Development of hybrid immunity during a period of high incidence of infections with Omicron subvariants: A prospective population based multi-region cohort study

BackgroundSeroprevalence and the proportion of people with neutralizing activity against SARS-CoV-2 variants was high in early 2022. Since it is unclear how immunity in the general population evolves, the aim of this study was to assess the development of functional and hybrid immunity in the general population during a period of high incidence of infections with Omicron variants. MethodsThis prospective population based multi-region cohort study is part of the Corona Immunitas research programme in Switzerland. In March 2022, we randomly selected individuals from the general population in southern (canton of Ticino) and north-eastern (canton of Zurich) Switzerland, who were assessed again in June/July 2022. We supplemented the June/July 2022 sample with a random sample from western Switzerland (canton of Vaud). We assessed SARS-CoV-2 specific IgG antibodies against spike and nucleocapsid proteins and the presence of SARS-CoV-2 neutralising antibodies against three variants (wildtype, Delta, Omicron). FindingsIn June/July 2022, seroprevalence was >98% in 2553 individuals from the general Swiss population. The proportion of individuals with neutralising antibodies against wildtype, Delta, and Omicron was 94.2%, 90.8%, and 84.9%, and at least 51% of the participants developed hybrid immunity. Individuals with hybrid immunity had, compared to those with only vaccine- or infection-induced immunity, highest levels of both, anti-spike IgG antibodies titres (4518 vs. 4304 vs. 269 WHO U/ml) and neutralisation capacity against wildtype (99.8% vs. 98% vs. 47.5%), Delta (99% vs. 92.2% vs. 38.7%), and Omicron (96.4% vs. 79.5% vs. 47.5%). InterpretationThis first study on functional and hybrid immunity in the general population after Omicron waves showed that SARS-CoV-2 has become endemic. The high levels of antibodies and neutralization in the general populations support the emerging recommendations of some countries where booster vaccinations are still strongly recommended for vulnerable persons but less strongly recommended for individuals in the general population. FundingThe Corona Immunitas research network is coordinated by the Swiss School of Public Health (SSPH+) and funded by fundraising of SSPH+ including funds of the Swiss Federal Office of Public Health and private funders (ethical guidelines for funding stated by SSPH+ were respected), by funds of the cantons of Switzerland (Vaud, Zurich, and Basel), and by institutional funds of the Universities. Study registrationISRCTN18181860 Research in contextO_ST_ABSEvidence before this studyC_ST_ABSWe searched Pubmed, Medline, Scopus and Web of Knowledge, for primary population-based studies prospectively assessing infection-, vaccine-induced, and hybrid immunity and the respective neutralising activity of antibodies against SARS-CoV-2 and its variants of concern. We included articles published between 1 January and 28 September 2022, without language restrictions, and retrieved 540 publications after deduplication. None of the screened studies measured the prevalence of immune response and neutralisation capacity prospectively in population-based, representative samples accounting for type of acquired immunity. Evidence from five studies, all conducted in non-representative, convenience and relatively small samples (N<254), and/or in sub-populations (e.g., healthcare workers and children), shows that hybrid immunity confers higher immune protection and exhibits better neutralising capacity compared to vaccine- and infection-induced immunity. Furthermore, one of the screened studies highlights that antibodies developed by individuals with hybrid immunity show the slowest decline over a period of 10 months. Added value of this studyWe took advantage of an ongoing cohort study on anti-SARS-CoV-2 seroprevalence conducted in a representative sample of the general Swiss population (N=2553) using standard, previously validated methods, to measure changes over time in seroprevalence, neutralisation capacity against wildtype and variants of concerns of the virus (i.e., ACE2r-block), waning of antibodies, and new infections. This is the first study, conducted in the general population and during the pandemic phase characterized by very high incidence of Omicron infections, to assess the extent of hybrid immunity (51%) and neutralising antibodies against the wildtype (94.2%), Delta (90.8%), and Omicron variants (84.9%). Our findings show that individuals with hybrid immunity, compared to those with only vaccine- or infection-induced immunity, had the highest levels of both anti-spike IgG antibodies titres and neutralisation capacity against wildtype, Delta, and Omicron variants. We also found that, from March to June/July 2022, anti-spike IgG antibodies remained stable in the general population (>96%), while anti-nucleocapsid IgG antibodies fluctuated due to their fast waning (7.3% of participants anti-nucleocapsid IgG antibodies became undetectable) and the parallel spread of Omicron infections (18.6% of participants acquired anti-nucleocapsid IgG antibodies). Implications of all the available evidenceBy mid-2022, SARS-CoV-2 has become endemic, and a majority of individuals developed hybrid immunity with high levels of neutralisation against the wildtype, Delta, and Omicron variants of SARS-CoV-2. Combined with existing evidence, our results indicate that hybrid immunity confers higher levels of neutralising activity compared to both vaccine-induced and infection-induced immunity. This study extends findings on the immunological protection conferred by hybrid immunity from sub-populations to the general population. The high levels of antibodies and neutralization in the general populations support the emerging recommendations of some countries where booster vaccinations are still strongly recommended for vulnerable persons but less strongly recommended for individuals in the general population. Monitoring the prevalence, waning, and neutralising activity of antibodies against potential new variants of concern in populations remains crucial.

