Data in the UK’s national COVID Infection Survey demonstrate similar vaccine efficacy following a first dose of both PfizerCBioNTech and OxfordCAstraZeneca vaccines . Anti-spike antibody titres are associated with neutralizing activity [, , ], but the degree to which binary or qualitative anti-spike results are a surrogate for protection against infection, or other endpoints of interest such as hospitalization, death, or onward transmission, remains unclear. models to track antibody responses over time. Results 3570/3610 HCWs (98.9%) were seropositive 14?days post first vaccination and prior to second vaccination: 2706/2720 (99.5%) were seropositive after the PfizerCBioNTech and 864/890 (97.1%) following the OxfordCAstraZeneca vaccines. Previously infected and more youthful HCWs were more likely to test seropositive post first vaccination, with no evidence of differences by sex or ethnicity. All 470 HCWs tested 14?days after the second vaccination were seropositive. Quantitative antibody responses were higher after previous contamination: median (IQR)? 21?days post first PfizerCBioNTech 14?604 (7644C22 291) AU/mL versus 1028 (564C1985) AU/mL without prior contamination (p? ?0.001). OxfordCAstraZeneca vaccine recipients experienced lower readings post first dose than PfizerCBioNTech recipients, with and without previous contamination, 10?095 (5354C17 096) and 435 (203C962) AU/mL respectively (both p? ?0.001 versus PfizerCBioNTech). Antibody responses 21?days post second Pfizer vaccination in those not previously infected, 10 058 (6408C15 582) AU/mL, were much like those after prior contamination followed by one vaccine dose. Conclusions SARS-CoV-2 vaccination prospects to detectable anti-spike antibodies in nearly all adult HCWs. Whether differences in response impact vaccine efficacy requires further study. (%); median (IQR). Open in a separate windows Fig.?2 The relationship between vaccine, age and probability of screening anti-spike IgG seropositive 14?days post first vaccination. Model predictions are shown using reference groups for sex and ethnicity (white, female, respectively) and in those without prior evidence of contamination. All 448 HCWs with an antibody test 14?days after their second PfizerCBioNTech vaccine were seropositive. Relatively few HCWs were vaccinated twice with the OxfordCAstraZeneca vaccine, but all 22 assayed 14?days post second dose were seropositive (Supplementary Material Fig.?S3). Quantitative antibody readings before and after vaccination Pre-vaccination quantitative antibody levels were available in 67 previously infected HCWs and 169 without evidence of prior contamination; median (IQR) readings were 334 KU-0063794 (103C1070) and 0.1 (0C1.4) AU/mL respectively. The median (IQR) time from first evidence of previous infection (first positive PCR or serological test) in those previously infected was 31 (0C246) days, with no evidence of association with antibody levels (Spearman’s ?=?C0.09, p 0.45; Supplementary Material Fig.?S4). Quantitative vaccine readings rose during the 3?weeks post first vaccination before plateauing (Fig.?3). Those with previous contamination developed substantially higher titres. In those receiving the PfizerCBioNTech vaccine, the median (IQR) anti-spike IgG reading 21?days post first vaccine dose was 1028 (564C1985) AU/mL without evidence of prior contamination and 14?604 (7644C22 291) AU/mL with (KruskalCWallis p? ?0.001). Those receiving the AstraZeneca vaccine experienced lower titres compared to the PfizerCBioNTech, without and with previous contamination 435 (203C962) AU/mL and 10?095 (5354C17 096) AU/mL KU-0063794 respectively (p? ?0.001 versus PfizerCBioNTech and within AstraZeneca). In previously uninfected HCWs, after PfizerCBioNTech vaccination higher titres were seen in more youthful age groups (Fig.?3C). Normally, there was no obvious relationship between age and post-vaccination antibody readings. Open in a separate windows Fig.?3 Modelled quantitative anti-spike IgG responses following first vaccination by vaccine and previous infection status. Panels A and B show responses in previously infected healthcare workers (HCWs) and panels C and D HCWs without evidence of previous infection. Panels A and C show data for those receiving PfizerCBioNTech vaccine and panels B and D OxfordCAstraZeneca vaccine. Model predictions are shown at three example ages: 30, 45, and 60?years. The shaded ribbon shows the 95% confidence interval. Values KU-0063794 are plotted from 7?days prior to vaccination to illustrate baseline values (models are fitted using data from 28?days prior to vaccination onwards). In HCWs receiving a second PfizerCBioNTech vaccine dose, antibodies were boosted in previously uninfected individuals, with the highest levels in more youthful HCWs, but with some waning of responses from day 20 to 60 post vaccination (Fig.?4). Median (IQR) anti-spike IgG readings 21?days post second vaccine dose were 10?058 (6408C15 582) AU/mL without evidence of previous infection and 18?047 (10?884C22 413) AU/mL with such evidence. Hence, anti-spike readings post second vaccination in those without evidence of KU-0063794 previous contamination (Fig.?4B) were much like those seen after Vezf1 one vaccination in previously infected HCWs (Figs.?3A,B). Open in a separate windows Fig.?4 Modelled quantitative anti-spike IgG titres following second PfizerCBioNTech vaccination by previous infection status. Panel A shows those who were previous infected.