, the annual incidence of IMD in 2015 was highest in males <1year old (7.1/100000). The number of diagnosed cases declined significantly over the years. In the literature, IMD showed a CFR from 20.0% to 50.0%, and a higher CFR for serogroup W (17.8%). Secondary data showed an absolute reduction in meningitis-attributable deaths between 2007 and 2015; however, the CFR remained stable (11.1% in 2007 and 8.4% in 2015). In 2015, serogroup W showed the highest CFR (24.1%), followed by serogroups C (19.2%), B (17.7%), and Y (14.3%). Despite a reduction in cases, the CFR remained stable and similar in the different age groups, even for disease caused by different serogroups. The highest CFR was found to be associated with serogroup W.

The first case of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) reinfection, which can be caused by the same or different variant from the initial infection, was diagnosed on 25 August 2020 in Hong Kong [1–3]. Such cases were assumed to be rare early on in the pandemic, as most studies reported reinfection confirmed by […]

Influenza viruses cause 3-5 million severe cases and 300,000-600,000 deaths worldwide. Most of the disease burden is in Low- and Middle-Income Countries (LMICs) owing to factors such as high population density, infrastructure challenges, poor quality healthcare, lack of consistent recommendations, less prioritization of all high-risk groups, and prevalent use of trivalent influenza vaccines. Although influenza vaccines are effective in reducing the annual influenza disease burden, existing vaccines have several limitations. In this narrative review, we address the unmet needs of existing influenza vaccines in LMICs in Africa, Asia Pacific, Latin America and the Middle East and discuss the characteristics of novel vaccines in clinical development. We also describe features of a successful vaccination program that LMICs could emulate to improve their current vaccination coverage and reduce the public health burden of influenza.