Effectiveness of BNT162b2 and ChAdOx1 against SARS-CoV-2 household transmission: a prospective cohort study in England

Abstract

SummaryBackgroundThe 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.MethodsAdult 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.FindingsBetween 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 had 1.64 times the risk (95% Credible Interval: 1.15 – 2.44) of transmission than Alpha; contacts older than 18 years were 1.19 times (1.04 - 1.52) 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.InterpretationBNT162b2 and ChAdOx1 reduce transmission of the Delta variant from breakthrough infections in the household setting though their protection against infection is low.FundingThis study was funded by the UK Health Security Agency (formerly Public Health England) as part of the COVID-19 response.

Household Secondary Attack Rates of SARS-CoV-2 by Variant and Vaccination Status

“…We identified 2097 records (1791 from PubMed, 306 from medRxiv, and 2 from reference lists of eligible articles) published between June 18, 2021, and March 8, 2022 (eFigure 1 in the Supplement ). Fifty-eight new studies 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 (eTable 2 in the Supplement ) were combined with 77 studies from ou...…”

SARS-CoV-2: from herd immunity to hybrid immunity

“…With the exception of the Alpha variant, these VOC were not neutralized as effectively by antibodies derived from previous SARS-CoV-2 infections or primary vaccination regimens. For example, the effectiveness of two doses of either BNT162b2 or ChAdOx1 against transmission of Delta and Alpha was modest (in the range of 31–42%) 2 . Subsequent reports on the reduction of vaccine efficacy against Omicron infection, most notably for primary vaccine-induced protection 3 , emphasized the increasing complexity of trying to control SARS-CoV-2.…”

Epidemiological impact and cost-effectiveness analysis of COVID-19 vaccination in Kenya

“…[14] We assumed an effectiveness of 0% to 35% and 0% to 69% against onward transmission, per infection (delta variant), after either the first or second dose. [15] We assume that immunity due to either past infection of vaccination eventually wanes to 70% protection against disease and 0% protection against infection, with a mean time to complete waning of 460 days after the second dose of vaccine and 5 years following natural infection. [16] Furthermore, we assume that protection due to prior infection combined constructively with vaccination; that is that people who had previously had a natural infection episode of SARS-CoV-2 were further protected from reinfection by vaccination (see supporting information ).…”

“…[31–34] Therefore, to determine the robustness of the epidemiological model predictions to the vaccine effectiveness parameter values, we performed a sensitivity analysis across a range of values using a vaccine waning effectiveness model fitted to the UK Health Security Agency (UKHSA) COVID-19 data. [14,15]…”

“…[31][32][33][34] Therefore, to determine the robustness of the epidemiological model predictions to the vaccine effectiveness parameter values, we performed a sensitivity analysis across a range of values using a vaccine waning effectiveness model fitted to the UK Health Security Agency (UKHSA) COVID-19 data. [14,15] A univariate sensitivity analysis was done on the economic model to determine the robustness of the unit cost estimates with variations in vaccine procurement costs (base cost of $3 and $10 used) and discounting rates of DALYs (rate of 0% used). Further, given the current evidence gap to confidently determine the magnitude of underreporting of COVID-19 deaths, [35] the baseline cost-effectiveness analysis assumed an under-reporting of hospitalization and deaths by a factor of 5 and a one-way sensitivity analysis was done by varying the under-reporting factor (1)(2)(3)(4).…”