Evaluation of the Immune Response in Symptomatic and Asymptomatic Patients' Diagnosed Witih COVID-19

The 2019-20 coronavirus disease, caused by COVID-19, is an ongoing pandemic. The outbreak started in Wuhan, Hubei province, China, in December 2019 and the World Health Organization (WHO) recognized it as a pandemic on 11 March 2020. Up to Apr 9. 2020 there are more than 1.4 million confirmed cases, and over 82,000 deaths 1. In Israel, COVID-19 was confirmed in more 9,000 cases and took the life of 70 victims (09.04.2020) .

With the extensive outbreak of COVID-19, a mass of studies with a large population have been reported. Wu et al. found that the mean R0 of COVID-19 was approximately 2.68(95% CI: 2.47-2.86) . The measures in which public health officials quarantine confirmed and isolate symptomatic cases in order to reduce the spread COVID-19 is the common practice used in most countries. However, a significant question remains in regards to the asymptomatically infected individuals, which may propagate the virus and impede infection control.

The problem To date, initial surveillance has focused primarily on patients with severe disease, and, as such, the full spectrum of the disease. The extent of asymptomatic disease is not clear. Mizumoto et al. mathematical model suggested 17.9-33.3% are asymptomatic carriers. The other question to consider is whether these asymptomatic carriers develop an immune response or continue viral shedding.

SARS-CoV-2, the causative viral agent of the disease COVID-19, is a coronavirus which bears the transmembrane glycoprotein spikes (S protein) typical of viruses in its clade. The spikes on SARS-CoV-2 allows the virus to enter host cells through the human receptor angiotensin converting enzyme 2 (ACE2), present in alveolar epithelial cells. These spikes are a prominent target of human immune responses and have been found to be highly immunogenic and induce antibody production. The receptor-binding domain (RBD) of the S protein is particularly targeted by neutralizing antibodies.

The diagnostic test in symptomatic patients is based on real time polymerase chain reaction (RT-PCR), which tests the existence of specific COVID-19 genes in the sample. However, there are growing numbers of reports of false negative results due to improper sample collection, low viral load or technical instability of the PCR.