key: cord-0958968-4rsvcbnz
authors: Reynolds, C. J.; Swadling, L.; Gibbons, J. M.; Pade, C.; Jensen, M.; Diniz, M. O.; Schmidt, N. M.; Butler, D. K.; Amin, O. E.; Bailey, S. N. L.; Talyor, S.; Jones, J.; Jones, M.; Lee, W. Y. J.; Rosenheim, J.; Chandran, A.; Joy, G.; Di Genova, C.; Temperton, N. J.; Lambourne, J.; Cutino-Moguel, T.; Andiapen, M.; Fontana, M.; Smit, A.; Semper, A.; O'Brien, B.; Chain, B.; Brooks, T.; Manisty, C.; Treibel, T.; Moon, J.; COVIDsortium Investigators,; Noursadeghi, M. C.; COVIDsortium Immune correlates network,; Altmann, D. M.; Mani, M. K.; McKnight, A.; Boyton, R. J.
title: Healthcare workers with mild / asymptomatic SARS-CoV-2 infection show T cell responses and neutralising antibodies after the first wave
date: 2020-10-14
journal: nan
DOI: 10.1101/2020.10.13.20211763
sha: 4bbf792b06356fb408cba7710a80493a35da3153
doc_id: 958968
cord_uid: 4rsvcbnz

Studies of adaptive immunity to SARS-CoV-2 include characterisation of lethal, severe and mild cases. Understanding how long immunity lasts in people who have had mild or asymptomatic infection is crucial. Healthcare worker (HCW) cohorts exposed to and infected by SARS-CoV-2 during the early stages of the pandemic are an invaluable resource to study this question. The UK COVIDsortium is a longitudinal, London hospital HCW cohort, followed from the time of UK lockdown; weekly PCR, serology and symptom diaries allowed capture of asymptomatic infection around the time of onset, so duration of immunity could be tracked. Here, we conduct a cross-sectional, case-control, sub-study of 136 HCW at 16-18 weeks after UK lockdown, with 76 having had laboratory-confirmed SARS-CoV-2 mild or asymptomatic infection. Neutralising antibodies (nAb) were present in 90% of infected HCW sampled after the first wave; titres, likely to correlate with functional protection, were present in 66% at 16-18 weeks. T cell responses tended to be lower in asymptomatic infected HCW than those reporting case-definition symptoms of COVID-19, while nAb titres were maintained irrespective of symptoms. T cell and antibody responses were discordant. HCW lacking nAb also showed undetectable T cells to Spike protein but had T cells of other specificities. Our findings suggest that the majority of HCW with mild or asymptomatic SARS-CoV-2 infection carry nAb complemented by multi-specific T cell responses for at least 4 months after mild or asymptomatic SARS-CoV-2 infection.

pandemic controls (Fig. 1d, Extended Data Fig. 1c, d; Extended Data Table 1a, b) . 126

The OLP pools (utilising increased cell numbers) showed detectable T cell 127 responses in the PCR negative, S1 IgG negative HCW group (Extended Data Fig. 128 5 In addition to IFNγ SFC, we explored other cytokines indicative of non-Th1 subset 135 polarisation by screening supernatants from Spike and NP protein-stimulated 136

ELISpots; they showed no evidence of 5, 13, 17 or 23 (Extended Data Fig. 1e) . 137

In line with previous observations of SARS-CoV-2 T cells and ageing 23 , T cell 139 responses in HCW (n=75) with laboratory confirmed SARS-CoV-2 correlated with 140

age. There was a correlation with increasing age and T cell responses against Spike 141 MEP2, NP1 OLP and ORF3a/7a MEP (Extended Data Fig. 2a-d) . Broken down by 142 age and gender, T cell immunity to Spike increased with age in males (Spike protein; 143 r=0.522, p=0.006) (Extended Data Fig. 2e ). We found no differences in T cell 144 responses associated with ethnicity (Extended Data Fig. 3a ,b). T cell immunity to M 145 MEP, ORF3a/7a MEP and ORF3a OLP was higher in males compared to females 146 (Extended data Fig. 3c,d) . 147

