SARS- CoV-2, also known as the Covid- 19 virus, causes an acute respiratory infectious disease. Humans are generally susceptible. The main source of infection is currently people infected with the virus, even those who have an asymptomatic course. According to recent epidemiological studies, the incubation period varies from 1 to 14 days, but most commonly from 3 to 7 days. Typical symptoms at manifestation include fever, fatigue, and dry cough. Among others, rhinorrhea, sore throat, myalgias & diarrhea symptoms may occur in rare cases.
Pandemic can only be contained by interrupting the transmission of infection. Considering that most transmission is caused by asymptomatic virus carriers, systematic and repeated screening of the population has a very special role. Without screening, we deprive ourselves of the opportunity to prevent further de-escalation.
Symptomatic and Asymptomatic Virus Carrier
A study of 303 SARS-CoV-2 patients (89 of whom were persistently symptom-free), symptomatic and asymptomatic infected individuals had similar Ct values in PCR during the course, meaning they released comparable amounts of viral RNA.¹ In another study published on behalf of the British Geriatric Society, the authors concluded that systematic prevalence testing is needed, particularly in the nursing home sector, to reduce the risk of transmission by asymptomatic carriers and to manage outbreaks in this setting. ² Asymptomatic SARS-CoV-2 virus carriers have a similar viral load to symptomatic patients. Therefore, isolation of infectious individuals must occur regardless of signs of illness. Screening is used to ensure this, or to move one step closer to this goal, which has not seemed feasible until now due to the insufficient area-wide capacity of PCR testing.
Immunity against SARS-CoV-2
There is concern that, similar to natural COVID-19 infection, the vaccine may not elicit a long-lasting immune response and reinfection may occur. It has been reported that natural immunity to coronaviruses leading to mild or moderate infection may last only a few months after illness. Thus, while antibody responses in most individuals infected with SARS-CoV-2 resolve within weeks of infection, the magnitude of the neutralizing antibody response in asymptomatic individuals is not only less, but also declines more rapidly than in symptomatic individuals. 3
There are two main methods for detecting serum antibodies to SARS-CoV-2. Enzyme-linked immunosorbent assay (ELISA), a laboratory method for quantitative antibody detection, is an established method but has a long turnaround time and high cost. Immunochromatographic lateral flow assays (LFA), on the other hand, can be used as point-of-care (POC) assays and typically provide results within minutes, but the results are qualitative and not quantitative. Therefore, POC assays that detect serum antibodies to SARS-CoV-2 may be necessary as an adjunct to ELISA-based techniques, particularly to monitor the population-based prevalence of immunity.
Carefully selected serological POC tests for SARS-CoV-2 can be used in large-scale testing, but should only be used by licensed medical personnel capable of understanding their limitations and interpreting the results.
1. Lee S, Kim T, Lee E, et al. Clinical Course and Molecular Viral Shedding Among Asymptomatic and Symptomatic Patients With SARS-CoV-2 Infection in a Community Treatment Center in the Republic of Korea. JAMA Intern Med. Published online August 06, 2020. doi:10.1001/jamainternmed.2020.3862
2. Sean P Kennelly, Adam H Dyer, Claire Noonan, Ruth Martin, Siobhan M Kennelly, Alan Martin, Desmond O’Neill, Aoife Fallon, Asymptomatic carriage rates and case-fatality of SARS-CoV-2 infection in residents and staff in Irish nursing homes, Age and Ageing, , afaa220,
3. Jeyanathan M, Afkhami S, Smaill F, Miller MS, Lichty BD, Xing Z. Immunological considerations for COVID-19 vaccine strategies. Nat Rev Immunol. 2020;20(10):615-632. doi:10.1038/s41577-020-00434-6