LAUSR

SARS-CoV-2 vaccines administered in the UK are highly effective in preventing hospitalisation and death from COVID-19 [1]. Patients with immunocompromise are less likely to be able to mount a satisfactory immunological response to the vaccine and therefore may remain at higher risk of moderate-to-severe COVID-19 [2]. Understanding the reasons and risk-factors for admission will provide insight into strategies for future vaccination. This study aimed to characterise the hospitalised vaccinated population and identify the effect of the relationship between vaccination status and immunocompetence on hospital mortality using the prospective observational cohort recruited from the UK Coronavirus Clinical InformationNetwork (CO-CIN). ISARIC4C/CO-CIN collected data on hospitalised patients with COVID-19 in the UK since February 2020 [3]. The National Immunisation Management Service contains vaccine type and date of first and/or second vaccination since the COVID-19 vaccination programme started in the UK on 8 December 2020. We linked data in CO-CIN and the National Immunisation Management Service and restricted our population to adults admitted to hospital with symptomatic polymerase chain reaction (PCR)-positive SARS-CoV-2 infection with at least 28 days of follow-up. This is a complete case analysis. Patients with re-infection were removed from this analysis. We categorised patients into the following three groups: no virus immunity – unvaccinated patients and patients experiencing symptoms ≤ 20 days after first vaccination dose [4]; first dose failure – patients experiencing symptoms ≥ 21 days after first vaccination dose or patients experiencing symptoms ≤ 13 days after second vaccination dose; and second dose failure – patients experiencing symptoms ≥ 14 days after second vaccination dose. Immunocompromise was defined as pre-existing immunological or metabolic disorder (e.g. severe combined immunodeficiency or common variable immunodeficiency); solid organ transplant; HIV/AIDS; cancer on active treatment with chemotherapy or immune modifying drugs; or receipt of immunosuppressing drugs. We assessed the association between immunocompromise, vaccine failure status and 28-day mortality, adjusting for age, sex, ethnicity, socio-economic status and comorbidity using logistic regression with an interaction between immunocompromise and vaccine failure status. There were 40,870 patients recruited to ISARIC4C/COCIN between 8 December 2020 and 15 August 2021 with symptomatic PCR-positive COVID-19. At the time of admission, 33,856 (82.8%) patients were unvaccinated; 5332 (13.0%) had received their first vaccination; and 1682 (4.1%) had received their second vaccination. Of the 7014 patients who had received a vaccination, 3606 (51.4%) had no virus immunity; 1941 (27.7%) had first dose failure; and 1467 (20.9%) had second dose failure (see online Supporting Information Figure S1), proportions which persistedwhen restricting to patients with at least 60 days of follow-up (see online Supporting Information Figure S2). Despite lower absolute values, the relative proportion of immunocompromised patients increased from no virus immunity (12.4%) to first dose failure (17.5%) to second dose failure (20.6%) (Table 1). After adjustment, vaccination reduced the odds of mortality in patients admitted to hospital (Fig. 1 and online Supporting Information Figure S3). Immunocompromised patients had consistently higher odds of mortality compared with immunocompetent patients (Fig. 1), and there was a significant interaction between vaccination status and immunocompromise (p = 0.001). Most patients hospitalised with symptomatic COVID-19 since the vaccination programme began in the UK have not been vaccinated, and for those who have received a vaccine, most admissions occurred within 3 weeks of the first dose before the vaccine would be expected to be effective (see online Supporting Information Figure S1). It is important to highlight to the general population that there is a lag between receiving a vaccination and developing the immunity required to prevent hospitalisation or death, as awareness may alter postvaccination behaviour. We found that vaccination generally