A study has suggested that among unvaccinated individuals, infection with the delta COVID-19 variant doubles the risk of hospitalisation.
The emergence of COVID-19 variants, in particular the delta COVID-19 variant, is a cause for concern, especially, given evidence of reduced effectiveness of vaccines against the variant. Nevertheless, despite this, other data has indicated that vaccination protects against hospitalisation in those infected with the delta variant.
In an attempt to better characterise the severity of infection caused by the delta COVID-19 variant, a team from Public Health England, examined the relative risk of both hospital emergency care attendance or admission following infection with the variant and the extent to which this was modified by vaccination. The team used individual-level data on those with laboratory-confirmed COVID-19 infection between March 29 and May 23, 2021 and with whole viral genomic sequencing of either the alpha or delta COVID-19 variants. The risk of hospital admission and attendance at emergency care were compared for patients with either variant and by vaccination status, over a maximum of 14 days from their positive COVID-19 test. The primary analysis was the risk of hospitalisation outcomes (i.e., either admission or attendance), based on hazard ratios (HR). The main secondary analysis was the HRs for the same hospital outcomes based on vaccination status, which was dichotomised as either unvaccinated or less than 21 days since the first vaccine dose or 21 or more days since the first dose. Results were adjusted for age, sex, area of residence (based on deprivation) and the presence of any international travel within 14 days of a positive test.
Over the period of the study, there were 43,338 cases included in the analysis with 8,682 infections with the delta COVID-19 variant and 34,656 with the alpha variant. In addition, the majority of patients in both groups (74%) were unvaccinated. The median age of those infected with the delta COVID-19 variant was 29 years (48.9% female) which was slightly lower than those with the alpha variant (median age 31 years, 51.7% female). The estimated risk for hospitalisation within 14 days was higher with the delta COVID-19 variant compared with the alpha variant (adjusted HR, aHR = 2.26, 95% CI 1.32 – 3.89). Similarly, there was an increased risk for hospital admission or emergency care attendance within 14 days of infection for the delta compared with the alpha variant (aHR = 1.45, 95% CI 1.08 – 1.95).
When the data were analysed in terms of vaccination status, among those who were either unvaccinated or who had been vaccinated less than 21 days before infection, the risk of hospital admission was also higher among individuals with the delta COVID-19 variant (aHR = 2.32, 95% CI 1.29 – 4.16) and in those 21 days after their first vaccine dose although there was less precision over this outcome due to the wide confidence intervals (aHR = 1.94, 95% CI 0.47 – 8.05). This increased risk was also evident for the combination of hospital admission or emergency care attendance (aHR = 1.58, 95% CI 0.69 – 3.61).
In discussing their findings, the authors recognised that their estimates of the impact of vaccination was imprecise and that further work was needed to confirm the impact of vaccination on breakthrough infections. They concluded that among unvaccinated individuals, infection with the delta COVID-19 variant, doubles the risk of hospital admission.
Twohig KA et al. Hospital admission and emergency care attendance risk for SARS-CoV-2 delta (B.1.617.2) compared with alpha (B.1.1.7) variants of concern: a cohort study. Lancet Infect Dis 2021.