SECONDARY INFECTIONS IN THE FAMILY FROM PRIMARY CASES OF COVID-19 BREAKTHROUGH INFECTIONS IN FULLY VACCINATED OR NOT FULLY VACCINATED PEOPLE. TWO DOSES MODESTLY REDUCE FAMILY TRANSMISSION BUT DOES NOT ELIMINATE IT.

Abstract

Background It is unclear whether vaccination of individuals against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) protects members of their households. Objective Epidemiological evaluation of SARS-CoV-2 transmissibility from fully and incompletely vaccinated index cases with COVID-19 breakthrough infection to initially uninfected family members (secondary attack rate) Methodology An observational, longitudinal, and prospective study of all families with a primary case of COVID-19 breakthrough infection in fully vaccinated or not fully vaccinated people and at least one COVID-19 secondary case in family members was conducted from February to November 2021 in a general medicine office in Toledo, Spain. Clinical and epidemiological variables were compared between secondary cases of primary cases of COVID-19 breakthrough infection in fully vaccinated people versus secondary cases of primary cases of COVID-19 breakthrough infection in not fully vaccinated people. Results Twenty-five index cases (25 families; 84 people) were included, 13 fully vaccinated, which gave rise to 20 secondary cases, and 12 not fully vaccinated, which gave rise to 21 secondary cases. The secondary attack rate of exposed family members to fully vaccinated primary cases were 61% (20/33), and the secondary attack rate of exposed family members to not fully vaccinated primaries was 81% (21/33).  Conclusions In the context of general medicine in Toledo (Spain), from February to November 2021 (before omicron), two doses of COVID-19 vaccine vs. only one modestly reduce family transmission but do not eliminate it.