SARS-CoV-2 Infection Is at Herd Immunity in the Majority Segment of the Population of Qatar

Abstract

Background Qatar experienced a severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) epidemic that disproportionately affected the craft and manual worker (CMW) population who comprise 60% of the total population. This study aimed to assess ever and/or current infection prevalence in this population. Methods A cross-sectional population-based survey was conducted during July 26-September 09, 2020 to assess both anti-SARS-CoV-2 positivity through serological testing and current infection positivity through polymerase chain reaction (PCR) testing. Associations with antibody and PCR positivity were identified through regression analyses. Results Study included 2,641 participants, 69.3% of whom were <40 years of age. Anti-SARS-CoV-2 positivity was 55.3% (95% CI: 53.3-57.3%) and was significantly associated with nationality, geographic location, educational attainment, occupation, and previous infection diagnosis. PCR positivity was 11.3% (95% CI: 9.9-12.8%) and was significantly associated with nationality, geographic location, occupation, contact with an infected person, and reporting two or more symptoms. Infection positivity (antibody and/or PCR positive) was 60.6% (95% CI: 58.6-62.5%). The proportion of antibody-positive CMWs that had a prior SARS-CoV-2 diagnosis was 9.3% (95% CI: 7.9-11.0%). Only seven infections were ever severe and one was ever critical—an infection severity rate of 0.5% (95% CI: 0.2-1.0%). Conclusions Six in every 10 CMWs have been infected, suggestive of reaching the herd immunity threshold. Infection severity was low with only one in every 200 infections progressing to be severe or critical. Only one in every 10 infections had been previously diagnosed suggestive of mostly asymptomatic or mild infections.

SARS-CoV-2 seroprevalence in the urban population of Qatar: An analysis of antibody testing on a sample of 112,941 individuals

“…The above results indicate that <20% of the urban population of Qatar, which constitutes 40% of the total population and includes nearly all older adults, manifests evidence of prior infection. This seroprevalence is substantially less than that in the CMW part of the population, which was estimated recently in a nationwide survey at 55.3% (Al-Thani et al, 2021), with the leading risk factor being living in a large shared accommodation (Al-Thani et al, 2021;Abu-Raddad et al, 2021a;Jeremijenko et al, 2021;Al Kuwari et al, 2020).…”

“…This finding suggests that the lockdown and imposed social and physical distancing restrictions have been more successful in slowing transmission in the urban population compared to the CMW population. Building on the totality of evidence on the Qatar epidemic (Abu-Raddad et al, 2021a; Al Al-Thani et al, 2021;Ayoub et al, 2021;Jeremijenko et al, 2021), this appears to be due to the dwelling structure, in that the urban population lives mostly in single-unit or family households that each includes a small number of individuals. Meanwhile, the CMW population lives mostly in large shared accommodations that each includes a large number of individuals.…”

“…These are probably not due to biological differences but to differences in the likelihood of exposure to the infection. Indeed, a small proportion of the specimens tested in this study belonged to CMWs who had a higher risk of exposure to the infection than the urban population (Al-Thani et al, 2021;Jeremijenko et al, 2021). While Hamad Medical Corporation (HMC) provides healthcare primarily to the urban population and other providers cater to the CMW population, HMC is a main tertiary care center in Qatar and was also the nationally designated provider for COVID-19 healthcare needs.…”

“…Thus, it is likely that a small proportion of specimens, which cannot be estimated precisely, were drawn from CMWs who were hospitalized for COVID-19 or other reasons. This may explain the higher antibody positivity of young Bangladeshi, Indian, and Nepalese men (Table 1), who form the bulk of the CMW population (Al-Thani et al, 2021;Jeremijenko et al, 2021). This may also explain the higher seroprevalence in the blood specimens drawn during inpatient or emergency clinical care, which are more likely to be COVID-19 related, than those drawn during outpatient or home care/follow-up consultation clinical care (Table 1).…”

“…Qatar has a unique socio-demographic structure, in which single-unit and family households, including children, adults, and/or older adults, account for only 40% of the total population, with adults in this ''urban population'' often being part of the professional or service workforce ( Infection transmission in Qatar was first documented among CMWs on March 6, 2020 (Al , who were subsequently most affected by this epidemic (Abu-Raddad et al, 2021a). A recently completed nationwide, population-based survey assessing ''every'' infection among the CMW population found that six out of every ten persons had detectable antibodies against SARS-CoV-2 (Al-Thani et al, 2021;Jeremijenko et al, 2021), suggesting that this population is at or near herd immunity for the variants circulating at this time (Jeremijenko et al, 2021;Anderson et al, 2020;Britton et al, 2020). In the present study, the first objective was to assess the level of infection exposure among the rest of the population of Qatar, that of the ''urban population'' of this country.…”