Immune escape and waning immunity of COVID-19 monovalent mRNA vaccines against symptomatic infection with BA.1/BA.2 and BA.5 in Japan.

Background: Repeated emergence of variants with immune escape capacity and waning immunity from vaccination are major concerns for COVID-19. We examined whether the surge in Omicron subvariant BA.5 cases was due to immune escape or waning immunity through vaccine effectiveness (VE) evaluation.

Effectiveness of BA.1- and BA.4/BA. 5-Containing Bivalent COVID-19 mRNA Vaccines Against Symptomatic SARS-CoV-2 Infection During the BA.5-Dominant Period in Japan.

In this multicenter, prospective, test-negative, case-control study in Japan, the effectiveness of both BA.1-containing and BA.4/BA.

Coronavirus Disease 19 (COVID-19) Vaccine Effectiveness Against Symptomatic Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Infection During Delta-Dominant and Omicron-Dominant Periods in Japan: A Multicenter Prospective Case-control Study (Factors Associated with SARS-CoV-2 Infection and the Effectiveness of COVID-19 Vaccines Study).

Background: Although several coronavirus disease 2019 (COVID-19) vaccines initially showed high efficacy, there have been concerns because of waning immunity and the emergence of variants with immune escape capacity.

Methods: A test-negative design case-control study was conducted in 16 healthcare facilities in Japan during the Delta-dominant period (August-September 2021) and the Omicron-dominant period (January-March 2022). Vaccine effectiveness (VE) against symptomatic severe acute respiratory syndrome coronavirus 2 infection was calculated for 2 doses for the Delta-dominant period and 2 or 3 doses for the Omicron-dominant period compared with unvaccinated individuals.

Social and Behavioral Factors Associated with Lack of Intent to Receive COVID-19 Vaccine, Japan.

Persons in Japan who did not intend to receive COVID-19 vaccines after widespread rollout were less likely than others to engage in preventive measures or to be afraid of getting infected or infecting others. They were also not less likely to engage in potentially high-risk behaviors, suggesting similar or higher exposure risks.

Behavioral factors associated with SARS-CoV-2 infection in Japan.

Background: The relative burden of COVID-19 has been less severe in Japan. One reason for this may be the uniquely strict restrictions imposed upon bars/restaurants. To assess if this approach was appropriately targeting high-risk individuals, we examined behavioral factors associated with SARS-CoV-2 infection in the community.