Effect of vaccination and of prior infection on infectiousness of vaccine breakthrough infections and reinfections

Abstract

SARS-CoV-2 breakthrough infections in vaccinated individuals and in those who had a prior infection have been observed globally, but the transmission potential of these infections is unknown. The RT-qPCR cycle threshold (Ct) value is inversely correlated with viral load and culturable virus. Here, we investigated differences in RT-qPCR Ct values across Qatar national cohorts of primary infections, reinfections, BNT162b2 (Pfizer-BioNTech) breakthrough infections, and mRNA-1273 (Moderna) breakthrough infections. Through matched-cohort analyses of the randomly diagnosed infections, the mean Ct value was higher in all cohorts of breakthrough infections compared to the cohort of primary infections in unvaccinated individuals. The Ct value was 1.3 (95% CI: 0.9-1.8) cycles higher for BNT162b2 breakthrough infections, 3.2 (95% CI: 1.8-4.5) cycles higher for mRNA-1273 breakthrough infections, and 4.0 (95% CI: 3.4-4.6) cycles higher for reinfections in unvaccinated individuals. Assuming a linear relationship between viral load and infectiousness, these differences imply that breakthrough infections are at least 50% less infectious than primary infections in unvaccinated individuals. Public health benefits of vaccination may have been underestimated, as COVID-19 vaccines not only protect against acquisition of infection, but also appear to protect against transmission of infection.

SARS-CoV-2 Reinfection Rate and Outcomes in Saudi Arabia: A National Retrospective Study

“…Therefore, to reduce the likelihood of future reinfections, the study suggests targeting this specific vulnerable group for COVID-19 vaccination, even if they have been previously infected with SARS-CoV-2. This is consistent with many studies, showing the additional protectivity of vaccines against infection among infected populations ( Abu-Raddad et al ., 2021a , 2021b ; Townsend et al ., 2021 ). Surprisingly, our study cohort consisted of young adults, with the majority of reinfected individuals under the age of 30.…”

“…Although our sequencing data are limited, we were still able to describe the association between the recrudescence of reinfected cases in Saudi Arabia and the reopening of the Kingdom, coinciding with the emergence of variants, supported by the high prevalence of delta variants in our cohort and the vaccination status among the sequenced subgroup of individuals, demonstrating a waning in vaccine protection against SARS-CoV-2 infection. However, we have shown here that severe illness resulting in intensive care hospitalizations and death in reinfected individuals is a rare phenomenon and mainly occurs among the unvaccinated group, suggesting acquired protection from multiple episodes of infection as shown by several studies ( Abu-Raddad et al ., 2021a , 2021c ). Multiple reinfections and vaccination, so-called hybrid immunity, should provide strong immune protection against severe and fatal diseases, which is reassuring given the frequent resurgence of cases worldwide ( Abu-Raddad et al ., 2021c ; Jeffery-Smith et al ., 2021 ).…”

Long-term adaptive response in COVID-19 vaccine recipients and the effect of a booster dose

“…These data provide a novel insight into long-term immunity to SARS-CoV-2 in previously infected subjects who exhibited marked immunological imprinting from previous infection, shaping the long-term breadth and maturation of neutralizing activity, even in the absence of a booster dose. These data indicate that pre-vaccination immunological memory plays a major role in dictating better vaccination outcomes and may explain why fewer breakthrough infections were reported in our cohort of previously infected subjects, in line with real-world data (52). After the booster dose, we did not find any changes in either the frequency of B cells specific for the spike protein of Wuhan Hu-1 (Figure 2B) or in the number of IgG + and IgA + CD27 + memory B cells (Figure 2C).…”

BNT162b2 and mRNA-1273 COVID-19 vaccine effectiveness against the SARS-CoV-2 Delta variant in Qatar

“…Higher effectiveness against infection with Delta after the second dose was estimated for mRNA-1273 compared to BNT162b2 (P = 0.009), in line with studies indicating a stronger induced immune response and protection for mRNA-1273 (refs. 5,[36][37][38] ).…”