Background
The Pfizer-BioNTech (BNT162b2) and Oxford-AstraZeneca (ChAdOx1 nCoV-19) COVID-19 vaccines have demonstrated excellent safety and efficacy in Phase 3 trials.
Our aim was to investigate the safety and efficacy of these vaccines in a UK community setting.
Methods
In this prospective observational study, we examined the proportion and probability of self-reported systemic and local side effects within 8 days of vaccination in people using the COVID Symptom Study app who received one or two doses of the BNT162b2 vaccine or one dose of the vaccine. Vaccine against ChAdOx1 nCoV-19.
We also compared infection rates in a subset of vaccinated people who were subsequently tested for SARS-CoV-2 with PCR or lateral flow testing with infection rates in unvaccinated controls.
All analyzes were adjusted for age (≤55 years vs. >55 years), sex, healthcare worker status (binary variable), obesity (BMI <30 kg/m2 vs. ≥30 kg/m2), and comorbidities (binary variable , with or without comorbidities).
Results
Between December 8 and March 10, 2021, 627,383 people reported being vaccinated with 655,590 doses: 282,103 received one dose of BNT162b2, of which 28,207 received a second dose, and 345,280 received one dose of ChAdOx1 nCoV-19.
Systemic side effects were reported in 13.5% (38,155 of 282,103) of individuals after the first dose of BNT162b2, 22 0% (6,216 of 28,207) after the second dose of BNT162b2, and 33 7% (116,473 of 345,280) after the first dose of ChAdOx1 nCoV-19. Local side effects were reported in 719% (150,023 of 208,767) of individuals after the first dose of BNT162b2, in 685% (9025 of 13,179) after the second dose of BNT162b2, and in 587% (104,282 of 177,655) of individuals. ) after the first. dose of ChAdOx1 nCoV-19. Systemic side effects were more common (16-fold after the first dose of ChAdOx1 nCoV-19 and 29-fold after the first dose of BNT162b2) among individuals with prior SARS-CoV-2 infection than among those without prior infection. known.
Local effects were equally greater in previously infected individuals than in those without known prior infection (14-fold after the first dose of ChAdOx1 nCoV-19 and 12-fold after the first dose of BNT162b2). 3,106 of 103,622 vaccinated individuals and 50,340 of 464,356 unvaccinated controls tested positive for SARS-CoV-2 infection.
Significant reductions in the risk of infection were observed starting 12 days after the first dose, reaching 60% (95% CI: 49-68) for ChAdOx1 nCoV-19 and 69% (66-72) for BNT162b2 at 21–44 days and 72% (63–79) for BNT162b2 after 45–59 days.
Discussion
In this large-scale community-based study in the UK, we have investigated adverse effects and infection rates following administration of the two COVID-19 vaccines being used in the UK.
The overall mean age of vaccinated app users was higher than that of the general population (40 3 years) however, it was lower than those of samples within other UK COVID-19 efficacy studies, in largely due to the presence of a small proportion of healthcare workers among the participants in this study. However, our study population was considerably larger than the study populations of the phase 3 trials.
We found that systemic adverse effects, including headache and fatigue, affected fewer than one in four people and were less common in the community than expected from clinical trials.
For example, in phase 3 clinical trials of the BNT162b2 vaccine, the most common events after the first dose were injection site pain (71–83%), fatigue (34–47%), and headache (25–42%). However, in our community analysis, less than 30% of users complained of injection site pain and less than 25% of fatigue and headache after the first dose.
Although side effects were significantly more prevalent in women than in men, in people 55 years of age or younger than in those over 55 years of age, and after the second dose than after the first dose, they occurred at much lower frequencies than expected. by the published study. literature.
For example, while 51-59% of participants reported fatigue after the second dose of BNT162b2 in the phase 3 trial of that vaccine, less than 15% of participants reported fatigue after the second dose in our study. Furthermore, our data provide community evidence to support early reports of a higher frequency of side effects in younger people than in older people.
Similarly, rates of side effects after the ChAdOx1 nCoV-19 vaccine were lower than expected. The Phase 2-3 trial of the ChAdOx1 nCoV-197 vaccine reported systemic adverse effects in 88% of participants aged 18 to 55 years who received the first injection, while we found a lower rate of 33% after the first dose in the general sample and 46% in people aged 18 to 55 years (data not shown).
People vaccinated with the ChAdOx1 nCoV-19 vaccine were more likely to experience systemic side effects than those who had received the BNT162b2 vaccine, but in our study 89% of respondents who recorded at least one systemic side effect after the ChAdOx1 nCoV vaccine -19 reported no systemic effects after 3 days, and 98 3% reported no effects after 1 week.
In conclusion , the short-term adverse effects of both vaccines are moderate in frequency, mild in severity, and short in duration. Adverse effects are reported more frequently in younger people, women, and among those who previously had COVID-19.
Post-vaccine symptoms (both systemic and local) usually last 1 to 2 days from the injection.
Our data could be used to inform people about the likelihood of side effects based on their age and sex and the type of vaccine being given. Furthermore, our data support the results of randomized controlled trials in a large community setting showing evidence of reduced infection after 12 days and substantial protection after 3 weeks.
Interpretation
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