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