Coronavirus disease 2019 (COVID-19) is an infectious disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which first appeared in China, in December 2019 and is now spreading worldwide and poses a great threat to public health. In 12th July 2020, the total number of cases worldwide was about 13 million cases with case fatality rate of 4.4% and in Egypt the total cases was 81158 and case fatality rate was 4.6%. (1,2).

In recent years, novel coronaviruses emerge periodically in different areas around the world. Severe acute respiratory syndrome coronavirus (SARS-CoV) occurred in 2002, which reportedly infected 8422 people with about 10% case fatality rate (3). Middle East respiratory syndrome coronavirus (MERS-CoV) was first identified in 2012 in Saudi Arabia, bringing a total of 1401 MERS-CoV infections, and about 35% case fatality rate (1). All the infection cases and recent epidemics show that coronaviruses impose a continuous threat to human beings and the economy as they emerge unexpectedly, spread easily, and lead to catastrophic consequences.

As the number of recovered patients with COVID-19 continues to be increasing, the strength and duration of immunity after infection is an important point to be studied. Moreover, understanding this issue is a critical point for controlling this epidemic as they are the key for herd immunity and for informing decisions on how and when to ease physical distancing restrictions and to be ready for other waves of the infection. There is currently no evidence if the people who have recovered from COVID-19 have antibodies and protected from a second attack of infection or future wave of this pandemic or not. Therefore, we will carry out a longitudinal study of immunity in recovered patients to assess SARS-Cov2 patients' risk for future reinfection.

Inclusion Criteria:

• Adults aged ≥ 20 years.
• Prior COVID-19 infection confirmed by PCR detection of SARS-CoV-2 RNA or antigen in nasopharyngeal swab.
• Recovery from infection either confirmed by two consecutive negative PCR (collected ≥24 hours apart) or passing of 14 days since onset of COVID-19 symptoms and at least 3 days since resolution of fever without the use of antipyretics and improvement of respiratory symptoms

Exclusion Criteria:

• Presence of any chronic illness interfere with immunity (autoimmune diseases).
• Pregnancy.
• Recovery from three months or more.

Patients recovered from COVID-19 infection within three months before the start of the study.