key: cord-0917801-61sg7k5c authors: Hsu, Lea; Hurraß, Julia; Kossow, Annelene; Klobucnik, Jan; Nießen, Johannes; Wiesmüller, Gerhard A.; Grüne, Barbara; Joisten, Christine title: Breakthrough infections with the SARS-CoV-2 Delta variant: Vaccinations halved transmission risk date: 2022-01-11 journal: Public Health DOI: 10.1016/j.puhe.2022.01.005 sha: 8103f4364abeab4a45037376b2085801a44669cb doc_id: 917801 cord_uid: 61sg7k5c Objectives The SARS-CoV-2 Delta variant (B.1.617.2) is associated with increased infectivity. Data on breakthrough SARS-CoV-2 Delta variant infections in vaccinated individuals and transmission risk are limited. The aim of this study was to provide estimates of transmission risk in Delta variant breakthrough infections. Study design : Methods To analyse onward transmission of fully vaccinated individuals infected with B.1.617.2, we compared 85 patients (vaccination group [VG]) with an age- and sex-matched unvaccinated control group (CG; n = 85). Results Transmission of B.1.617.2 was significantly reduced (halved) in the VG. The number of infected contacts to total number of contacts per infected person was 0.26 ± 0.40 in the VG vs 0.56 ± 0.45 in the CG (p = .001). Similarly, fully vaccinated contacts were less likely to be infected by fully vaccinated infected persons (IPs) than by unvaccinated IPs (20.0% vs 37.5%), although this association was not significant. Conclusions Fully vaccinated contacts had 50% less transmissions than unvaccinated individuals. These findings must be verified in larger sample populations and it is especially important to investigate the role of vaccination status of close contacts. The SARS-CoV-2 delta (B.1.617.2) variant of concern (VoC) has rapidly become the dominant variant in numerous countries and now accounts for over 95% of cases in Germany. 1 It was first reported in India in early October 2020 and increasingly displaced other SARS-CoV-2 variants, such as Alpha (B.1.1.7), Beta (B.1.351) and Gamma (P.1). In addition to other authors, Liu et al. 2 identified the spike mutation P681R as a significant determinant for enhanced viral replication fitness of the Delta variant compared with the Alpha variant. Thus, the R0 (the initial reproduction number in an immune-naïve population) of the ancestral COVID-19 strain (wild type), the Alpha variant and the Delta variant, was reported as 2.4-2.6, 4-5 and 5-8, respectively. 3 Initial data show that (full) vaccination protects against infection with the Delta variant, but vaccine effectiveness seems to be reduced. 4 However, it is unclear whether complete vaccination influences onward transmission in the case of so-called breakthrough infections. Preliminary results found no difference in viral load between unvaccinated and vaccinated individuals with breakthrough infections. 5 In contrast, Chia et al. demonstrated that the viral load of B.1.617.2 decreased more rapidly in vaccinated than in unvaccinated infected individuals (preliminary data). 6 In terms of breakthrough B.1.617.2 infections following AstraZeneca vaccination, Chau et al. described asymptomatic or mild diseases, which were associated with higher cycle threshold (Ct) values, prolonged polymerase chain reaction (PCR) positivity and low levels of vaccine-induced neutralising antibodies. 7 However, the effect of vaccination is not only via neutralising antibodies, but also cellular immunity. Thus, a robust T-cell response also correlates with clinical protection and is probably involved in immunity to COVID-19 even with a reduction in antibodies. 8 Accurate assessment of breakthrough infections and the risk of ongoing transmission from vaccinated contact with an infected person (IP) for >10 minutes at <1.5 m, without face masks or direct physical contact, within a timeframe ranging from 2 days before symptom onset in the IP to 10-14 days after symptom onset. 9 To analyse vaccine-induced protection in terms of Delta variant breakthrough infections, real-world data from the largest German public health department, which is based in Cologne, were used. Data for transmission of B.1.617.2 infection to close contacts was compared between fully vaccinated IPs in the vaccination group (VG) and IPs in the unvaccinated control group (CG). We considered the total number of contacts per IP and the total number of infected contacts per IP to determine the infected contacts relative to the total number of contacts per IP. In addition to descriptive statistics (age and sex), differences between VG and CG were assessed using an unpaired t-test and a chi-squared test, respectively. Linear regression (backwards elimination) was used to examine the influence of vaccination (yes = 0, no = 1), age (in years), sex (male = 1, female = 2), symptoms (present = 1, not present = 2) and vaccination interval (in days) on the number of infected contacts relative to the total number of contacts per IP. A p-value below .05 was considered significant. All calculations were performed with SPSS version 27.0. In both the VG and CG, 45.9% were female. On average, vaccinated individuals were 35.8 +/-17.7 years old; this did not differ from the CG (age: 34.8 +/-16.0 years). In the VG group, 138 close contacts (range per IP 0-9) were identified, compared with 95 close contacts in the CG (range per IP 0-7). The number of total and infected contacts, as well as the number of infected contacts in relation to the total number of contacts per IP, are shown in Table 1 . There was a trend towards a higher number of total contacts per IP in the VG, but these contacts were significantly less infected. The total number of Based on real-world studies, SARS-CoV-2 vaccines have reassuring safety and can effectively reduce fatal outcomes, severe cases, symptomatic cases and infections. 10 In addition, a follow-up of 6 months after the application of BNT162b2 showed a favourable safety profile, but with a gradual decline in efficacy. 11 Similarly, fully vaccinated contacts were less likely to be infected by fully vaccinated infected persons (IPs) than by unvaccinated IPs (20.0% vs 37.5%), although this association was not significant. A strength of this study is the systematic and complete recording of the data by the Cologne Public Health Department. IPs were digitally recorded and interviewed via telephone to determine the route of infection, symptoms and medical history, including vaccination. In each case, VoC analysis was carried out via PCR, provided that sufficient sample material was available. Accordingly, the proportion of B1.617.2 infections was complete compared with other surveys, which often assume estimated values. Additionally, all close contacts in Cologne were also tracked during quarantine, both digitally and by telephone. PCR testing is carried out when symptoms occur. This study is limited by its small number of IPs and fully vaccinated close contacts. Additionally, deviations in PCR tests and sequencing in various Cologne laboratories are possible because a unified method is not present. Although the ct values were recorded, they were only available at one test time in IPs; therefore, ct values were not taken into account in the context of this analysis. In conclusion, fully vaccinated individuals who are infected with B.1.617.2 can transmit the infection to close contacts; however, they had a greater than 50% reduced transmission rate compared with the unvaccinated CG. These findings must now be verified in larger sample populations. It will be especially important to investigate the role of vaccination status of close contacts and to also consider the decreased efficacy of the vaccine over time. Table 1 Total contacts, total infected contacts and relation to the total number per infected persons (IPs); total fully vaccinated contacts and infected fully vaccinated contacts in total and in relation to total number in vaccination group (VG) vs control group (CG) *Calculated with unpaired t-test. ** persons who did not indicate close contacts were also integrated in order not to distort the number. ***only taken into account if close contacts were indicated. 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Safety and Efficacy of the BNT162b2 mRNA Covid-19 Vaccine through 6 Months Initial report of decreased SARS-CoV-2 viral load after inoculation with the BNT162b2 vaccine Single dose of a mRNA SARS-CoV-2 vaccine is associated with lower nasopharyngeal viral load among nursing home residents with asymptomatic COVID-19 Transmission of SARS-CoV-2 variant B.1.1.7 among vaccinated health care workers We want to thank all members of the contact tracing team at the Cologne Public Health Department. Due to the retrospective nature of the analyses and use of anonymised data listings, ethical committee approval was not required.