Introduction
The ongoing global effort to vaccinate an estimated 60% of the human
population started in December 2020. In just six months, mass vaccine
campaigns have seen approximately 5 billion doses of COVID19 vaccines
administered and more than a quarter of the world population having
received at least one dose (1). There are currently 13 different
vaccines in use, with three major emergency authorised platforms
including: inactivated SARsCoV2 virus (Sinopharm and Sinovac-CoronaVac);
adenoviral-vectored (ChadOx/AstraZeneca and Ad26.COV2.S); and the mRNA
vaccines (Moderna mRNA 1273 and Pfizer/BionNtech Comirnaty) – the
latter two technologies with either little or no prior large scale human
use in other infections. The mass use of these novel vaccine
technologies has meant increased reporting of uncommon and rare adverse
events following immunisation (AEFI), including immune-mediated events
such as Guillain-Barré syndrome and anaphylaxis (2). Large cohort
studies such as Sisonke, a phase 3B study of the Ad26.COV2.S in South
African (SA) Healthcare workers (HCW), are thus invaluable to provide
more detailed information about these uncommon adverse events of special
interest (AESI).
Allergic AEFI are well-known and
reported with almost all registered vaccines, with the prevalence of
anaphylaxis in most vaccine safety surveillance systems
~1 in a million doses (3, 4). Soon after the emergency
authorisation of mRNA COVID19 vaccines an increased prevalence of
anaphylaxis was noted with this novel platform, with prevalence
estimates from 2-100 per million doses (2, 5, 6), and self-reported
allergic reactions in ~2% of vaccine recipients (2).
Few reports of anaphylaxis following ChAdOx1-S adenovirus vaccine are
available, with prevalence estimates of 0.3-33 per million doses (5). No
anaphylactic events occurred in the ENSEMBLE trials of the Ad26.COV2.S
(7, 8), with only one post-marketing surveillance study reported to
date(9). There are several reports of self-limiting, delayed, large
local allergic reactions surrounding the injection site following the
Moderna mRNA 1273 vaccine (10), but the prevalence, spectrum and
outcomes of delayed allergic reactions to other COVID19 vaccines have
not been reported. Thus, we aimed to detail the spectrum of immediate
and delayed allergic AEFI reported following Ad26.COV2.S vaccination in
a large cohort of SA HCWs.