Performance of RT-PCR on saliva specimens compared to nasopharyngeal swabs for the detection of SARS-CoV-2 in children: A prospective comparative clinical trial

BackgroundSaliva RT-PCR is an attractive alternative for the detection of SARS-CoV-2 in adults with much less known in children. MethodsChildren and adolescents with symptoms suggestive of COVID-19 were prospectively enrolled in a comparative clinical trial of saliva and nasopharyngeal (NP) RT-PCR between November and December 2020. Detection rates and sensitivities of saliva and NP RT-PCR were compared. Participants with discordant NP and saliva RT-PCR results including viral load (VL) were also analyzed. ResultOut of 405 patients enrolled, 397 patients had two tests performed. Mean age was 12.7 years (range 1.2-17.9). Detection rates were 22.9% (95%CI 18.8-27.1%) by saliva RT-PCR, 25.4% (21.2-29.7%) by NP RT-PCR, and 26.7% (22.4-31.1%) by any test. The sensitivity of saliva was 85.2% (78.2-92.1%) when using NP as the gold standard; in contrast, when saliva was considered the gold standard, the sensitivity of NP was 94.5% (89.8-99.2%).For a NP RT-PCR VL threshold of [≥]103 and [≥]104 copies/ml, sensitivity of saliva increases to 88.7% and 95.2% respectively. Sensitivity of saliva and NP swabs was respectively 89.5% and 95.3% in patient with symptoms less than 4 days (p=0.249) and 70.0% and 95.0% in those with symptoms [≥] 4 to 7 days (p=0.096). The 15 patients who had an isolated positive NP RT-PCR were significantly younger (p=0.034), had a lower NP VL (median 5.6x103 vs 3.9x107, p<0.001), and were not able to drool saliva at the end of the sampling (p=0.002). VLs were significantly lower with saliva PCR than with NP RT-PCR (median 8.7 cp/ml x104; IQR 1.2x104-5.2x105; vs median 4.0x107cp/ml; IQR 8.6x105-1.x108; p<0.001). ConclusionSaliva PCR shows diagnostic performances close to NP RT-PCR for SARS-CoV2 detection in most symptomatic outpatient children and adolescents.

Prevalence of SARS-CoV-2 in household members and other close contacts of COVID-19 cases: a serologic study in canton of Vaud, Switzerland

BackgroundUnderstanding community-based SARS-CoV-2 transmission is crucial to inform public health decisions. Research on SARS-CoV-2 transmission within households and other close settings using serological testing is scarce. MethodsWe invited COVID-19 cases diagnosed between February 27 and April 1, 2020 in canton of Vaud, Switzerland, to participate, along with household members and other close contacts. Anti-SARS-CoV-2 IgG antibodies were measured using a Luminex immunoassay. We estimated factors associated with serological status using generalized estimating equations. FindingsOverall, 219 COVID-19 index cases, 302 household members, and 69 other close contacts participated between May 4 and June 27, 2020. More than half of household members (57{middle dot}2%, 95%CI 49{middle dot}7-64{middle dot}3) had developed a serologic response to SARS-CoV-2, while 19{middle dot}0% (95%CI 10{middle dot}0-33{middle dot}2) of other close contacts were seropositive. After adjusting for individual and household characteristics, infection risk was higher in household members aged 65 or more than in younger adults (aOR 3{middle dot}63, 95%CI 1{middle dot}05-12{middle dot}60), and in those not strictly adhering to simple hygiene rules like hand washing (aOR 1{middle dot}80, 95%CI 1{middle dot}02-3{middle dot}17). The risk was lower when more than 5 people outside home were met during the semi-confinement, compared to none (aOR 0{middle dot}35, 95%CI 0{middle dot}16-0{middle dot}74). The individual risk of household members to be seropositive was lower in large households (22% less per each additional person). InterpretationWe find that, during semi-confinement, household members of a COVID-19 case were at very high risk of getting infected, 3 times more than close contacts outside home. This highlights the need to provide clear messages on specific protective measures applicable at home. For elderly couples, who were especially at risk, providing them external support for daily basic activities is essential. FundingCenter for Primary Care and Public Health (Unisante), Canton of Vaud, Leenaards Foundation, Fondation pour lUniversite de Lausanne. SerocoViD is part of Corona Immunitas coordinated by SSPH+.

