SARS-CoV-2 infection risk among vaccinated and unvaccinated household members during the Alpha variant surge – Denver, Colorado, and San Diego, California, January–April 2021. Issue 33 (5th August 2022)

• Record Type: Journal Article
• Authors: McCormick, David W.; Konkle, Stacey L.; Magleby, Reed; Chakrabarti, Ayan K.; Cherney, Blake; Lindell, Kristine; Namageyo-Funa, Apophia; Visser, Susanna; Soto, Raymond A.; Donnelly, Marisa A.P.; Stringer, Ginger; Austin, Brett; Beatty, Mark E.; Stous, Sarah; Albanese, Bernadette A.; Chu, Victoria T.; Chuey, Meagan; Dietrich, Elizabeth A.; Drobeniuc, Jan; Folster, Jennifer M.; Killerby, Marie E.; Lehman, Jennifer A.; McDonald, Eric C.; Ruffin, Jasmine; Schwartz, Noah G.; Sheldon, Sarah W.; Sleweon, Sadia; Thornburg, Natalie J.; Hughes, Laura J.; Petway, Marla; Tong, Suxiang; Whaley, Melissa J.; Kirking, Hannah L.; Tate, Jacqueline E.; Hsu, Christopher H.; Matanock, Almea;
• Is Part Of: Vaccine. Volume 40:Issue 33(2022)
• Page Start: 4845
• Page End: 4855
• Publication Date: 2022-08-05
• Subjects: CDC US Centers for Disease Control and Prevention -- CI Confidence Interval -- CSTE Council of State and Territorial Epidemiologists -- FDA US Food and Drug Administration -- IR infection risk -- IQR interquartile range -- NP nasopharyngeal -- RBD receptor-binding domain -- RT-PCR reverse transcription polymerase chain reaction -- WGS whole genome sequencing; SARS-CoV-2 -- COVID-19 -- Vaccination -- Vaccine effectiveness -- Household transmission; Vaccines -- Periodicals; 615.372
• DOI: 10.1016/j.vaccine.2022.06.066
• Languages: English
• ISSNs: 0264-410X

Abstract

Highlights: Vaccination reduces the risk household transmission of SARS-CoV-2. Fewer households with a fully vaccinated primary case had secondary cases. The primary SARS-CoV-2 variant in this investigation was the Alpha variant. Vaccinated secondary cases reported fewer symptoms than unvaccinated secondary cases. Abstract: Background: COVID-19 vaccination reduces SARS-CoV-2 infection and transmission. However, evidence is emerging on the degree of protection across variants and in high-transmission settings. To better understand the protection afforded by vaccination specifically in a high-transmission setting, we examined household transmission of SARS-CoV-2 during a period of high community incidence with predominant SARS-CoV-2 B.1.1.7 (Alpha) variant, among vaccinated and unvaccinated contacts. Methods: We conducted a household transmission investigation in San Diego County, California, and Denver, Colorado, during January-April 2021. Households were enrolled if they had at least one person with documented SARS-CoV-2 infection. We collected nasopharyngeal swabs, blood, demographic information, and vaccination history from all consenting household members. We compared infection risks (IRs), RT-PCR cycle threshold values, SARS-CoV-2 culture results, and antibody statuses among vaccinated and unvaccinated household contacts. Results: We enrolled 493 individuals from 138 households. The SARS-CoV-2 variant was identified from 121/138 households (88%). The most common variants were Alpha (75/121, 62%) and Epsilon (19/121, 16%). There were no households with discordant lineages among household members. One fully vaccinated secondary case was symptomatic (13%); the other 5 were asymptomatic (87%). Among unvaccinated secondary cases, 105/108 (97%) were symptomatic. Among 127 households with a single primary case, the IR for household contacts was 45% (146/322; 95% Confidence Interval [CI] 40–51%). The observed IR was higher in unvaccinated (130/257, 49%, 95% CI 45–57%) than fully vaccinated contacts (6/26, 23%, 95% CI 11–42%). A lower proportion of households with a fully vaccinated primary case had secondary cases (1/5, 20%) than households with an unvaccinated primary case (66/108, 62%). Conclusions: Although SARS-CoV-2 infections in vaccinated household contacts were reported in this high transmission setting, full vaccination protected against SARS-CoV-2 infection. These findings further support the protective effect of COVID-19 vaccination and highlight the need for ongoing vaccination among eligible persons.