Study Title:

Vaccine after Effects and Post-Vaccine Infection in a Real World Setting: Results from the COVID Symptom Study

Study Abstract

Background: The Pfizer-BioNTech (BNT162b2) and the Oxford/AstraZeneca (ChAdOx1 nCoV-19) COVID-19 vaccines have shown excellent safety and efficacy in Phase III trials. Here we report results from a real world setting on the two most administered vaccines in the UK.

Methods: We investigated self-reported systemic and local effects within eight days of vaccination in 387,471 individuals from the COVID Symptom Study app who received one (n=209,251) or two (n=13,478) doses of the BNT162b2 vaccine, or one dose of ChAdOx1 nCoV-19 vaccine (n=178,220) between December 8 and February 15 2021. A subset of individuals subsequently tested for SARS-CoV-2 were studied for infection rates from PCR or lateral flow test results post-vaccination (59,639 vaccinated vs 277,599 controls).

Findings: Systemic side effects were reported in 11.8% of participants after the first BNT162b2 dose, 20.3% after the second BNT162b2 dose, and 29.4% after the first ChAdOx1 nCoV-19 dose. Systemic effects were more prevalent among individuals with pre-existing COVID-19 infection (BNT162b2:34.1%; ChAdOx1 nCoV-19:51.6%) than among individuals without known prior infection (BNT162b2:10.6%; ChAdOx1 nCoV-19:28.6%) and among those aged <55 years (BNT162b2:19.9%; ChAdOx1 nCoV-19:45.3%) compared to those aged >55 years (BNT162b2:9.2%, ChAdOx1 nCoV-19: 26.9%). We observed significant reduction in infection risk 12-21 days after the first dose (BNT162b2:-57% [-71%, -38%], ChAdOx1 nCoV-19:-42% [-71%, -17%]).

Interpretation: This phase IV-type study assessing both BNT162b2 and ChAdOx1 nCoV-19 vaccines identifies mild systemic side effects affecting 11-30% of individuals post-vaccination, lower than in published Phase III trials. Our data on infection post-vaccine were also reassuring.

Study Information

App. Available at SSRN:

Full Study