Impact of Delta on viral burden and vaccine effectiveness against new SARS-CoV-2 infections in the UK

Abstract

The effectiveness of BNT162b2, ChAdOx1, and mRNA-1273 vaccines against new SARS-CoV-2 infections requires continuous re-evaluation, given the increasingly dominant Delta variant. We investigated the effectiveness of the vaccines in a large community-based survey of randomly selected households across the UK. We found that the effectiveness of BNT162b2 and ChAd0x1 against any infections (new PCR positives) and infections with symptoms or high viral burden is reduced with the Delta variant. A single dose of the mRNA-1273 vaccine had similar or greater effectiveness compared to a single dose of BNT162b2 or ChAdOx1. Effectiveness of two doses remains at least as great as protection afforded by prior natural infection. The dynamics of immunity following second doses differed significantly between BNT162b2 and ChAdOx1, with greater initial effectiveness against new PCR-positives but faster declines in protection against high viral burden and symptomatic infection with BNT162b2. There was no evidence that effectiveness varied by dosing interval, but protection was higher among those vaccinated following a prior infection and younger adults. With Delta, infections occurring following two vaccinations had similar peak viral burden to those in unvaccinated individuals. SARS-CoV-2 vaccination still reduces new infections, but effectiveness and attenuation of peak viral burden are reduced with Delta.

Mathematical Modeling of Vaccines That Prevent SARS-CoV-2 Transmission

“…Serial assessment for infection in British households suggests high vaccine induced protection against SARS-CoV-2, including the dominant variant of concern B.1.1.7 or alpha during the fourth wave of infection in spring 2021. More, recently there has been some erosion in VE SUSC associated with the predominance of B.1.167.2 or delta [6]. While not providing a precise estimate of VE SUSC , these data suggest that at least some observed efficacy against disease in clinical trials is mediated by complete protection against infection.…”

“…Five VE SUSC and VE SYMP combinations (5 × 3 or 15 scenarios when considering the 3 values of VE INF ): VE SUSC = 90%/VE SYMP = 10%; VE SUSC = 10%/VE SYMP = 90%; VE SUSC = 90%/VE SYMP = 50%; VE SUSC = 50%/VE SYMP = 90%; VE SUSC = 90%/VE SYMP = 90%) would be compatible with current projections for the Moderna and Pfizer mRNA vaccines against B.1.1.7 which had estimated VE DIS = 95% and 90%, respectively [4,5]. Three combinations or nine scenarios (VE SUSC = 50%/VE SYMP = 50%; VE SUSC = 50%/VE SYMP = 10%; VE SUSC = 10%/VE SYMP = 50%) would be realistic if there is a relative decrease in VE DIS due to new viral variants as appears to be occurring with the now predominant B.1.617.2 variant of concern [6]. These lower vaccine estimates may also be relevant for other vaccines in development, or after a single dose of the Moderna or Pfizer product.…”

“…The FDA benchmark for licensure is a point estimate of VE DIS > 50% with a lower alpha-adjusted 95% confidence limit exceeding 30% [3]. The two mRNA vaccines which have been widely used across the United States showed high levels of protection (>90%) in trials and upon follow up [4][5][6].…”

Design of T cell epitope-based vaccine candidate for SARS-CoV-2 targeting nucleocapsid and spike protein escape variants

“…Of particular concern currently is the Delta variant that is spreading globally, as recent data suggests that both the AstraZeneca and Pfizer vaccines are slightly less effective against this variant in preventing COVID-19 related symptoms compared to the Alpha variant [75]. A recent large-scale study of Delta infections in the UK found that the protection offered against the variant by the AstraZeneca and Pfizer vaccines wanes with time, further supporting the need for variant-specific vaccines to boost immunity against variants of concern [76]. Despite global vaccination efforts, the rise in COVID-19 cases around the world as the Delta variant of SARS-CoV-2 spreads implies that variant-specific booster shots may be needed to combat emerging variants.…”

Viral loads of Delta-variant SARS-CoV2 breakthrough infections following vaccination and booster with the BNT162b2 vaccine

“…Nevertheless, only a slight decline was observed in preventing severe disease and its consequences 20,21 . Considering differential effectiveness against the Delta variant, reports vary substantially as to whether, and to what extent, the vaccine is effective in reducing viral loads of BTI with the Delta variant 8,[22][23][24][25][26][27][28][29][30][31][32] .…”