SARS-CoV-2 Delta Variant Breakthrough Infection and Onward Secondary Transmission in Household

Abstract

Background Despite the extraordinary speed of mass vaccination efforts, an outbreak of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) delta variant in a vaccinee with coronavirus disease 2019 (COVID-19) mRNA vaccine was identified in an adult day service center (ADSC) of Jeju, South Korea. The primary objective of this study was to investigate the epidemiologic features in infection-vulnerable facilities with a high vaccination rate of BNT162b2 mRNA COVID-19 vaccine. The second was to estimate the secondary transmission prevention effect of the vaccine in the household members by vaccination status. Methods We included all ADSC participants, staff and their household members. All COVID-19 infected cases were confirmed by reverse transcriptase polymerase chain reaction. We calculated attack rate in ADSC and the secondary attack rate (SAR) in household members by vaccination status. Results Among a total of 42 participants and 16 staff, of which 96.6% were fully vaccinated with BNT162b2 mRNA COVID-19 vaccine, 12 symptomatic cases and 13 asymptomatic confirmed cases of COVID-19 were found. The attack rate was 43.1%, with 13 isolates identified as SARS-CoV-2 virus, delta variant. The SAR in unvaccinated and partially vaccinated household members were 27.8% (5/18) and 25.0% (5/20), respectively, while the SAR in fully vaccinated household members was 12.5% (1/8). Conclusion We describe a SARS-CoV-2 delta variant outbreak in ADSC with high vaccine coverage rate, characterized by high infection rate, high transmissibility, and low clinical severity. The outbreak proceeded to unvaccinated or partially vaccinated household members, emphasizing the need for immunizing close contacts of high-risk groups.

Increased Secondary Attack Rate among Unvaccinated Household Contacts of Coronavirus Disease 2019 Patients with Delta Variant in Japan

“…The HSAR of unvaccinated contacts of the index patient with the Delta variant was 48%. Previous studies reported that HSAR among unvaccinated, or mainly unvaccinated households were 26% in Singapore [ 10 ], 35% in Thailand [ 11 ], 38% and 28% in Korea [ 12 , 13 ], 53% in USA [ 14 ], and 22% for household of unvaccinated index patients in Netherland [ 15 ]. The HSAR in the present study is relatively similar to the previous studies.…”

“…While studies regarding HSAR of COVID-19 due to wild strain have been published in various countries, studies reporting HSAR of Delta SARS-CoV-2 variant remains sparse [ 10 , 11 , 12 , 13 , 14 , 15 ]. HSAR was 26% for Delta variant in Singapore, and 38% for Alpha variant in Denmark [ 10 , 16 ].…”

Vaccination coverage among COVID-19 prevention and control management teams at primary healthcare facilities in China and their attitudes towards COVID-19 vaccine: a cross-sectional online survey

“…Furthermore, those with non-medical titles had nearly twice the chance of giving a higher score of uncertainty of vaccine safety and vaccine efficacy compared with those with junior medical titles. According to the report by Ming-Wei Wang et al, 22 the HCWs have a higher vaccination rate and are less hesitant or reluctant on COVID-19 vaccine than non-HCW 10. All of the evidence above would indirectly suggest that promotion of COVID-19 vaccination programme in public would be a challenge due to the lack of general medical education.…”

Evaluating efficacy of indoor non-pharmaceutical interventions against COVID-19 outbreaks with a coupled spatial-SIR agent-based simulation framework

“…SAR is especially useful for quantifying household infectivness as it considers contacts that occur among individuals within close confines, and is applicable to our study, where individuals spend most of their workday in the same shared space. Assuming SAR to be a good approximation of in our model, we use empirically estimated 95% confidence intervals of mean SAR for four respiratory diseases from the literature to define ranges of as follows, MERS: [0.009, 0.107] 37 , SARS [0.048, 0.107] 37 , Measles [0.520, 0.846] 37 , earlier variants of COVID-19: [0.14, 0.22] 38 , 39 , and the more contagious Delta variant: [0.20, 0.32] among unvaccinated individuals 38 – 40 . At the time of writing, there was no peer-reviewed study estimating the SAR of the COVID-19 Omicron variant to our knowledge that would could include in our analysis.…”