RR:C19 Evidence Scale rating by reviewer:
Reliable. The main study claims are generally justified by its methods and data. The results and conclusions are likely to be similar to the hypothetical ideal study. There are some minor caveats or limitations, but they would/do not change the major claims of the study. The study provides sufficient strength of evidence on its own that its main claims should be considered actionable, with some room for future revision.
I found this study a reliable one as it is statistically strong and the results are convincing. The results seem helpful in understanding the low seroprevalence worldwide despite a high rate of infection. Although, the finding of decline in seropositivity is a little contradictory from the findings of few studies in developing countries. However, the technique is different in other studies, so for a strong impact I would suggest a follow-up study of this research. It will be more conclusive and reflect the status quo as the whole world is affected by the second wave of SARS CoV2.
The limitations they mentioned are justified and, again, I would say a longitudinal study would be a better way to reach the conclusions, but cross-sectional surveys are acceptable in a pandemic as early results will help in prompt intervention and help in implementing public health measures.
Regarding presentation, I would suggest being more precise. At some points I lost the connection but, overall, it is acceptable. References are recent and grammar is also correct.
I would suggest accepting this paper for publishing in Rapid Reviews: COVID 19.