Comparison of the Risk of Hospitalization and Severe Disease Among Co-circulating Severe Acute Respiratory Syndrome Coronavirus 2 Variants.

BACKGROUND: We compare the risk of coronavirus disease 2019 (COVID-19) outcomes among co-circulating severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants between January 2021 and May 2022 in Navarra, Spain. METHODS: We compared the frequency of hospitalization and severe disease (intensive care unit admission or death) due to COVID-19 among the co-circulating variants. Variants analyzed were nonvariants of concern (non-VOCs), Alpha, Delta, Omicron BA.1, and Omicron BA.2. Logistic regression models were used to estimate adjusted odds ratio (aOR). RESULTS: The Alpha variant had a higher risk of hospitalization (aOR, 1.86 [95 confidence interval {CI}, 1.282.71]) and severe disease (aOR, 2.40 [95 CI, 1.314.40]) than non-VOCs. The Delta variant did not show a significantly different risk of hospitalization (aOR, 0.73 [95 CI, .401.30]) and severe disease (aOR, 3.04 [95 CI, .5716.22]) compared to the Alpha variant. The Omicron BA.1 significantly reduced both risks relative to the Delta variant (aORs, 0.28 [95 CI, .16.47] and 0.23 [95 CI, .12.46], respectively). The Omicron BA.2 reduced the risk of hospitalization compared to BA.1 (aOR, 0.52 [95 CI, .29.95]). CONCLUSIONS: The Alpha and Delta variants showed an increased risk of hospitalization and severe disease, which decreased considerably with the Omicron BA.1 and BA.2. Surveillance of variants can lead to important differences in severity.

Differences in Transmission between SARS-CoV-2 Alpha (B.1.1.7) and Delta (B.1.617.2) Variants.

The present study aimed to compare the susceptibility and infectivity between the Alpha and Delta variants of SARS-CoV-2 and to investigate characteristics of the index case and the contact that may affect transmission. The risk of SARS-CoV-2 infection was compared between close contacts of COVID-19 cases with Alpha and Delta variants during June 2021 to August 2021. In index cases, Spike gene target failure (TaqPath) was used as a proxy of Alpha variant and the L452R mutation (TaqMan) for Delta variant. Cox regression models were used to estimate adjusted relative risks (RR). We compared close contacts of index cases with Alpha (n = 2139) and Delta variants (n = 5439). Delta variant was more transmissible overall (relative risk [RR] 1.32, 95% CI = 1.13 to 1.53), and in non-household contacts (RR 1.71, 95% CI = 1.35 to 2.16), but not in household contacts (RR 1.10, 95% CI = 0.91 to 1.34; Pinteraction < 0.001). Delta variant excess transmission was observed when the index cases were 12 to 39 years old (RR 1.51, 95% CI = 1.27 to 1.79) and the close contacts were 18 to 39 years old (RR 1.62, 95% CI = 1.29 to 2.03), but not among those younger or older than such ages. Differences in transmissibility between variants disappeared with vaccination of the index case (RR 0.68, 95% CI = 0.46 to 1.02), but not with vaccination of the close contact. This report shows that the Delta variant is more transmissible than Alpha variant mainly among young adults. Vaccination of the index cases reduced the excess transmission, which reinforces the recommendation of vaccination to reduce transmission of the Delta variant. IMPORTANCE The higher transmissibility of the Delta variant of SARS-CoV-2 in comparison with the Alpha variant has been reported. We compared the transmission of the Alpha and Delta variants by characteristics and COVID-19 vaccination status of index cases and their close contacts. Interestingly, the Delta variant showed increased transmissibility when the index case was an adolescent or young adult and when the close contact was a young adult; however, in index cases and close contacts of other age groups, transmission did not differ between variants. This may explain the increased proportion of young people who have been infected in the surges due to the Delta variant. The Delta variant was more transmissible than the Alpha variant when the index cases were unvaccinated against COVID-19, and their vaccination equaled the transmissibility of both variants, which suggests a higher impact of vaccination in controlling transmission of the Delta variant.

Risk Factors of Infection, Hospitalization and Death from SARS-CoV-2: A Population-Based Cohort Study.

We conducted a prospective population-based cohort study to assess risk factors for infection, hospitalization, and death from SARS-CoV-2. The study comprised the people covered by the Health Service of Navarre, Spain. Sociodemographic variables and chronic conditions were obtained from electronic healthcare databases. Confirmed infections, hospitalizations, and deaths from SARS-CoV-2 were obtained from the enhanced epidemiological surveillance during the second SARS-CoV-2 epidemic surge (July-December 2020), in which diagnostic tests were widely available. Among 643,757 people, 5497 confirmed infections, 323 hospitalizations, 38 intensive care unit admissions, and 72 deaths from SARS-CoV-2 per 100,000 inhabitants were observed. A higher incidence of confirmed infection was associated with people aged 15-29 years, nursing home residents, healthcare workers, people born in Latin America or Africa, as well as in those diagnosed with diabetes, cardiovascular disease, chronic obstructive pulmonary disease (COPD), chronic kidney disease, dementia, severe obesity, hypertension and functional dependence. The risk of hospitalization in the population was associated with males, higher age, nursing home residents, Latin American or African origin, and those diagnosed with immunodeficiency, diabetes, cardiovascular disease, COPD, asthma, kidney disease, cerebrovascular disease, cirrhosis, dementia, severe obesity, hypertension and functional dependence. The risk of death was associated with males, higher age, nursing home residents, Latin American origin, low income level, immunodeficiency, diabetes, cardiovascular disease, COPD, kidney disease, dementia, and functional dependence. This study supports the prioritization of the older population, nursing home residents, and people with chronic conditions and functional dependence for SARS-CoV-2 prevention and vaccination, and highlights the need for additional preventive support for immigrants.