Fully vaccinated US frontline workers may experience reduced severity, duration, and viral shedding during SARS-CoV-2

In a recently published study in the Journal of the American Medical AssociationThe researchers examined the association between two or three doses of messenger ribonucleic acid (mRNA) Coronavirus Disease 2019 (COVID-19) vaccine and viral loads and symptoms during infections with different severe acute respiratory variant coronavirus 2 (SARS-CoV-2). syndrome .

background

Community cohort studies reported significant decreases in COVID-19 symptom severity, virus shedding, and duration of infection following widespread COVID-9 immunization efforts. However, the emergence of worryingly immune-avoidant SARS-CoV-2 variants and the waning of vaccine-induced immunity are leading to an increase in breakthrough infections, albeit with mild symptoms.

Mild or moderate COVID-19 severity is observed in most SARS-CoV-2 infections, and such cases are believed to contribute significantly to the spread of COVID-19. However, data on such cases, as well as information on routine community testing and the presence of multiple SARS-CoV-2 variants in a population, is limited. Such data are essential to understand the effectiveness of vaccinations against the severity of infections caused by SARS-CoV-2 variants.

About the study

In the present study, researchers examined the virological and clinical characteristics of SARS-CoV-2 infections of the original strain and the Delta and Omicron lines and a prospective cohort of frontline workers and key workers in six states of the United States ( UNITED STATES). Compare clinical outcomes and viral loads. The study also examined the association between two and three mRNA vaccine doses and COVID-19 symptoms, severity and viral load.

Frontline workers or essential workers are individuals whose job requires at least 20 hours of regular contact with others, such as: B. Employees in education, medicine, waste management and transportation. The data included sociodemographic characteristics, SARS-CoV-2 infection history and chronic diseases. Vaccination cards and online surveys were used to gather information on COVID-19 vaccination status.

Nasal swabs were taken from participants every week and tested using reverse transcriptase polymerase chain reaction (RT-PCR). Whole genome sequencing was used to identify the viral lineage and quantitative RT-PCR was performed to determine viral load. For samples with a cycle threshold greater than 30 with identified virus lines, plaque forming units (PFU) on Vero cells were used to determine virus viability.

The clinical outcomes measured in the study were the presence and number of COVID-19 symptoms, duration of infection, days spent in bed at least half a day, number of days off work, and medical care needs. The virological outcomes measured were PFU counts and viral loads.

Results

The results showed that of the 1199 COVID-19 infections in the cohort, the percentages of infections by the original strain, delta variant and omicron variant were 14%, 24% and 62%, respectively. Symptom severity was correlated with vaccine doses.

Individuals who received two doses of the vaccine had fewer symptoms during Delta infections than non-vaccinated individuals. A third dose of vaccine 1 to 21 weeks before infection significantly reduced the incidence of fever and chills and the duration of symptoms.

The severity of symptoms for infections with the Omicron variant did not differ much between people with two doses of vaccine and those without vaccination. However, people who received three doses of the vaccine were significantly less likely to develop fever and chills or require medical attention than unvaccinated people.

Virological results showed that subjects infected with either Delta or Omicron infection two to 21 weeks after the second dose of vaccine had significantly lower viral loads than unvaccinated subjects. Viral loads during Omicron BA.1 infection were higher than during infections with the original strain and similar to the viral load of Delta infection. The duration of the Omicron infections was shorter and the symptoms were milder.

The authors believe that the higher viral load combined with the high frequency of mild or asymptomatic cases could explain the increased transmissibility observed during the omicron prevalence period.

Conclusions

Overall, the study showed that two or three doses of mRNA vaccines less than 150 days before contracting SARS-CoV-2 infection significantly reduced the severity, duration and viral load of Delta or Omicron infections in frontline workers . The vaccine doses also reduced the need to seek medical help.

According to the authors, the high transmissibility of the Omicron variants could be related to the higher viral load and the milder symptoms in Omicron infections compared to infections with the original strain.