A pre-print study by Nguyen Van Vinh Chau et al titled “Transmission of SARS-CoV-2 Delta variant among vaccinated healthcare workers, Vietnam” has found that vaccinated individuals who were infected had 251 times the viral load compared to those infected in 2020.
The study reports that one hospital staff member tested positive on 11 June 2021. In the following days, 683 staff members were tested. In total, 69 tested positive (and 62 participated in the study). They have been vaccinated with the Astrazeneca vaccine during March and April 2021.
The viral loads of the 49 (pre)symptomatic cases peaked within 2-3 days before and after symptom onset, with a median Ct value (range) of 16.8 (13.1–36.9), corresponding to log10 copies per mL of 9.1 (range: 2.8–10.2) (Figure 2A). During the course of infection, peaks of viral loads measured at any time point of the symptomatic cases were higher than that of asymptomatic cases; 16.5 (13.6–32) vs. 30.8 (13.1–36.9), equivalent to median log10 viral load of 9.2 copies per mL (range: 4.3–10.1) vs. 4.7 copies per mL (range: 2.8–10.2), p=0.005, respectively (Supplementary Figure 2). The median time from diagnosis to PCR negative prior discharge was 21 days (range: 8–33).
Compared with peak viral loads of cases infected with old SARS-CoV-2 strains detected in Vietnam between March and April 2020, peak viral loads of breakthrough cases were significantly higher, median log10 viral load in copies per mL (range): 9.1 (range: 2.8–216 10.2) vs. 6.7 (1.9–9.5), equivalent to 251 times higher for median viral loads. The differences were more profound among symptomatic cases while there was no difference in viral loads among asymptomatic cases between the two groups (Figure 2B).
It should be noted that 10 of the individuals had data regarding their neutralizing antibody levels at two weeks after their second vaccine dose and at diagnosis, and in both these points in time had lower levels than the uninfected controls. So, for these 10 individuals, maybe their immunity is inherently not as good as the others.
In any case, vaccinated individuals getting infected anyway is not all that surprising if the vaccine doesn’t work properly. But at such higher viral loads than previously measured for what is supposed to be the same virus (even if it is a different variant), one has to wonder whether these vaccines are facilitating the spread. Well, that’s not that surprising either… some doctors predicted as much.
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