Impact of vaccination on new infections
Impact of vaccination on new SARS-CoV-2 infections in the United Kingdom
Using 1,945,071 real-time PCR results from nose and throat swabs taken from 383,812 participants between 1 December 2020 and 8 May 2021, we found that vaccination with the ChAdOx1 or BNT162b2 vaccines already reduced SARS-CoV-2 infections ≥21 d after the first dose (61% (95% confidence interval (CI) = 54–68%) versus 66% (95% CI = 60–71%), respectively), with greater reductions observed after a second dose (79% (95% CI = 65–88%) versus 80% (95% CI = 73–85%), respectively). The largest reductions were observed for symptomatic infections and/or infections with a higher viral burden. Overall, COVID-19 vaccination reduced the number of new SARS-CoV-2 infections, with the largest benefit received after two vaccinations and against symptomatic and high viral burden infections, and with no evidence of a difference between the BNT162b2 and ChAdOx1 vaccines.
Community-level evidence for SARS-CoV-2 vaccine protection of unvaccinated individuals
Here, by analyzing vaccination records and test results collected during the rapid vaccine rollout in a large population from 177 geographically defined communities, we find that the rates of vaccination in each community are associated with a substantial later decline in infections among a cohort of individuals aged under 16 years, who are unvaccinated. On average, for each 20 percentage points of individuals who are vaccinated in a given population, the positive test fraction for the unvaccinated population decreased approximately twofold. These results provide observational evidence that vaccination not only protects individuals who have been vaccinated but also provides cross-protection to unvaccinated individuals in the community.
The specter of Manaus: the risks of a rapid return to pre-pandemic conditions after COVID-19 vaccine rollout
[Preprint.] In this work we model the situation in the United States at present, to demonstrate how the P.1 variant of SARS-CoV-2 can cause a rebound wave of COVID-19 in a matter of months, similar to what happened in Manaus at the beginning of this year. A high burden of morbidity (and likely mortality) remains possible, even if the vaccine is partially effective against new variants and widely accepted. Our modeling suggests that variants that are already present within the population may be capable of quickly defeating the vaccines as a public health intervention, a fatal flaw in strategies that emphasize rapid reopening before achieving control of SARS-CoV-2.
Neutralising antibody activity against SARS-CoV-2 VOCs B.1.617.2 and B.1.351 by BNT162b2 vaccination
Two doses of BNT162b2 elicited ELISA-detected anti-Wild-type spike antibodies in all participants, and NAb activity against all strains, including the three VOCs tested, in all except six (3%) and nine (5%) of 159 participants who lacked NAb activity against B.1.617.2 and B.1.351, respectively (appendix p 2). NAbTs of sera correlated well between Wild-type and variants (appendix p 2; RS>0·82, p<2 × 10−16), as well as between VOCs (B.1.617.2 vs B.1.351: RS=0·85, p<2 × 10−16). However, NAbTs were 5·8-fold reduced against B.1.617.2 relative to Wild-type (95% CI 5·0–6·9), significantly more reduced than against B.1.1.7 (2·6-fold vs Wild-type, 95% CI 2·2–3·1), and on a similar order to the reduction observed against B.1.351 (4·9-fold vs Wild-type, 95% CI 4·2–5·7). These data, together with epidemiological data of B.1.617.2 growth, raise the possibility that this VOC presents a dual challenge of reduced vaccine efficacy akin to the B.1.351 VOC, and increased transmissibility beyond the B.1.1.7 VOC.
Previous COVID-19 infection, but not Long-COVID, is associated with increased adverse events following BNT162b2/Pfizer vaccination
Of 974 healthcare workers (aged 19-72-years) responding to the survey and providing complete data for analysis, 265 (27%) participants (84% female, mean-age 48.9) reported a prior positive PCR and/or antibody result, and 709 (80% female, mean-age 47.0) had no COVID-19 history. Figure 1 A shows frequencies of each symptom by COVID-19 status. The proportion of participants reporting at least one moderate-to-severe symptom was higher in the previous COVID-19 group (56% v 47%, OR=1.5 [95%CI, 1.1–2.0], p=.009).