In a recent study published within the Journal of the American Medical Association, researchers investigated the association between two or three doses of the messenger ribonucleic acid (mRNA) coronavirus disease 2019 (COVID-19) vaccine and viral loads and symptoms during infections with different severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants.

Study: Association of mRNA Vaccination with Clinical and Virologic Features of COVID-19 Amongst US Essential and Frontline Employees. Image Credit: Studio Romantic/Shutterstock

Background

Community cohort studies reported a big decrease within the severity of COVID-19 symptoms, viral shedding, and duration of infection after widespread COVID-9 vaccination efforts. Nonetheless, the emergence of immune-evading SARS-CoV-2 variants of concern and the waning of vaccine-induced immunity is increasing breakthrough infections, albeit with mild symptoms.

Mild or moderate COVID-19 severity is observed in most SARS-CoV-2 infections, and such cases are thought to contribute significantly to the spread of COVID-19. Nonetheless, the information on such cases, in addition to information on routine community testing and the presence of multiple SARS-CoV-2 variants in a population, is proscribed. Such data are essential to know the efficacy of vaccinations against the severity of infections from SARS-CoV-2 variants.

Concerning the study

In the current study, the researchers used a prospective cohort of frontline and essential staff in six states in the US (U.S.) to review the virological and clinical characteristics of SARS-CoV-2 infections from the unique strain and Delta and Omicron lineages and compare clinical outcomes and viral loads. The study also investigated the association between two and three mRNA vaccine doses and COVID-19 symptoms, severity, and viral load.

Frontline or essential staff as individuals whose occupation requires 20 hours or more of standard contact with others, resembling those working within the education, medical, waste management, and transportation sectors. The info comprised sociodemographic characteristics, SARS-CoV-2 infection history, and chronic medical conditions. Vaccination cards and online surveys were used to assemble details about COVID-19 vaccination status.

Nasal swabs were collected from the participants every week and tested using reverse transcriptase–polymerase chain response (RT-PCR). Whole genome sequencing was used to discover the viral lineage, and quantitative RT-PCR was performed to evaluate viral loads. For samples with a cycle threshold value greater than 30 with identified viral lineages, plaque-forming units (PFU) on Vero cells were used to find out the viability of the virus.

The clinical outcomes measured within the study were the presence and variety of COVID-19 symptoms, duration of the infection, days spent in bed for a minimum of half a day, variety of days away from work, and the medical care requirements. The virological outcomes measured were PFU counts and viral loads.

Results

The outcomes reported that of the 1199 COVID-19 infections within the cohort, the chances of infections from the unique strain, Delta variant, and Omicron variant were 14%, 24%, and 62%, respectively. The severity of symptoms was correlated to the vaccination doses.

Individuals with two doses of the vaccine were less symptomatic during Delta infections than unvaccinated individuals. A 3rd vaccine dose one to 21 weeks before infection significantly reduced the incidence of fever and chills and the duration of the symptoms.

The severity of symptoms during infections with the Omicron variant didn’t vary much between individuals with two vaccine doses and no vaccination. Still, individuals with three vaccine doses were significantly less prone to experience fever and chills or require medical attention than unvaccinated individuals.

The virological outcomes indicated that individuals who contracted the Delta or Omicron infection two to 21 weeks after the second vaccination dose had significantly lower viral loads than unvaccinated individuals. The viral loads during Omicron BA.1 infections were higher than during infections with the unique strain and just like the Delta infection viral loads. The durations of Omicron infections were shorter, and the symptoms were milder.

The authors imagine that the upper viral load combined with the high frequency of mild or asymptomatic cases could explain the increased transmissibility observed through the Omicron prevalence period.

Conclusions

Overall, the study indicated that two or three doses of mRNA vaccines lower than 150 days before contracting a SARS-CoV-2 infection significantly reduced the severity, duration, and viral load of Delta or Omicron infections in frontline staff. The vaccine doses also reduced the necessity to seek medical care.

In line with the authors, the high transmissibility of Omicron variants could possibly be related to the upper viral loads and milder symptoms during Omicron infections as in comparison with infections with the unique strain.

Journal reference:

• Joseph, G., Barnes, J., Azziz-Baumgartner, E., Arvay, M., Fry, A., Hall, A., Kutty, P., MacNeil, A., Donald, L. C., Reynolds, S., Schrag, S., Shang, N., Slaughter, R., Thornburg, N., Verani, J., Wang, R., Hunt, D. R., Sokol, B., Bloodworth, R., & Douglas, C. (2022). Association of mRNA Vaccination with Clinical and Virologic Features of COVID-19 Amongst US Essential and Frontline Employees. JAMA. doi: https://doi.org/10.1001/jama.2022.18550 https://jamanetwork.com/journals/jama/fullarticle/2797418