Coronavirus Disease 2019 (COVID-19) has emerged at the end of 2019 from China and less than half a year was declared as a pandemic [1] . A rapid increase in the number of cases and deaths urged the scientific community to respond quickly and deal with the virus in a dual strategy: Treat the sick and find ways to halt the spread of the disease [2] . Vaccines got the spotlight and with an exceptional pace, different vaccine candidates were launched [3] . The incidence of COVID-19 related hospitalizations and deaths was reduced drastically upon the use of vaccines [4] .Vaccines were thought at first to prevent from Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection [5] . This seemed quite desirable and achievable at the start. But as more and more people got vaccinated, certain breaches occurred, though less common but significant importance was noted. Breakthrough infections were one such concern that shifted the focus much on symptomatology of the disease after many studies reported cases of infections within 1-7 d following vaccination [6,7] . It was established that "the vaccine provides protection Al-Raddadi et al.: Immunological Response to COVID-19 Vaccines in Pakistani Healthy Recipients Coronavirus disease 2019 mass vaccination has led to drastic reduction in hospitalizations and mortality. A number of case reports have emerged reporting coronavirus disease 2019 infection within days following vaccination. There is a need to understand development of immune antibodies in the early post-vaccination period. A prospective analysis of immunoglobulin M and immunoglobulin G kinetics was conducted during the first 28 d following vaccination with either CanSino or Sinovac vaccines in a cohort of 40 healthy volunteers. Serial blood samples were collected from the volunteers right before the first dose of vaccine (d 0) and then on d 4, d 7, d 14, d 21, d 24 and d 28 post-vaccination. Using enzyme-linked immunosorbent assay, circulating anti-severe acute respiratory syndrome coronavirus 2 receptor binding domain immunoglobulin M and immunoglobulin G antibodies were analyzed. Most vaccine recipients (31/40) did not develop any circulating immunoglobulin M. The remaining 9 recipients showed a typical immunoglobulin M curve with antibodies appearing on d 4, peaking on d 7 and declining on d 21 and beyond. Immunoglobulin G response was more typical within 38/40 recipients showing the appearance of immunoglobulin G on d 4, which continued till the end of the study period. This study demonstrates that vaccine-induced immunoglobulin M-based immunity cannot be relied during the first few days following vaccination and more time is needed to have a better picture of the real situation.