How does Vaccination Impact Viral Load and Duration of Illness in Those with Breakthrough SARS-CoV-2 Infection?
BACKGROUND AND PURPOSE:
Thompson et al. (NEJM, 2021) compared infection rates, mean viral RNA loads, and symptoms and the duration of illness among partially vaccinated, fully vaccinated, and non-vaccinated individuals
Prospective cohort study
Health care personnel, first responders, and other essential and frontline workers
mRNA-based COVID-19 vaccination status
Participants completed weekly SARS-CoV-2 testing (between December 14, 2020, to April 10, 2021)
The formula for calculating vaccine effectiveness was 100%×(1−hazard ratio for SARS-CoV-2 infection in vaccinated vs. unvaccinated participants)
Adjustments were made for the propensity to be vaccinated, study site, occupation, and local viral circulation
Time to RT-PCR–confirmed SARS-CoV-2 infection in vaccinated participants vs unvaccinated participants
Viral RNA load
Frequency of febrile symptoms and duration of illness among participants with SARS-CoV-2 infection
SARS-CoV-2 positive tests: 5% (204 participants)
Fully vaccinated (≥14 days after dose 2) participants: 5 cases
Partially vaccinated (≥14 days after dose 1 and <14 days after dose 2) participants: 11 cases
Unvaccinated participants: 156 cases
Adjusted vaccine effectiveness
Full vaccination: 91% (95% CI, 76 to 97)
Partial vaccination: and 81% (95% CI, 64 to 90)
Mean viral RNA load was significantly lower in partially or fully vaccinated participants with breakthrough infection vs unvaccinated
RNA Load: 40% lower (95% CI, 16 to 57)
The risk of febrile symptoms and duration of illness were also lower in the breakthrough vaccine group
Febrile illness: Relative risk 0.42 (95% CI, 0.18 to 0.98)
Duration of illness: 2.3 fewer days spent sick in bed (95% CI 0.8 to 3.7)
mRNA-based COVID-19 vaccines are highly effective at preventing infection in real-world conditions
91% with full vaccination
81% with partial vaccination
Among individuals who experienced breakthrough infection, vaccination also reduced the viral RNA load, risk of febrile symptoms, and duration of illness
The authors state
If further data confirm that the administration of mRNA vaccines reduces the number of viral RNA particles and the duration of viral RNA detection, thereby blunting the infectivity of SARS-CoV-2, then the overall results support that mRNA vaccines not only are highly effective in preventing SARS-CoV-2 infection but also may mitigate the effects of breakthrough infections — a finding that is especially important to essential and frontline workers, given their potential to transmit the virus through frequent close contact with patients, coworkers, and the public
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This educational activity may contain discussion of published and/or investigational uses of agents that are not indicated by the FDA. The planners of this activity do not recommend the use of any agent outside of the labeled indications.
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