148

The majority of HCW in this cohort with laboratory confirmed SARS-CoV-2 infection 150 had detectable S1 IgG and/or NP IgG/IgM (97%) during follow-up. Peak antibody 151 level during 16-18 week follow-up (Fig2a) was considered to be a useful marker of 152 humoral immune activation in each HCW. Some studies of nAb responses in severe, 153 mild and asymptomatic disease have highlighted rapid waning of nAb within weeks 16, 24 , with others finding a more sustained neutralising response [25] [26] [27] . We analysed 155 the nAb response in HCW at 16-18 weeks after UK lockdown and found that 90% 156 could neutralise pseudotype virus. There was a range of nAb titres detectable, with 157 66% having an IC50 titre of >200 ( Fig. 2b-c) , a correlate of protection in SARS-CoV-158 2 based on viral challenge in macaque studies 28 . Ten percent of HCW with 159 laboratory-confirmed SARS-CoV-2 infection demonstrated no detectable neutralising 160 response ( Fig. 2b-c) . Typical nAb profiles in the high (IC50 ≥200), low and none (IC50 ≤49) categories are shown (Extended Data, Fig 4a) . The nAb 162 response positively correlated with peak S1 IgG and peak NP IgG/IgM (Fig. 2d) . 163

Peak S1 IgG tended to be lower in those reporting non-case defining symptoms and 164 those who were asymptomatic compared to those with case-definition symptoms 165 (Fig. 2e) . However, the nAb IC50 titre at 16-18 weeks after lockdown was maintained 166 at a similar level across these three symptom groups (Fig. 2f) . Eighty-eight percent 167 6 of HCW aged ≥50y developed nAb at an IC50 of >200 compared with 59% of 168 younger HCW aged 24-49y; p=0.041 (Fig. 2g) . Peak S1 IgG Ab and nAb IC50 169 increased with age in females (Fig 2h) . We looked in more detail at comparative 170 features of infected individuals in the HCW cohort who did or did not show a nAb 171 response at 16-18 weeks (Extended Data, Fig. 4b-d) ; we cannot discount the 172 possibility that these individuals may have shown an earlier response that had 173 waned by 16-18 weeks. These 7 HCW with no nAbs spanned an age-range of 26-174 53y and tended to be at the lower end of the HCW age-range. Although this sub-175 study was not powered to investigate stratified demographic differences, we looked 176 at features such as gender, ethnicity, clinical role or location, use of personal 177 protective equipment (PPE) or symptom profile and found no difference between 178 those that made nAb and those that did not, though there was a trend to more male 179 non-neutralisers. 180

To better understand complementarity between nAb and T cells, we next compared 183 the T cell, S1 IgG and nAb responses in individual HCW. T cell responses to Spike 184 and NP protein correlated with peak S1 IgG titre, but with weak correlation 185 coefficients partly attributable to lack of T cell responses in some HCW with positive 186 antibody titres to Spike and NP (Fig. 3a; blue box in Extended Data Figs. 5a, d) . 187

Correlations between peak NP IgG/IgM titre and T cell responses to Spike and NP 188 protein showed similar results (Extended Data Fig. 6a ). Just over half HCW were 189 discordant for T cell and S1 IgG responses, making no T cell response to Spike 190 protein and 15% made no T cell response to NP(Extended Data Fig. 5a-f ). While we 191 found no differences in terms of age, gender, ethnicity, symptom profile, clinical role 192 or PPE use, there tended to be more non-responders among Black, Asian and 193 minority ethnic (BAME) HCW. 194 195 In Fig. 2b , we showed that 10% of infected HCW lacked detectable nAb at 16-18 196 weeks after UK lockdown. To understand the complementarity between T cell and 197 nAb responses in individual HCW, we analysed responses of all HCW ranked either 198 by nAb IC50 titre or cumulative T cell response. We first arrayed HCW responses 199 ranked by magnitude of nAb response (Fig. 3b) . Neutralisation IC50 values for all 200 HCW were plotted in relation to our indicative, protective cut-off value of >200 (dotted 201 7 horizontal red line in lower panel). HCW lacking detectable nAb are indicated by 7 202 black arrows on the left. Their cumulative T cell response frequencies against viral 203 antigens are shown in the panel above and are relatively low. Relating lack of nAbs 204 to T cell responses to different specific antigens we show that none of the 7 HCW 205 without detectable nAb make a T cell response to Spike protein (Extended data Fig  206   6b ). The addition of data from Spike MEP pools (potentially encompassing CD8 207 responses as well) revealed low T cell responses to Spike in 4/7 HCW lacking a nAb 208 response (Extended data Fig 6c) . Exploring T cell responses to NP protein and NP, 209 M, and ORF3a/7a MEP pools showed 5/7 HCW without detectable nAb making a T 210 cell response (Extended data Fig 6d) . Furthermore, there were OLP T cell responses 211 in 5/7 HCW lacking nAb (Extended data Fig 6e) . Thus HCW lacking nAb tend to lack 212 responses to Spike while maintaining low frequency T cells to other specificites. 213