Antigen rapid tests, nasopharyngeal PCR and saliva PCR to detect SARS-CoV-2: a prospective comparative clinical trial

BackgroundNasopharyngeal antigen Rapid Diagnostic Tests (RDTs) and saliva RT-PCR have shown variable performance to detect SARS-CoV-2. MethodsIn October 2020, we conducted a prospective trial involving patients presenting at testing centers with symptoms of COVID-19. We compared detection rates and performance of RDT, saliva PCR and nasopharyngeal (NP) PCR. ResultsOut of 949 patients enrolled, 928 patients had all three tests. Detection rates were 35.2% (95%CI 32.2-38.4%) by RDT, 39.8% (36.6-43.0%) by saliva PCR, 40.1% (36.9-43.3%) by NP PCR, and 41.5% (38.3-44.7%) by any test. For those with viral loads (VL) [≥]106 copies/ml, detection rates were 30.3% (27.3-33.3), 31.4% (28.4-34.5), 31.5% (28.5-34.6), and 31.6% (28.6-34.7%) respectively. Sensitivity of RDT compared to NP PCR was 87.4% (83.6-90.6%) for all positive patients and 96.5% (93.6-98.3%) for those with VL[≥]106. Sensitivity of STANDARD-Q(R), Panbio and COVID-VIRO(R) Ag tests were 92.9% (86.4-96.9%), 86.1% (78.6-91.7%) and 84.1% (76.9-89.7%), respectively. For those with VL[≥]106, sensitivities were 96.6% (90.5-99.3%), 97.8% (92.1-99.7%) and 95.3% (89.4-98.5%) respectively. Specificity of RDT was 100% (99.3-100%) compared to any PCR. RDT sensitivity was similar <4 days (87.8%) and [≥]4 days (85.7%) after symptoms onset (p=0.6). Sensitivities of saliva and NP PCR were 95.7% (93.1-97.5%) and 96.5% (94.1-98.1%), respectively, compared to the other PCR. ConclusionsThe high performance of RDTs allows rapid identification of COVID cases with immediate isolation of the vast majority of contagious individuals. RDT could be a game changer in primary care practices, and even more so in resource-constrained settings. PCR on saliva can replace NP PCR. ClinicalTrial.gov Identifier: NCT04613310

Qualitative Changes in the SARS-CoV-2 Antibody Response in the Post-Infection Phase Impact the estimates of infections in Population-Based Seroprevalence Studies

We have determined SARS-CoV-2-specific antibody responses in a cohort of 96 individuals with acute infection and in 578 individuals enrolled in a seroprevalence population study in Switzerland including three groups, i.e. subjects with previous RT-PCR confirmed SARS-CoV-2 infections (n=90), positive patient contacts (n=177) and random selected subjects (n=311). SARS-CoV-2 antibody responses specific to the Spike (S), in the monomeric and native trimeric forms, and/or the nucleocapsid (N) proteins were equally sensitive in the acute infection phase. Interestingly, as compared to anti-S antibody responses, those against the N protein appear to wane in the post-infection and substantially underestimated the proportion of SARS-CoV-2 infections in the groups of patient positive contacts, i.e. 10.9 to 32.2% reduction and in the random selected general population, i.e. up to 45% reduction. The overall reduction in seroprevalence targeting only anti-N IgG antibodies for the total cohort ranged from 9.4 to 31%. Of note, the use of the S protein in its native trimer form was more sensitive as compared to monomeric S proteins. These results indicate that the assessment of anti-S IgG antibody responses against the native trimeric S protein should be implemented to estimate SARS-CoV-2 infections in population-based seroprevalence studies.