Abstract ( n=254/250 words)   Background: The Janssen-Ad26.COV2.S vaccine is authorised for use in several countries with more than 30 million doses administered. Mild and severe allergic adverse events following immunisation(AEFI) have been reported. The aim of this report is to detail allergic reactions reported during the Sisonke phase 3B study in South Africa. Methods: A single-dose of the Ad26.COV2.S vaccine was administered to 477234 South African Healthcare Workers between 17 February and 17 May 2021. Monitoring of adverse events used a combination of passive reporting and active case finding. Telephonic contact was attempted for all adverse events reported as “allergy”. Anaphylaxis adjudication was performed using the Brighton Collaboration (BCC) and NIAID case definitions.  Results: A large cohort of South African healthcare workers received the Ad26.COV2.S vaccination. Only 250(0.052%) patients reported any allergic-type reaction(less than 1 in 2000), with four cases of adjudicated anaphylaxis (BCC level 1, n=3)(prevalence of 8.4 per million doses). All anaphylaxis cases had a prior history of drug or vaccine-associated anaphylaxis. Cutaneous allergic reactions were the commonest non-anaphylatic reactions and included: self-limiting, transient/localised rashes requiring no healthcare contact(n=91); or isolated urticaria and/or angioedema[n=70 median  onset 48(IQR 11.5-120) hours post vaccination] that necessitated healthcare contact(81%), antihistamine(63%), and/or systemic/topical corticosteroid(16%). All immediate (including adjudicated anaphylaxis) and the majority of delayed AEFI(65/69) cases resolved completely.   Conclusions: Allergic AEFI are rare following a single-dose of Ad26.COV with complete resolution in  all cases of anaphylaxis. Though rare, isolated, delayed onset urticaria and/or angioedema was the commonest allergic AEFI requiring treatment, with nearly half occurring in participants without known atopic disease.   Keywords: allergic reaction, anaphylaxis, COVID19 adenovirus vaccine; Janssen-Ad26.COV2.S vaccine, urticaria

Background Up to a quarter of inpatients in high-income countries self-report beta-lactam allergy (BLA), which if incorrect, can increase use of alternative antibiotics that impact on bacterial resistance.. The epidemiology of BLA in low- and middle-income African countries is unknown. Methods Point-prevalence surveys were conducted at seven hospitals (adult, pediatric, government and private-funded, district- and tertiary-level) in Cape Town, South Africa between April 2019 and June 2021. Ward prescription records and interviews were conducted to identify BLA patients. De-labeling was attempted at the tertiary allergy clinic at Groote Schuur hospital. Findings A total of 1486 hospital inpatients were surveyed (1166 adults; 308 children). Only 48 (3.2%) patients self-reported a BLA with a higher rate amongst private- versus government-funded hospitals [6.3% vs 2.8%, p=0.014]. Using the PEN-FAST tool, only 10.4% (5/48) of self reported BLA patients were classified as high risk for true penicillin hypersensitivity. Antibiotics were prescribed to 70.8% (34/48) of self reported BLA patients, with 64.7% (22/34) receiving a beta-lactam. Despite three attempts to contact patients for de-labelling at the allergy clinic, only 3/36 underwent in vivo testing, with no positive results and one patient proceeded toa negative oral challenge. Interpretation Unlike high-income countries, self-reported BLA is low amongst inpatients in South Africa. The majority of self-reported BLA were low risk for type 1 hypersensitivity, but out-patient de-labeling efforts were largely unsuccessful. Funding None