Examining the converse, we then arrayed HCW responses ranked by magnitude of 215 cumulative T cell response (Fig 3c) . From this plot, HCW with the lowest cumulative 216 T cell response (to the left of the plot) have a range of nAb responses from none to 217 >200 IC50. One young, asymptomatic, female HCW with a good peak S1 IgG titre 218 had no T cell response to any antigens tested but made nAbs with a titre of 143, 219 which may be insufficient for functional protection (Fig 3b, c indicated by +). Another 220 female HCW with a good S1 IgG titre, also had no T cell response to any antigens 221 tested, but made nAbs with a titre of 747 (Fig 3b, c indicated by *). Assessing T cell 222 responses ranked simply on the basis of presence or absence of recognition of 223 proteins and pools (rather than magnitude of response) indicates that those lacking a 224 nAb response (black arrows) showed T cell responses against 2 to 5 antigens 225 (Extended data Fig 6f) . Taken together, the data show discordance of nAb and T cell 226 responses in individual HCW. 227

Of the 76 HCW studied with mild or asymptomatic laboratory-confirmed SARS-CoV-229 2 infection, 64% had one or more case-defining symptoms, 25% had non-case-230 defining symptoms and 11% were asymptomatic. Looking at T cell immunity and nAb 231 levels across these symptom-stratified groups at 16-18 weeks, T cell responses 232 tended to be higher in infected HCW with case defined symptoms. Responses to M 233 MEP and ORF3a OLP were significantly higher in HCW reporting case definition 234 symptoms than those that were asymptomatic (Extended Data Fig. 7a, b) . 235 8 Importantly, there was no significant fall in nAb titres across case-defining, non-case-236 defining symptoms and asymptomatic HCW groups ( Fig. 2d) Much debate has focused on the possibility that the Ab response to SARS-CoV-2 244 may be short-lived, while T cell recognition may be strong, durable, and more 245 common 14, 16, 17, 23, 27, 29 . Mild or asymptomatic infection are very common but are not 246 usually diagnosed contemporaneously, making assessment of the durability of 247 immunity in this common group challenging. Here we describe a cross-sectional 248 study of an exposed HCW cohort at 16-18 weeks after UK lockdown who had mild or 249 asymptomatic infection picked up by repeated PCR and serological testing. This 250 cohort shows variable T cell responses across the viral proteome sampled, with only 251 two HCW with lab-confirmed COVID-19 showing no detectable T cell response 252 across all the platforms tested. In this study, 90% of HCW with asymptomatic or mild 253 COVID-19 had nAb at 16-18 weeks after UK lockdown and 66% had titres >200. In 254 light of some reports of rapid waning of nAbs this result was surprising 15-17, 24,29 . Here 255 we show a complex pattern of T cell and nAb responses for individual HCW. 256

Analysis of nAbs shows that the majority of laboratory confirmed SARS-CoV-2 257 infected HCW with no symptoms or only mild disease had relatively high nAb IC50 at 258 16-18 weeks after UK lockdown. These IC50s were in the same range as those 259 defined as conferring functional protection in macaque challenge studies 28 . In terms 260 of neutralisation observations in humans, a study of SARS-CoV-2 susceptibility 261 during an outbreak on a fishing vessel indicated a lack of infection in those showing 262 a prior nAb titre (IC50) >1/160 30 . In infection by SARS-CoV-1, nAbs are often lost by 263 1-2 years after infection 19,31 , whereas T cell responses can persist for up to 17y after 264 SARS-CoV-1 3 . Longitudinal follow-up of nAb versus T cell kinetics in the 265 COVIDsortium cohort will illuminate T cell and nAb trajectories over time. 266

In terms of severe COVID-19 risk, two of the strongest factors identified have been 268 gender and age 32 . We found a positive correlation between both S1 IgG Ab level and 269 . CC-BY-NC-ND 4.0 International license It is made available under a perpetuity.

