Local and systemic adverse effects were found to be less common among individuals in the United Kingdom who received the COVID-19 vaccine compared with those reported during phase 3 trials, according to results of a prospective observational study published in Lancet Infectious Diseases. The study also found that both the Pfizer-BioNTech and Oxford-AstraZeneca vaccines significantly decreased the risk for SARS-CoV-2 infection 12 days after administration of the first dose.

Between December and March 2021, investigators analyzed data from the UK’s COVID Symptom Study app that captured individuals’ self-reported systemic and local adverse effects within 8 days of receiving the first or second dose of either the Pfizer-BioNTech or Oxford-AstraZeneca COVID-19 vaccines. The investigators adjusted the data to account for differences in the population, such as vaccine type, age, sex, healthcare worker status, and comorbidities. They also compared COVID-19 infection rates of individuals who received the first dose of either vaccine vs unvaccinated controls.

The mean age of individuals who used the app during the study period was 50.6 years (SD, 19.2), and 4.8% were healthcare workers. The proportion of individuals reporting at least 1 systemic adverse effect after receiving the first vaccine dose was significantly increased among those aged 55 years and younger for both the Pfizer-BioNTech (odds ratio [OR], 2.19; 95% CI, 2.14-2.24; P <.0001) and Oxford-AstraZeneca vaccines (OR, 1.99; 95% CI, 1.96-2.03; P <.0001). Compared with men, women were more likely to report local and systemic adverse effects after receiving the first dose of either the Pfizer-BioNTech (OR, 1.89; 95% CI, 1.85-1.94; P <.0001) or Oxford-AstraZeneca vaccines (OR, 1.82; 95% CI, 1.79-1.85; P <.0001). The most common systemic adverse effects were headache and fatigue, and the most common local adverse effects were pain and tenderness at the injection site.


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Of 282,103 individuals who received the first dose of the Pfizer-BioNTech vaccine, 13.5% reported systemic adverse effects, which was significantly less than the 33.7% of 345,280 individuals who received the first dose of the Oxford-AstraZeneca vaccine (P <.0001). Of 28,207 individuals who subsequently received a second dose of the Pfizer-BioNTech vaccine, 22% reported systemic adverse effects. In addition, systemic adverse effects occurred more frequently after the first dose of the Oxford-AstraZeneca vaccine than after the second dose of the Pfizer-BioNTech vaccine (P <.0001).

In regard to the Pfizer-BioNTech vaccine, local adverse effects were reported by 71.9% (N=208,767) of individuals following the first dose and 38.5% (N=13,179) following the second dose (P <.0001). Of the individuals who received the Oxford-AstraZeneca vaccine, 58.7% (N=104,282) reported local adverse events following the first dose (P <.0001).

Individuals previously infected with SARS-CoV-2 were significantly more likely than those without a known history of infection to develop local and systemic adverse effects after receiving the first dose of either the Oxford-AstraZeneca (OR, 2.31; 95% CI, 2.23-2.38; P <.0001) or Pfizer-BioNTech vaccines (OR, 3.97; 95% CI, 3.83-4.12; P <.0001), and the second dose of the Pfizer-BioNTech vaccine (OR, 2.37; 95% CI, 2.17-2.60; P <.0001).

Of 103,622 vaccinated individuals and 464,356 unvaccinated controls, results of polymerase chain reaction testing and lateral flow assay showed that 3% and 11% were positive for SARS-CoV-2 infection, respectively.

Beginning 12 days after administration of the first dose of either vaccine, the risk for infection significantly decreased. At 21 to 44 days, the risk for infection decreased by 60% (95% CI, 49-68)  and 69% (95% CI, 66-72) among individuals who received the AstraZeneca and Pfizer-BioNTech vaccines, respectively. At 45 to 59 days, the risk for infection decreased by 72% (95% CI, 63-79) among those who received the Pfizer-BioNTech vaccine. Vaccinated individuals aged 55 years and younger also had a significantly decreased risk for infection compared with those older than 55 years, with similar findings noted among vaccinated individuals without comorbidities compared with those who had at least 1 comorbidity.

The study was limited by the self-reported nature of the data and potential selection bias for healthcare workers in regard to those tested for SARS-CoV-2 infection after vaccination. In addition, none of the individuals who used the COVID Symptom Study app had received a second dose of the AstraZeneca vaccine during the study period.

“Our data could be used to inform people on the likelihood of [adverse] effects on the basis of their age and sex and the type of vaccine being administered,” the investigators noted. They also noted that compared with existing phase 3 trial data, both vaccines were associated with a significantly decreased rate of severe and mild adverse effects.

Disclosure: Some study author(s) declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of disclosures. 

Reference

Menni C, Klaser K, May A, et al. Vaccine side-effects and SARS-CoV-2 infection after vaccination in users of the COVID Symptom Study app in the UK: a prospective observational study. Lancet Infect Dis. Published online April 27, 2021. doi:10.1016/S1473-3099(21)00224-3