SARS-CoV-2 IgG seropositivity after the severe Omicron wave of COVID-19 in Hong Kong

Abstract

The SARS-CoV-2 Omicron variant has led to a major wave of COVID-19 in Hong Kong between January and May 2022. Here, we used seroprevalence to estimate the combined incidence of vaccination and SARS-CoV-2 infection, including subclinical infection which were not diagnosed at the acute stage. The overall seropositive rate of IgG against receptor binding domain (anti-RBD IgG) increased from 52.2% in December 2021 to 89.3% in May 2022. The level of anti-RBD IgG was lowest in the 0–9 and ≥80 year-old age groups in May 2022. The seropositive rate of antibody against ORF8, which reflects the rate of prior infection, was 23.4% in May 2022. Our data suggest that although most individuals were either vaccinated or infected after the fifth wave, children and older adults remain most vulnerable. Public health measures should target these age groups in order to ameliorate the healthcare consequences of upcoming waves.

Effectiveness of BNT162b2 and CoronaVac COVID-19 vaccination against asymptomatic and symptomatic infection of SARS-CoV-2 omicron BA.2 in Hong Kong: a prospective cohort study

“…The provision of free rapid antigen tests to all enrolled participants helped to minimise the potential effect of changing testing policy and capacity on outcome ascertainment. The exclusion of 15·3% of individuals who were previously infected was consistent with the reported local seroprevalence against BA.2 of 7·3% before the fifth wave of SARS-CoV-2 in November to December, 2021, 27 and 23·4% after the peak of the fifth wave of infection in May, 2022, 28 and might have helped us avoid wrongly attributing protection to previous infection in the vaccine effectiveness analysis. Understanding the updated effectiveness of available vaccines against infection, including asymptomatic infection, in relation to the evolving omicron variants is essential for guiding vaccination policies and informing future vaccine development.…”

Real-world COVID-19 vaccine effectiveness against the Omicron BA.2 variant in a SARS-CoV-2 infection-naive population

“…In Hong Kong, a separate study of 873 hospital patient plasma specimens detected 43% were anti-N seropositive and 23% were anti-ORF8 seropositive by May 2022 (ref. 51 ). Another separate phylogenetic model of population IAR using GISAID sequences uploaded from multiple laboratories in Hong Kong as input also arrived at upper estimates between 33 and 49% (13–100%) by the week of 16 April 2022, which was similar to our mean estimate of 40% in the same week 52 .…”

Seroprevalence of Anti-SARS-CoV-2 Antibodies Following the Omicron BA.1 Wave

“…The wide spread of infections and gradual rise in vaccination coverage in the period covered in this study, although at a slower pace than in 2021, resulted in a high proportion of people with positive SARS-CoV-2 antibodies. In spring 2022, the seroprevalence of anti-S antibodies varied from 81.4% to 97.6%, depending mostly on the timing of serum sample collection, the age of the participants, and vaccination coverage [ 28 , 29 , 33 , 38 , 39 ]. The anti-S seroprevalence found in our study is in accordance with studies published so far.…”