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The copyright holder for this this version posted October 14, 2020. . 9 nAb IC50 with age in female study participants. Other observations have suggested 270 a higher T cell response to mitogens in females with acute hospitalised COVID-19 33 ; 271 we observed higher memory T cell responses to Spike antigen in older males at 16-272 18 weeks after UK lockdown. Thus, in this asymptomatic/mild cohort of HCW, the 273 nAb response increases significantly with age in females, while it is the T cell 274 response that increases significantly with age in males. 275

A cautionary note about the ephemeral nature of adaptive immunity to coronaviruses 277 comes from data for annual reinfections with the four seasonal coronaviruses and 278 emerging data for reinfection by SARS-CoV-2 34,35 . Some studies have raised 279 concern about the durability of serum antibodies and B cell memory, with data 280 pointing towards impaired germinal centre reactions in severe acute . 281

Other studies have focused on the potential for rapid waning of nAb after mild SARS-282

CoV-2 infection 14,15 . However we find nAb detectable in the majority of HCW 283 sampled 16-18 weeks after mild/asymptomatic infection. Some T cell data indicates 284 that even asymptomatic people and household contacts develop low-frequency T 285 cell responses, in line with results from the HCW without laboratory confirmed 286 infection using one of our platforms with higher T cell numbers 6 . We show here that 287 infected HCW can display highly heterogeneous T cell recognition of epitopes from 288 diverse SARS-CoV-2 structural and non-structural proteins, but it is not yet possible 289 to decode the differential impacts of these responses for protection. Analysis of T cell 290 response repertoire in convalescent, hospitalised COVID-19 patients argues that 291 breadth of T cell response is a marker of mild disease 36 . 292

In summary, this study of HCW with laboratory confirmed SARS-CoV-2 infection 294 finds that in the majority of these working adults there is immunity at 16-18 weeks 295 comprising nAb (often at a level likely to protect), usually complemented by multi-296 specific T cell responses. Understanding protective immunity in the population will 297 require simultaneous scrutiny of T cell and antibody responses. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint

The copyright holder for this this version posted October 14, 2020 . . https://doi.org/10.1101 /2020 hospitals during an early phase of the pandemic. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint

The copyright holder for this this version posted October 14, 2020. collection at baseline and weekly follow-up for 15w from the start of each cohort. 434

Participants were asked to provide details and timing of symptoms in the 3 months 435 prior to baseline, and for those who were unable to attend follow-up visits (due to 436 shift rostering, annual leave or self-isolation), the reason for non-attendance was 437 collected, to ensure capture of information regarding isolation due to participant 438 symptoms or household contacts. On return from self-isolation with symptoms, 439 . CC-BY-NC-ND 4.0 International license It is made available under a perpetuity.

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The copyright holder for this this version posted October 14, 2020. . 14 convalescent samples were collected. Further follow-ups at 6 and 12 months are is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint

The copyright holder for this this version posted October 14, 2020. .

'case-defining' (fever, new continuous dry cough or a new loss of taste or smell), 474 'non-case-defining' (specific symptoms other than case-defining symptoms, or 475 unspecified symptoms), or asymptomatic (no symptoms reported were asymptomatic at baseline, during 16-week follow-up or in the 3 months prior to 496 baseline. A second age, gender, and ethnicity matched subgroup of sixty HCW were 497 recruited (mean age 39y, 37% male) who were SARS-CoV-2 PCR negative and 498 negative for Spike IgG (Euroimmun ELISA) and NP IgG/IgM antibody (Roche 499 Elecsys) tests throughout the 16-week follow-up. However, forty-four percent 500 reported one or more case defining COVID-19 symptoms, 41% non-case defining 501 symptoms and 15% were asymptomatic at baseline, during 16-week follow-up and in 502 the 3 months prior to baseline. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint

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Peripheral blood mononuclear cells (PBMC) were isolated from heparinized blood 508 samples using Pancoll (Pan Biotech) or Histopaque®-1077 Hybri-Max TM (Sigma-509

Aldrich) density gradient centrifugation in SepMate™ tubes (Stemcell) according to 510 the manufacturer specifications. Isolated PBMCs were cryopreserved in fetal calf 511 serum containing 10% DMSO and stored in liquid nitrogen. 512

