key: cord-270805-o6rbfmie
authors: Hussein, Osama
title: Second wave of of Covid-19 is determined by immune mechanism
date: 2020-09-02
journal: Med Hypotheses
DOI: 10.1016/j.mehy.2020.110238
sha: 
doc_id: 270805
cord_uid: o6rbfmie

A second wave of new severe acute respiratory syndrome coronavirus 2 (Covid-19) cases is widely feared. In fact resurgence of cases has been clearly observed in several countries that had seen flattening of the epidemic curve. In general, relaxation of community control measures is almost always blamed for the resurgence of cases. In this letter, the author describes an immunological explanation for the double-peaked epidemic curve of new viral diseases including Covid-19. According to this hypothesis, a second wave of cases is due to the effective innate immunity in some of the population. These individuals may later develop clinical disease upon repeated exposure. This theory claims that a double-peaked pattern of new cases in a new viral epidemic is intrinsically determined by the pattern of pathogen interaction with the host. According to this hypothesis, relaxation of the community control measures is not responsible; at least in part, for resurgence of cases.

countries. In Japan, a crisp two-peak incidence curve is clear(2). Similar trends are reported from other countries.

The notion of epidemics that normally have two peaks of new cases over time is widely accepted(3); although epidemiologists have not characterized this pattern as an established model. In general, the resumption of international travel or the relaxation of the community control measures are are almost always blamed for the resurgence of the disease incidence.

In this letter, this author suggests that a double-peaked epidemic curve is an intrinsic feature of viral outbreaks. According to this hypothesis, immune response to virus exposure in different individuals determines the spread pattern in the community.

The two principal divisions of the immune response to pathogens are the innate and the adaptive immunity. Both divisions play a major role in the body response to viral exposure. Together with the development of clonal virus-specific CD8 + T lymphocytes, these individuals will experience subclinical or clinical viral illness and are responsible for the early rise in the epidemic curve.

Assuming the above hypothesis is true; a viral epidemic curve will show an early upstroke corresponding to persons who pass into viremia upon initial exposure to the virus followed by a second slower rise due to cases who develop the disease after repeated process of inoculation and clearance at the point of entry. It is fairly reasonable to assume that the latter group of patients may be the healthier individuals who will have lower case-fatality rate. Together with the notion of the covid-19 cases getting milder with time, objective evidence from Japan indicates that the second peak in incidence is not accompanied with a corresponding peak in fatality.

The implications of this hypothesis are medically and socially relevant. According to this theory, resurgence of a viral outbreak is intrinsically determined by the nature of the virus interaction with the host. Relaxation of the community measures or "reopening" of the economy may not be blamed for a second rise in incidence rates. The theory also provides one explanation for the possible observation of decreased case-fatality over time.

In conclusion, the author describes an immunological explanation for a double-peaked epidemic curve of Covid-19 and other new viral diseases.

E64-E7. 2. WHO coronavirus disease (COVID-19) dashboard. Geneva: World health organization

Beware of the second wave of COVID-19

Pathogen Recognition and Innate Immunity

Activation and evasion of type I interferon responses by SARS-CoV-2

Human Cell Tropism and Innate Immune System Interactions of Human Respiratory Coronavirus EMC Compared to Those of Severe Acute Respiratory Syndrome Coronavirus

The author has no potential conflict of interest to declare.
