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Recent COVID-19 Vaccination and Risk of SARS-CoV-2 Transmission
These are the results of a prospective, case-ascertained household transmission study in which the first household member with confirmed SARS-CoV-2 infection (primary case participant) was identified through outpatient settings and enrolled with their household contacts from January 1, 2024, to January 31, 2025. COVID-19 vaccination history was verified by study staff. Participants collected daily nasal swabs for 10 days regardless of symptoms. Swabs were tested for SARS-CoV-2 via reverse transcription–polymerase chain reaction. Household contacts were considered infected if at least one swab tested positive for SARS-CoV-2. Secondary infection risk was calculated as the number of infected contacts divided by the total number of contacts. In this study of 362 primary case participants with SARS-CoV-2 infection and their 763 household contacts, 62% of household contacts were infected with SARS-CoV-2. Household contacts of primary case participants vaccinated six months or less before onset had nearly one-half the infection risk compared with contacts of unvaccinated primary case participants. These findings suggest that COVID-19 vaccination may have an indirect benefit of decreasing transmission and thus reducing overall exposure to SARS-CoV-2.
Early-Phase Oral Antiviral Use and Post–COVID-19 Condition in Outpatients
This prospective, nationwide, multicenter, registry-based cohort study was conducted at 51 acute-care hospitals across Japan during the predominance of Omicron sublineages JN.1 and KP.3. Outpatients aged 12 years or older with laboratory-confirmed COVID-19, symptom onset of five days or less before enrollment, and no recent anti–SARS-CoV-2 treatment were enrolled between February and October 2024, with follow-up through February 2025. The primary analysis population included participants with complete baseline covariates and valid day 28 and day 84 assessments. In this cohort study including 7,699 outpatients, early oral antiviral use was associated with a significantly lower risk of post-COVID-19 condition (PCC) in the primary adjusted analysis. Participants receiving antivirals were less likely to fail to return to usual health by day 84. These findings suggest that early oral antiviral use may help reduce the risk of PCC and support recovery in outpatients with COVID-19.
Impact of Early Oral Antiviral Use for Outpatients With COVID-19 on Healthcare Utilization and Recovery (ANCHOR-02)
These are results from a nationwide, multi-institutional (51 acute-care hospitals in Japan), prospective, registry-based cohort study enrolled outpatients aged ≥12 years with laboratory-confirmed COVID-19 within 5 days of symptom onset (February 1–October 31, 2024). Participants were compared between those with and without oral antiviral use at enrollment (ensitrelvir, nirmatrelvir, or molnupiravir) for medical re-consultation, failure to return to usual health, and work productivity and activity impairment through Day 28. Baseline characteristics were generally comparable between groups (efficacy analysis population: antiviral n=2,271; no antiviral n=5,768). Overall re-consultation rates tended to be lower in the antiviral group (adjusted risk ratio [aRR] 0.93; 95% CI 0.83-1.04). Antiviral use was associated with lower rates of failure to return to usual health (aRR 0.76; 95% CI 0.70-0.82) and with improvements in presenteeism, overall work impairment, and activity impairment.
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