Whole blood samples were collected in SST vacutainers (VACUETTE® #455092) 514 with inert polymer gel for serum separation and clot activator coating. After 515 centrifugation at 1000 X g for 10 minutes at room temperature, serum layer was 516 aliquoted and stored at -80 C for specific SARS-CoV-2 Ab titre detection by ELISA 517

and for SARS-CoV-2 Spike pseudotyped virus neutralisation assays. 518

Anti-SARS-CoV-2 S1 IgG ELISA (EUROIMMUN) was performed on a Stratec 520

Biomedical Gemini automated ELISA platform as described. The optical density was 521 detected at 450nm, and a ratio of the reading of each sample to the reading of the 522 calibrator included in the kit was calculated for each sample. An OD ratio of ≥1.1 was 523 interpreted as positive for S1 antibodies by manufacturer's recommendation. 524

Elecsys® Anti-SARS-CoV-2 nucleocapsid total Ab ELISA (ROCHE) was performed 525 as described. Results are reported as numeric values in the form of a cut-off index 526 (COI; signal sample/cut-off) as well as in the form of qualitative results non-reactive 527 (COI < 1.0; negative) and reactive (COI ≥ 1.0; positive). 528

The SARS-CoV-2 S1 Spike antigen and Nucleoprotein was obtained from the Centre is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint

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Pools of 13-20mer peptides based on the protein sequences of SARS-CoV-2 S1 535 (Spike), nucleoprotein (NP), membrane (M) and open reading frames 3a and 7a 536 (ORF3a/7a) described previously were synthesized 4 (GL Biochem Shanghai Ltd, 537

China). To stimulate PBMC, separate pools of sequences for Spike (18 peptides), 538 NP (10 peptides), M (6 peptides) and ORF3a/7a (7 peptides) were used, see 539

Extended Data Table 2a) . A second mapped epitope pool of SARS-CoV-2 S1 540 peptides (Spike MEP2) based on alignment of all sequences of published SARS-541

CoV-1 epitopes (www.iedb.org; search criteria: positive assays only, T cells assays, 542 host: human) with the Spike-SARS-CoV-2 sequence and 15-mer peptides 543 synthesised to cover the homologous sequences. In addition, we synthesised 15-544 mer peptides covering the predicted SARS-CoV-2 Spike epitopes 3 to give a total of 545 55 peptides in this pool (Spike MEP2), see Extended Data Table 2b 

Unless otherwise stated, culture medium for human T cells was sterile 0.22µM 554 filtered RPMI medium (GibcoBRL) supplemented with 10% by volume heat 555 inactivated (1h, 64°C) fetal calf serum (FCS; Hyclone, and 1% by volume 100x 556 penicillin and streptomycin solution (GibcoBRL). 557

For experiments involving T cell stimulation with proteins or MEP peptide pools, pre-558 coated ELISpot plates (Mabtech 3420-2APT) were washed x4 with sterile PBS and 559

were blocked with R10 for 1h at room temperature. 200,000 PBMC were seeded in 560 R10/well and were stimulated for 18-22h at 37°C with 5%CO 2 with SARS-CoV-2 561 recombinant proteins (10µg/ml) or MEP pools (10µg/ml/peptide). Internal plate 562 . CC-BY-NC-ND 4.0 International license It is made available under a perpetuity.

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The copyright holder for this this version posted October 14, 2020. . https://doi.org/10.1101/2020.10.13.20211763 doi: medRxiv preprint controls were R10 alone (without cells) and anti-CD3 (Mabtech mAb CD3-2). At the 563 end of the stimulation period, cell culture supernatants were collected and stored for 564 later cytokine analysis by Luminex. ELISpot plates were developed with human 565 biotinylated IFNγ detection Ab, directly conjugated to alkaline phosphatase (7-B6-1-566 ALP, Mabtech; 1µg/ml), diluted in PBS with 0.5% FCS, incubating 50µl/well for 2h at 567 room temperature. This was followed by 50µl/well of sterile filtered BCIP/NBT-plus 568

Phosphatase Substrate (Mabtech) for 5 minutes at room temperature. Plates were 569 washed in ddH20 and left to dry completely before being read on AID-ELISpot plate 570 reader. For experiments involving T cell stimulation with OLP peptide pools and 571

