ABSTRACT
Background: The ability of SARS-CoV-2 vaccines to protect against infection and onward transmission determines whether immunisation can control global circulation. We estimated effectiveness of BNT162b2 and ChAdOx1 vaccines against acquisition and transmission of the Alpha and Delta variants in a prospective household study in England. Methods: Adult index cases in the community and their household contacts took oral-nasal swabs on days 1, 3 and 7 after enrolment. Swabs were tested by RT-qPCR with genomic sequencing conducted on a subset. We used Bayesian logistic regression to infer vaccine effectiveness against acquisition and transmission, adjusted for age, vaccination history and variant. Findings: Between 2 February 2021 and 10 September 2021 213 index cases and 312 contacts were followed up. After excluding households lacking genomic proximity (N=2) or with unlikely serial intervals (N=16), 195 households with 278 contacts remained of whom 113 (41%) became PCR positive. Delta lineages were 4.6 times (95% Credible Interval: 1.5 - 20.1) more transmissible than Alpha; contacts older than 18 years were 2.0 times (1.4 - 3.3) more likely to acquire infection than children. Effectiveness of two doses of BNT162b2 against transmission of Delta was 31% (-3%, 61%) and 42% (14%, 69%) for ChAdOx1, similar to their effectiveness for Alpha. Protection against infection with Alpha was higher than for Delta, 71% (12%,95%) vs 24% (-2%, 64%) respectively for BNT162b2 and 26% (-39%, 73%) vs 14% (-5%, 46%) respectively for ChAdOx1. Interpretation: BNT162b2 and ChAdOx1 reduce transmission of the Delta variant from breakthrough infections in the household setting though their protection against infection is low. Funding: This study was funded by the UK Health Security Agency (formerly Public Health England) as part of the COVID-19 response.
Subject(s)
COVID-19ABSTRACT
In January 2020, the United Kingdom (UK) removed one of the two infant doses of the 13-valent pneumococcal conjugate vaccine (PCV13), leaving a single priming dose at 3 months and a 12 month booster. We modelled the potential impact on invasive pneumococcal disease (IPD) of a drop in PCV13 coverage associated with the restrictions on non-essential health care visits introduced to combat COVID-19 in the UK on 23 March 2020. Using a previously published model of pneumococcal transmission in England and Wales we simulated the impact of reducing PCV13 coverage by 50% for 3 months from 23 March without subsequent catch-up vaccination. To implement social distancing, we reduced mixing between and within age-groups by either 10% or 50%. In a sensitivity analysis we explored the effect of complete cessation of PCV13 vaccination during the lockdown and of extending its duration to 6 months. Annual numbers of IPD cases predicted by the model under different vaccination and lockdown scenarios with uncertainty intervals (UI) generated from the minimum and maximum values of the model predictions using 500 parameter sets with values within a pre-specified range of the maximum likelihood set. The model predicted that any increase in IPD cases from a reduction in PCV13 coverage would be more than offset by a reduction in pneumococcal transmission due to social distancing, with a net reduction in cumulative IPD cases (UI -1,479, -1,061, all ages) over the next five years. Similar results were obtained in the sensitivity analysis, though with a greater reduction with a 6 month lockdown. COVID-19 social distancing measures are predicted to have had a profound effect on pneumococcal transmission resulting in a reduction in pneumococcal carriage prevalence and IPD incidence over the first two years after the lockdown. Carriage studies will be informative in confirming the predicted impact of the social distancing measures after they have been lifted.