The Total number of COVID-19 is much Higher

Posted on by Jesse Santiano, M.D.

As of date, the total number of COVID-19 cases worldwide is more than 12 million. COVID-19 is most commonly detected with a nasal or throat swab.

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Johns Hopkins Global COVID-19 Cases and Deaths

If there are enough SARS-CoV-2 viral particles that are in the lining of the nose or the throat, then the test becomes positive. However, after a few weeks, the viral particles become undetected.

Another way to detect people who had COVID-19 is to check for antibodies for COVID-19 in the blood. The antibodies detected in this manner are immunoglobulin M (IgM) and immunoglobulin G (IgG). The IgM is initially produced, and then the IgG comes later.

Another antibody that is lesser known is called immunoglobulin A (IgA). IgA is the most abundant type of antibody in the body. Comprising 70% of all antibodies.

They are found in body secretions of the respiratory, genitourinary, and prostate. They can be detected on tears, saliva, and breast milk.

The mucosa is the inner linings of the respiratory tract and other organ systems that communicate with the world outside the body.

The IgA works as the first-line defense against germs like the SARS-CoV-2, the virus that causes COVID-19.

Research from the University Hospital in Zurich Switzerland looked for the presence of mucosal IgA in people with mild COVID-19. That study is published as a preprint on biorxiv.

What they found is that in mild COVID-19, the IgA rise only for several days in the respiratory tract. The IgA were able to stop the multiplication of the SARS-CoV-2 virus, which explains why the symptoms stayed mild, and they have a faster recovery.

Since the course of the COVID-19 was mild, no IGA and IgG were detectable in the blood since there was no need for them. The same people may also test negative with the usual nasal or throat swab since the number of virus particles may be too small to be detected.

Based on that, there is a large group of people out there who already had COVID-19 whose symptoms are mild that they did not qualify for testing or were not tested. That same group of people will also test negative for antibodies in their blood.

Onur Boyman, professor at the Department of Immunology at the University Hospital in Zurich and also the director of this study, he said,

“The current antibody tests do not cover all cases by a long way,”  The number of infections might even exceed five times the known figures.

Age Differences in Mucosal IgA Production

More mucosal IgA is found in the younger age groups compared to the older population. This explains why the elderly tend to develop worse COVID-19 and have high mortality.

This could also be the reason as speculated by the study authors on why the younger age groups tend to be asymptomatic and have mild symptoms.

Does Mucosal IgA Confer Long-Standing Immunity?

At this time, we don’t know how long is the protection of mucosal IgA. We don’t know yet if the IgA will also be as protective in future COVID-19 exposures. More studies are needed.

At his time since we know that the COVID-19 antibodies only last for a few months, it is essential to lower the risk of getting severe COVID-19 with adequate blood pressure and blood sugar control among the hypertensives and diabetics respectively.

Knowledge about Covid-19 is rapidly evolving. Information may update as new researches are done. Stay current by subscribing.

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Reference:

Boyman et al. Systemic and mucosal antibody secretion specific to SARS-CoV-2 during mild versus severe COVID-19. bioRxiv 2020.05.21.108308; doi: https://doi.org/10.1101/2020.05.21.108308

 

 

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