Effectiveness of ChAdOx1-S COVID-19 booster vaccination against the Omicron and Delta variants in England.

Despite the availability of the ChAdOx1-S booster vaccine, little is known about the real-world effectiveness although clinical trials have demonstrated enhanced immunity following a ChAdOx1-S booster. In England 43,171 individuals received a ChAdOx1-S booster whilst 13,038,908 individuals received BNT162b2 in the same period. ChAdOx1-S booster recipients were more likely to be female (adjusted odds ratio (OR) 1.67 (1.64-1.71)), in a clinical risk group (adjusted OR 1.58 (1.54-1.63)), in the clinically extremely vulnerable group (adjusted OR 1.84 (1.79-1.89)) or severely immunosuppressed (adjusted OR 2.05 (1.96-2.13)). The effectiveness of the ChAdOx1-S and BNT162b2 boosters is estimated here using a test-negative case-control study. Protection against symptomatic disease with the Omicron variant peaks at 66.1% (16.6 to 86.3%) and 68.5% (65.7 to 71.2%) for the ChAdOx1-S and BNT162b2 boosters in older adults. Protection against hospitalisation peaks at 82.3% (64.2 to 91.3%) and 90.9% (88.7 to 92.7%). For Delta, effectiveness against hospitalisation is 80.9% (15.6% to 95.7%) and 93.9% (92.8% to 94.9%) after ChAdOx1-S and BNT162b2 booster vaccination. This study supports the consideration of ChAdOx1-S booster vaccination for protection against severe COVID-19 in settings yet to offer boosters and suggests that individuals who received a ChAdOx1-S booster do not require re-vaccination ahead of others.

Effectiveness of COVID-19 booster vaccines against COVID-19-related symptoms, hospitalization and death in England.

Booster vaccination with messenger RNA (mRNA) vaccines has been offered to adults in England starting on 14 September 2021. We used a test-negative case-control design to estimate the relative effectiveness of a booster dose of BNT162b2 (Pfizer-BioNTech) compared to only a two-dose primary course (at least 175 days after the second dose) or unvaccinated individuals from 13 September 2021 to 5 December 2021, when Delta variant was dominant in circulation. Outcomes were symptomatic coronavirus disease 2019 (COVID-19) and hospitalization. The relative effectiveness against symptomatic disease 14-34 days after a BNT162b2 or mRNA-1273 (Moderna) booster after a ChAdOx1-S (AstraZeneca) and BNT162b2 as a primary course ranged from around 85% to 95%. Absolute vaccine effectiveness ranged from 94% to 97% and was similar in all age groups. Limited waning was seen 10 or more weeks after the booster. Against hospitalization or death, absolute effectiveness of a BNT162b2 booster ranged from around 97% to 99% in all age groups irrespective of the primary course, with no evidence of waning up to 10 weeks. This study provides real-world evidence of substantially increased protection from the booster vaccine dose against mild and severe disease irrespective of the primary course.

Disease severity during SARS-COV-2 reinfection: a nationwide study.

OBJECTIVE: We aimed to look at the burden of disease caused by SARS-COV-2 reinfections and identified potential risk factors for disease severity. METHODS: We used national surveillance data to collect information on all SARS-CoV-2 primary infection and suspected reinfection cases between January 2020 until early May 2021. Reinfection cases were positive COVID-19 PCR or antigen test, 90 days after their first COVID-19 positive test. We collected information on case demographics, hospital and ICU admission, immunisation status and if individuals were at risk of complication for COVID-19. RESULTS: Deaths reported within 28 days of testing positive were 61% (95% confidence interval: 56% to 65%) lower in suspected COVID-19 reinfection than primary infection cases. In the unvaccinated cohort, reinfections were associated with 49% (37% to 58%) lower odds of hospital admission in cases aged 50 to 65 years in the population not identified at risk of complication for COVID-19, and 34% (17% to 48%) in those at risk. ICU admission at reinfection compared to primary infection decreased 76% (55% to 87%). Individuals at risk and those aged below 50 years, who received at least 1 dose of vaccine against COVID-19, were 62% (39% to 74%) and 58% (24% to 77%) less likely to get admitted to hospital at reinfection, respectively. CONCLUSION: Prior SARS-CoV-2 infection was associated with lower odds of dying, and both prior infection and immunisation showed a protective effect against severe disease in selected populations. Older age, sex and underlying comorbidities appeared as principal risk factors for illness severity at reinfection. FUNDING: PHE/UKHSA.