Similar viral load in vaccinated and non-vaccinated individuals infected with the SARS-CoV-2 delta variant

The causative agent of the 2019 coronavirus disease (COVID-19) pandemic, severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is a highly virulent single-stranded RNA virus. Some COVID-19 vaccines have received Emergency Use Authorization (EUA) from several global regulators, and vaccination programs have since been launched in many countries.

study: There is no significant difference in viral load between vaccinated and non-vaccinated, asymptomatic and symptomatic groups infected with the SARS-CoV-2 delta variant... Image Credit: Kirill Kamionskiy / Shutterstock

Scientists say vaccination reduces the mortality and severity of diseases caused by SARS-CoV-2. However, with the advent of SARS-CoV-2 mutants, breakthrough cases are currently being reported. Some mutants can circumvent the immune protection induced by vaccination or natural infection.

To date, all vaccines available are Spike protein Of the original SARS-CoV-2 strain. Avoiding an immune response with SARS-CoV-2 mutants, especially delta mutants, casts doubt on the effectiveness of the COVID-19 vaccine available.

Are vaccinated individuals protected from the SARS-CoV-2 mutant of concern?

Many studies have shown that there is no difference in cycle threshold (Ct value) between vaccinated and unvaccinated individuals.However, others contradicted these results and argued that breakthrough infections showed lower levels, especially among asymptomatic individuals. Viral load From an unvaccinated individual. Health authorities and policy makers need solid evidence to develop effective epidemic control strategies and provide guidelines for containing the ongoing COVID-19 pandemic.

Researchers evaluated Ct values ​​between different groups: a) fully vaccinated and unvaccinated individuals, and b) asymptomatic and symptomatic individuals at the time of testing. During the study period, the delta mutant circulated primarily between two different populations. These are the Unidos en Salud (UeS) community-based site in San Francisco’s mission district and the Healthy Yorotogather (HYT) asymptomatic test by the University of California, Davis.

The preprinted version of the study medRxiv* Server while the article is being peer reviewed.

Main survey results

In this study, a total of 869 samples were analyzed, 500 from the HYT group and 369 from the UeS. All samples belonging to HYT were asymptomatic at the time of sample collection, and researchers found that 75% of COVID-19-positive samples came from unvaccinated individuals.

For the UeS group, COVID-19 positive samples belonged to both symptomatic and asymptomatic individuals. Researchers have found that the UeS group has a higher frequency of vaccine breakthroughs than the HYT group. As expected, the SARS-CoV-2 delta mutant was the predominant strain in both study populations.

The authors of this study found no statistically significant difference in mean Ct values ​​between vaccinated and unvaccinated samples.They have Ct values ​​in both UeS and HYT samples<15から> Estimated to be 30. Similarly, the researchers also did not obtain a statistically significant difference in mean Ct values ​​between asymptomatic and symptomatic samples.

In this study, researchers also calculated Ct values ​​across different age groups, genders, and vaccine types. They reported that individuals with low Ct levels showed high viral load in all study groups, regardless of vaccine status, age, or gender. This result contradicts previous studies related to a large UK-based cohort that reported higher median Ct values ​​in vaccinated individuals than in unvaccinated individuals. .. Another study conducted in San Francisco found that fully vaccinated asymptomatic individuals showed significantly lower viral load than symptomatic and vaccinated individuals.

The results of the current study are with other recently published reports revealing similar viral load between vaccinated and unvaccinated individuals in scenarios related to delta variant infection. It matches. Similarly, the results of another study conducted in Wisconsin were similar to the reports of current studies that revealed similar Ct levels between vaccinated and unvaccinated cases. In Singapore and Massachusetts, individuals experiencing a vaccination breakthrough due to delta variant infection showed similar Ct levels to unvaccinated individuals.

The authors of this study strongly emphasized that the results obtained in this study are consistent throughout the study involving large cohorts using different assays and locations. The study found that asymptomatic, fully vaccinated individuals had low Ct levels and could be infected from a breakthrough infection before symptoms appeared. However, an early study conducted in Singapore showed that vaccinated individuals had a faster decrease in viral load than unvaccinated individuals.

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Over 20% of COVID-19-positive patients recovered, vaccinated individuals showed low Ct values ​​(<20), and one-third were asymptomatic at the time of testing. This highlights the need for additional research on the immunological status of such vaccine escapes and how infectious they are. More research is needed to determine the immunological status of a breakthrough case of vaccination or the reason for avoiding an immune response.

In addition, scientists have observed low Ct levels in some children (under 12 years of age) and children who are not yet eligible for vaccination. This indicates that children with high viral load are infectious and can spread the disease. Therefore, frequent COVID-19 testing in school children is essential for early detection to prevent further spread of the virus.

*Important Notices

medRxiv publishes unpeer-reviewed preliminary scientific reports and should not be considered definitive, guide clinical / health-related behaviors, or be treated as established information.