The cytopathic effect was recorded after three times, as well as the serum virus neutralization titer (NT50) was thought as the reciprocal value of the best dilution that showed at least 50% protection of cells. dosage, Delta neutralization was discovered in 19% (??)-BI-D ( em n /em ?=?8/43) and 88% ( em n /em ?=?37/42) of COVID-19 naive and COVID-19 recovered topics, respectively. 90 days following the booster dosage, all NH citizens preserved and created an increased Delta neutralization ( em p /em ? ?00001). Prior to the booster dosage, Omicron neutralization was discovered in 5% ( em n /em ?=?2/43) and 55% ( em n /em ?=?23/42) of COVID-19 naive and COVID-19 recovered topics, respectively, and 90 days after, in 84% and 95%, respectively. Neutralizing titers to Omicron had been less than to Delta in both mixed teams using a 35-collapse reduction in comparison to Delta. Interpretation The booster dosage restores high neutralization titers against Delta in every NH residents, with a lesser level against Omicron in a big majority of individuals. Future research (??)-BI-D are warranted to assess if repeated BNT162b2 booster dosages or brand-new specific vaccines may be considered for protecting such fragile patients against Omicron and/or future SARS-CoV-2 variants. Funding French government through the Programme Investissement d’Avenir (I-SITE ULNE/ANR-16-IDEX-0004 ULNE) and the Label of COVID-19 National Research Priority (National Steering Committee on Therapeutic Trials and Other COVID-19 Research, CAPNET). strong class=”kwd-title” Keywords: BNT162b2 vaccine, Boost, SARS-CoV-2, Delta, Omicron, Older people, immunogenicity Research in context Evidence before this study The emergence of SARS-CoV-2 Omicron may expose immunocompromised subjects to a new variant with an increased transmissibility and potential immune evasion to current vaccines. Recent reports exhibited that two doses of a mRNA-based vaccine elicit poor neutralization to Omicron compared to Delta, while a third dose broadens neutralizing antibody responses against Omicron in healthy adults. Added value of this study Our work shows that a third dose of BNT162b2 remains effective at least three-month post-vaccination to neutralize Delta in nursing home residents, but that Omicron is usually less sensitive to neutralization. Implications of all evidence available Considering the partial immune escape to BNT162b2, further studies are necessary to assess if new specific vaccines or repeated BNT162b2 booster doses should be considered in the medium term. Alt-text: Unlabelled box Introduction Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged in late 2019 in (??)-BI-D China and has since then caused the coronavirus disease 2019 (COVID-19) pandemic. Nursing home (NH) residents display both a higher risk of severe COVID-19 and an age-related immune alteration (also called immunosenescence).1 Previous reports demonstrated a low postvaccination antibody and cellular response against SARS-CoV-2 in older people compared to more youthful.2,3 We notably reported that this antibody response and the functional T-Cell response to SARS-CoV-2 were impaired three months after initial SARS-CoV-2 BNT162b2 mRNA vaccination series (two doses) in NH residents, including the neutralizing response against the B.1.1.7 (Alpha) variant which was dominant in the first months of 2021.3 This data suggested that a third dose should be considered to improve protective immunity in this at-risk population. Since the summer time of 2021, numerous national health (??)-BI-D government bodies have recommended such a booster vaccination in older people and other immunocompromised subjects, but the Delta variant was already dominant at this time, and the efficiency of such vaccinal techniques against the (??)-BI-D current dominant variants of concern (VoC) B.1.617.2 (Delta) and B.1.1.529 (Omicron) needs to be Rabbit Polyclonal to WAVE1 assessed. Indeed, the SARS-CoV-2 distributing has been controlled thanks to vaccines and despite the emergence of successive computer virus variants. Recently, Omicron has been detected in South Africa, Botswana and in a traveler from South Africa in Hong Kong in November 2021.4 Compared to the previous VoC, Omicron displays numerous additional mutations modifying epitope sites within the receptor binding domain name (RBD) of the spike protein.5,6 Consequently, several reports logically demonstrated that neutralizing activity against Omicron was absent or very low for monoclonal antibodies, and for sera from convalescent or from double vaccinated people.5,7, 8, 9 Conversely, a third dose of mRNA based vaccine elicited humoral immunity capable of cross-neutralizing new variants.5,7 However, specific studies are warranted to assess immunogenicity of a booster strategy in immunocompromised and/or subjects at risk for severe COVID-19. The present study aimed to evaluate the prolonged immunogenicity offered by a third dose of BNT162b2 against Delta and Omicron variants, in boosted NH residents without or with COVID-19 prior to initial vaccination. Methods Study design and participants This was a prospective single-center study conducted at the Lille University or college Hospital, in the North of France. NH residents were included in the study before receiving the first 2 doses of BNT162b2 mRNA vaccine if they fulfilled the following inclusion criteria: age 65 years, consent to be vaccinated with BNT162b2 mRNA vaccine and eligibility for the third dose (booster vaccine), in absence of.