Spike MEP2 pool ELISpot plates (AID classic ELISpot plate reader (Autoimmun 572

Diagnostika GMBH, Germany) were coated with human anti-IFNγ Ab (1-D1K, 573

Mabtech; 10µg/ml) in PBS overnight at 4°C. Plates were washed x6 with sterile PBS 574 and were blocked with R10 for 2h at 37°C with 5% CO 2 . PBMC were thawed and 575 rested in R10 for 3h at 37 °C with 5%CO 2 before being counted. 400,000 PBMC 576 were seeded in R10/well and were stimulated for 16-20h with SARS-CoV-2 OLP 577 pools or Spike MEP2 pool (2µg/ml/peptide). Internal plate controls were R10 alone 578 (without cells) and two DMSO wells (negative controls), concanavalin A (ConA, 579 positive control; Sigma-Aldrich) and FEC (HLAI-restricted peptides from influenza, 580

Epstein-Barr virus, and CMV; 1µg/ml). ELISpot plates were developed with human 581 biotinylated IFN-γ detection antibody (7-B6-1, Mabtech; 1µg/ml) for 3h at room 582 temperature, followed by incubation with goat anti-biotin alkaline phosphatase 583 (Vector Laboratories; 1:1000) for 2h at room temperature, both diluted in PBS with 584 0.5% BSA by volume (Sigma-Aldrich), and finally with 50µl/well of sterile filtered 585 BCIP/NBT Phosphatase Substrate (ThermoFisher) for 7 minutes at room 586 temperature. Plates were washed in ddH20 and left to dry overnight before being 587 read on an AID classic ELISpot plate reader (Autoimmun Diagnostika GMBH, 588

Germany). 589

Analysis of ELISpot data was performed in Microsoft Excel. The average of two R10 590 alone wells or DMSO (Sigma-Aldrich) wells was subtracted from all peptide 591 stimulated wells and any response that was lower in magnitude than 2 standard 592 deviations of the sample specific control wells was not considered a peptide specific 593 response. Results were expressed as difference in (delta) spot forming cells per 10 6 594 19 excluded the results if negative control wells had >100 SFU/10 6 PBMC or positive 596 control wells (ConA or anti-CD3) were negative. Results were plotted using Prism v. 597 7.0e and 8.0 for Mac OS (GraphPad). 598

Concentrations of IL-4, IL-5, IL-13, IL-17a and IL-23 were measured by multiplex 600 is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint

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The copyright holder for this this version posted October 14, 2020. . https://doi.org/10.1101/2020.10.13.20211763 doi: medRxiv preprint linear regression method was used to determine the dilution fold that neutralised 654 50% (IC50). 655

Data was assumed to have a non-Gaussian distribution. Non-parametric tests were 657 is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint

The copyright holder for this this version posted October 14, 2020. The funders had no role in study design, data collection, data analysis, data 706 interpretation, or writing of the report. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint

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The authors declare no competing interests. 728 . CC-BY-NC-ND 4.0 International license It is made available under a perpetuity.

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The copyright holder for this this version posted October 14, 2020. . https://doi.org/10.1101/2020.10.13.20211763 doi: medRxiv preprint Extended Data Figure 5 .

Demographic characteristics of health care workers with laboratory-confirmed SARS-CoV-2 infection but no T cell response to Spike or NP protein at 16-18 weeks after UK lockdown: a) Correlation between peak S1 IgG Ab titre and T cell response to Spike protein in HCW with laboratory-confirmed SARS-CoV-2 infection, coloured by symptom group: HCW who had > 1 COVID-19 case definition symptoms (Red), non-case definition symptoms (Blue) or were asymptomatic (Grey). HCW with no T cell response to Spike protein are within the blue box.

b) The age in years of HCW for whom a T cell response to Spike protein was detected (top) or was not (bottom). c) Proportion of HCW with a T cell response to Spike protein (top row), or no T cell response to Spike protein (bottom row) stratified by the demographic characteristics of gender, ethnicity, clinical role, clinical location, PPE or symptom profile. d) Correlation between peak S1 IgG Ab titre and T cell response to NP protein in HCW with laboratory-confirmed SARS-CoV-2 infection, coloured by symptom group as above. HCW with no T cell response to NP protein are within the blue box.

e) The age in years of HCW for whom a T cell response to NP protein was detected (top) or was not (bottom). is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint

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80+ (ΔSFC)

COVID-19 IP, n, % 6 (5.5) 2 (4) 2 (10)