key: cord-0876322-k27v0evz authors: Kherabi, Yousra; Fiolet, Thibault; Rozencwajg, Sacha; Salaün, Jean-Philippe; Peiffer-Smadja, Nathan title: COVID-19 vaccine boosters: What do we know so far? date: 2021-10-09 journal: Anaesth Crit Care Pain Med DOI: 10.1016/j.accpm.2021.100959 sha: e7f411079a2e42b4f02bd9330fa4901e3e3bc31a doc_id: 876322 cord_uid: k27v0evz nan The most effective regimen for Coronavirus Infectious Disease 19 vaccination is still unknown as data keep evolving following the waning of immunity over time and the occurrence of new variants. Concerns about vaccine efficiency arose with the circulation of the Delta variant which has been associated with higher viral load and transmissibility (1) . Indeed, several in vitro studies reported a modest decrease in the response of neutralising antibodies to the Delta variant for mRNA vaccines (2, 3) . Furthermore, observational studies reported a decrease in the BNT162b2 (Pfizer-BioNTech) vaccine's effectiveness against infection from more than 90% before the spread of the variant (4,5) to 42-80% after (6) (7) (8) . Estimating vaccine effectiveness across studies and countries has been difficult since variants started circulating. Indeed, immunity due to vaccines and/or natural infection, population behaviour and public health policies vary tremendously and measures of effectiveness are impacted by these variations as well as by the waning of immunity over time. This decrease in immunity has been confirmed in several observational studies reporting a decrease in effectiveness against infection 5 to 6 months after the second dose, even though this decrease was less pronounced for hospitalisations or evolution to a severe form of the disease (9,10). Neutralising antibodies titres decreased over time for both mRNA vaccines and viral vector vaccines such as the Ad26.COV2-S vaccine (J&J/Janssen) (11) (12) (13) . Other studies, on the contrary, observed that mediated-cell immunity was sustained 6 months after the second dose (13, 14) . Therefore, the question of a third dose or booster has recently been raised but still remains questionable. First, several concordant analyses showed that a third dose was useful in inducing a boost in humoral response for patients with immunosuppression or cancer who had no detectable antibodies or low antibodies titres (15, 16) , and among healthy participants (17) . Regarding real-life data, Israel has provided the most extensive data regarding COVID-19 vaccines as the country has one of the fastest growing vaccine coverage, with half of its population receiving at least one dose by late February 2021. In order to counter a potential waning in immunity, Israel decided to respond to the Delta wave with a booster program, allowing people above 60 years of age to receive a third dose. (20) . The Com-COV study showed that mixing ChAdOx1-S (Oxford/AstraZeneca) and Pfizer/BioNTech vaccines with a 28-day prime-boost interval was safe and induced a higher immune response than the standard homologous dosing regimens (21) . Conclusion Administering a booster dose showed an improvement in humoral response, and real-life population data will soon be available for countries, which implemented this strategy in place. Nevertheless, making use of a booster is only an option for high-income countries and raises ethical questions. No global control of the pandemic is possible without equity in the supply of vaccines and leaving people unvaccinated across the world might currently be a more important threat than waning immunity. J o u r n a l P r e -p r o o f Increased transmissibility and global spread of SARS-CoV-2 variants of concern as at BNT162b2-elicited neutralization of B.1.617 and other SARS-CoV-2 variants Neutralising capacity against Delta (B.1.617.2) and other variants of concern following Comirnaty (BNT162b2, BioNTech/Pfizer) vaccination in health care workers Vaccine in a Nationwide Mass Vaccination Setting Impact and effectiveness of mRNA BNT162b2 vaccine against SARS-CoV-2 infections and COVID-19 cases, hospitalisations, and deaths following a nationwide vaccination campaign in Israel: an observational study using national surveillance data. The Lancet BNT162b2 and mRNA-1273 COVID-19 vaccine effectiveness against the Delta (B.1.617.2) variant in Qatar Impact of Delta on viral burden and vaccine effectiveness against new SARS-CoV-2 infections in the UK SARS-CoV-2 Delta VOC in Scotland: demographics, risk of hospital admission, and vaccine effectiveness. The Lancet Waning immunity of the BNT162b2 vaccine: A nationwide study from Israel Six-Month Effectiveness of BNT162B2 mRNA COVID-19 Vaccine in a Large US Integrated Health System: A Retrospective Cohort Study Social Science Research Network; 2021 août Durable Humoral and Cellular Immune Responses 8 Months after Ad26.COV2.S Vaccination Dynamics of antibody response to BNT162b2 vaccine after six months: a longitudinal prospective study Durability of mRNA-1273 vaccine-induced antibodies against SARS-CoV-2 variants Evidence of SARS-Cov-2-specific memory B cells six months after vaccination with BNT162b2 mRNA vaccine Antibody Response After a Third Dose of the mRNA-1273 SARS-CoV-2 Vaccine in Kidney Transplant Recipients With Minimal Serologic Response to 2 Doses Three Doses of an mRNA Covid-19 Vaccine in Solid-Organ Transplant Recipients SARS-CoV-2 Neutralization with BNT162b2 Vaccine Dose 3 Protection of BNT162b2 Vaccine Booster against Covid-19 in Israel Virological and serological kinetics of SARS-CoV-2 Delta variant vaccine-breakthrough infections: a multi-center cohort study Strong humoral immune responses against SARS-CoV-2 Spike after BNT162b2 mRNA vaccination with a sixteenweek interval between doses Safety and immunogenicity of heterologous versus homologous prime-boost schedules with an adenoviral vectored and mRNA COVID-19 vaccine (Com-COV): a single-blind, randomised, non-inferiority trial. The Lancet