Shedding of the SARS-CoV-2 in fully vaccinated individuals is for a much shorter duration compared to those who are either partially or unvaccinated, according to a study reported in JAMA Network Open.¹

Researchers from South Korea analysed data of patients with Covid-19 to establish the difference in the transmissibility of SARS-CoV-2 shedding between the fully vaccinated patients (breakthrough infection group) and those who were either partially or unvaccinated (nonbreakthrough infection group).

This study had two arms: a secondary transmission study (cohort 1) and a viral kinetics shedding study (cohort 2). The first group (cohort 1) involved 173 health care workers (HCWs) and hospitalized patients and/or their caregivers who tested positive for Covid-19 during their stay in tertiary care hospital (or residence for caregivers) from 1st March 2020 to 6th November, 2021. The second group (cohort 2) included 45 patients, median age 37 years, with mild delta infection between 20^th July 2021 and 20^th August, 2021.

In the secondary transmission study, nearly 30% (n = 50) had a breakthrough infection. Women comprised 58% of this study group. In this study, the secondary transmission rate was 26% among participants who did not have breakthrough infection (partially or unvaccinated), whereas among those with breakthrough infections (fully vaccinated), the secondary attack rate was just 7%.

In the virus shedding study, around 90% (n=13) of these were either partially or unvaccinated and 13% (n=6) were fully vaccinated. The two groups had similar initial viral load. But on cell culture, the virus remained viable for 8 days after the onset of symptoms among those who had taken only one dose of the vaccine, whereas among the unvaccinated participants, this duration was 10 days from the day of the first symptom. In the fully vaccinated persons, the virus remained viable for just 4 days after symptom onset.

Although the peak viral load in the fully vaccinated persons was initially comparable to that in the unvaccinated people, the duration of shedding of the infectious virus was significantly shorter in them and they also had much lower secondary transmission rate. Therefore, the fully vaccinated individuals were also less likely to spread the infection.

Covid-19 vaccines protect from severe infection, hospitalization and even death. Fully vaccinated persons, especially those who have also taken the booster dose/s, benefit from this protective effect. Even though breakthrough infections may occur, Covid-19 vaccines are still an effective and important means to curb further spread of the infection.

Everyone eligible therefore must complete the vaccination schedule including the precaution dose.

Reference

1. Jung J, et al. Transmission and infectious SARS-CoV-2 shedding kinetics in vaccinated and unvaccinated individuals. JAMA Netw Open. 2022 May 2;5(5):e2213606. doi: 10.1001/jamanetworkopen.2022.13606.