Adverse effect profile of COVID-19 vaccine in Northern Nigeria: a prospective observational study

In March 2021, the Nigerian Government approved Coronavirus 2019 (COVID-19) vaccines, including CHAd0x1 nCov-19, Ad26.Cov2.S, mRNA-1273 and BNT162b2. Many, including healthcare workers, expressed hesitancy due to potential adverse effects. We conducted an observational study to assess the adverse effects of post-vaccination. We followed vaccinated and unvaccinated cohorts daily for 7 days and then weekly for 3 weeks. We compared adverse effects between groups. Vaccinated participants were 21 times more likely to experience an adverse effect (Relative Risk, RR=21.30; 95% Confidence Interval, 95%CI=8.107-56.012) and 4 times more likely to experience systemic adverse effects (RR=3.97; 95%CI=1.70-9.27) when compared to unvaccinated participants. Female participants were significantly associated with the development of both local and systemic adverse effects, X2=77.9% (p≤0.001) and X2=47.1% (p=0.0037), respectively. Up to 81.6% of second-dose vaccine recipients compared to 68.4% of first-dose vaccine recipients developed at least one adverse effect, X2=5.25 (p=0.071). None of the vaccinated participants developed severe adverse effects during the study period. Adverse effects from COVID-19 vaccination are common, but generally safe and tolerable. Females play a significant role in reporting adverse effects. Both systemic and local adverse effects are expected to resolve within a few days post-vaccination.