Vaccination Against SARS-CoV-2 Is Associated With a Lower Viral Load and Likelihood of Systemic Symptoms

Abstract

Background Data conflict on whether vaccination decreases severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) viral load. The objective of this analysis was to compare baseline viral load and symptoms between vaccinated and unvaccinated adults enrolled in a randomized trial of outpatient COVID-19 treatment. Methods Baseline data from the first 433 sequential participants enrolling into the COVID-OUT trial were analyzed. Adults aged 30-85 with a body mass index (BMI) >= 25kg/m 2 were eligible within 3 days of a positive SARS-CoV-2 test and <7 days of symptoms. Log 10 PCR viral loads were normalized to human RNase P by vaccination status, by time from vaccination, and by symptoms. Results 274 participants with known vaccination status contributed optional nasal swabs for viral load measurement: median age 46 years; median BMI 31.2 kg/m 2 (IQR, 27.4, 36.4). Overall, 159 (58%) were women, and 217 (80%) were white. The mean relative log10 viral load for those vaccinated <6 months from date of enrollment was 0.11 (95% CI, -0.48, 0.71), which was significantly lower than the unvaccinated group (p = 0.01). Those vaccinated >= 6 months prior to enrollment did not differ from the unvaccinated with respect to viral load (mean 0.99, 95% CI, -0.41 to 2.40; p = 0.85). The vaccinated group had fewer moderate/severe symptoms of subjective fever, chills, myalgias, nausea, and diarrhea (all P<0.05). Conclusions These data suggest that vaccination within 6 months of infection is associated with a lower viral load, and vaccination was associated with a lower likelihood of having systemic symptoms.

SARS-CoV-2 Secondary Attack Rates in Vaccinated and Unvaccinated Household Contacts during Replacement of Delta with Omicron Variant, Spain

“…These observations are consistent with the reduction of neutralizing antibodies against Omicron observed in experimental studies (20,21) and a notable duration of infectious shedding of the Omicron virus in vaccinated persons (22). The protective effect of vaccination against SARS-CoV-2 infection in the Delta-dominant period was consistent with previous reports on the Delta VOC, which had similar but limited results (6,21,(23)(24)(25)(26). However, we could not ascertain if the booster dose was effective for reducing transmission, likely because of the low sample size (only 46 contacts had booster vaccines administered during the Delta-dominant period).…”

“…However, we could not ascertain if the booster dose was effective for reducing transmission, likely because of the low sample size (only 46 contacts had booster vaccines administered during the Delta-dominant period). The protective effect against the Delta variant diminished as the time since vaccination increased, which has also been previously reported (5,24,26). Our estimates suggest a nonlinear trend for reduction of vaccine protection, culminating at ≈20 weeks after vaccination.…”

At what frequency of vaccination do the vaccinated potentially pose an equal risk to the unvaccinated for transmission of SARS-CoV-2 inside restaurants in New York City?

“…We also assumed that the infectivity of those with SARS-CoV‑2 infection would be similar irrespective of vaccination status. While several studies have found similar viral loads independent of vaccine status [ 7 , 8 ], some studies have found that if vaccinated within 6 months before developing COVID-19, the viral loads might be lower [ 9 ]. Some studies have also suggested that viral loads decrease more rapidly in those who were vaccinated versus those who are unvaccinated [ 5 , 7 ].…”

A collaborative approach to improve representation in viral genomic surveillance

“…One possible explanation for the observed difference in gene copy number/imputed viral load is that during the initial Omicron surge, a greater proportion of the population may have acquired some degree of immunity through vaccination or prior infection. Some reports support the idea of attenuated viral load with vaccination [49][50][51] while others suggest no significant difference between unvaccinated and vaccinated individuals [52][53][54].…”