The Rise and Fall of Antibodies in Mild and Asymptomatic COVID-19

A preprint study in biorxiv shows that not all who have asymptomatic and mild Covid-19  develop protective antibodies developed against  COVID-19.

As a brief background, after exposure to a virus or bacteria, whether natural or by vaccination, the immunoglobulin M (IgM) rises, followed by immunoglobulin G (IgG). Immunoglobulin is the technical term for the antibody that is used in the biological sciences.

The immunoglobulins are made by an immune cell called  B cells. The previous exposure to a germ allowed the B-cells to make a “template” for an immunoglobulin for that specific microbe.  

If exposed a second time, the production of antibodies will be much faster, and the infection will not be allowed to progress.

With that background, let’s dive into the study.

Antibody dynamics to SARS-CoV-2 in Asymptomatic and Mild COVID-19 patients

The study was done by a collaboration of several institutions in Wuhan, China. On April 8, 2020, the lockdown in Wuhan was lifted. To ensure safety, people returning to work were screened for the presence of COVID-19.

All were screened for the presence of COVID-19 by nucleic acid testing (NAT) using nasal and throat swabs. The blood was also tested for IgG and IgM.

All were followed and tested repeatedly for 65 days.

This article will report on asymptomatic and mild cases.

Asymptomatic cases do not have any symptoms but are tested positive on their swab or antibody test.

Mild cases have respiratory symptoms like cough, fever, or sore throat and have no changes in lung imaging (x-ray) but tested positive on their swab and/or antibody.

They studied 63 healthy contacts, 63 asymptomatic individuals, and 51 patients with mild COVID-19.

Results

Asymptomatic Cases

1. 81% of asymptomatic cases are swab (-) and antibody (+).
2. 12.3% are swab (+) and antibody (+).
3. 6.3% are swab (+) and antibody (-). 
4. In asymptomatic individuals who will develop antibodies (63.5%), the IgM and IgG went up as early as the seventh day after exposure and peaked from 17 to 25 days. After which, they both declined. After two months, the IgM and IgG in asymptomatic cases cannot be detected.

Mild Cases of COVID-19

1. 60.3% are swab (+) and antibody (+)
2. 25.4% are swab (-) and antibody (+)
3. 11.3% are swab (+) and antibody (-)
4. Mild patients have antibodies from 1 day after symptom onset and persisted until 29 days after symptom onset. However, 11.8% did not produce any antibodies.

Mild cases also have higher levels of antibodies than asymptomatic cases and healthy contacts. Their antibodies lasted for at least 65 days. It could have been longer, but the duration of the study is only 65 days.

These results are consistent with another preprint study from Montreal, Canada, that showed a significant decline of IgM and IgG between 6 and ten weeks after the symptom onset.

What do the results mean?

These findings are significant because 81% of asymptomatic people with COVID-19 will test negative for the SARS-CoV-2 nucleic acid if only the swab is done. To find them, antibody testing will be needed.

After 2 months, asymptomatic cases will no longer have protective IgG against COVID-19.

85.7 % of people who had mild symptoms will have antibodies for at least 65 days.

In a previous article, Protective Antibodies Against Coronaviruses are Short-Lived, two studies showed that protective antibodies against coronaviruses, including SARS-CoV-2, only last for 6 months.

The findings have repercussions because that means that herd immunity may not happen. Herd immunity is where 70% of the population will have resistance against COVID-19. Once 70% have protective antibodies, the spread of the virus will be slowed down.

This study shows that not all who are infected develop antibodies.

The second is that “immunity passports” or “risk-free certificates” will not happen.

“Immunity passport” is a concept wherein a person who is previously infected with COVID-19 can go anywhere showing documentation or a “passport” that they already have antibodies in their system.

The third is that vaccinations may not be that effective.

The fourth is based on the Canadian study. Blood from recovering COVID-19 patients, also known as convalescent plasma, should be used right away before six weeks of the donor’s symptoms onset to maintain its effectiveness.

Currently, the only thing to protect against COVID-19 to minimize the risk with a healthy lifestyle and strengthen the immune system.

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

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