Six months into the COVID-19 global pandemic and many questions still remain unanswered concerning the nature of this novel coronavirus. Perhaps one of the most important unresolved mysteries surrounds human immune responses to the virus and how long a person may be resistant to SARS-CoV-2 following recovery from an initial infection.

A new study, published in the peer-reviewed journal Nature Medicine, has found antibody levels in subjects suffering from asymptomatic infections dropped significantly when measured two months after hospital discharge. While this does not at all mean these subjects are prone to reinfection, the study suggests it does affirm how little we know about long-term antibody-mediated immunity.

The researchers were evaluating immunity by measuring blood levels of two types of immune system antibodies: Immunoglobulin G (IgG) and neutralizing antibodies.

The study found striking drops in IgG levels for both symptomatic and asymptomatic cases in the eight weeks following hospital discharge. On average, IgG levels dropped 76.2 percent in symptomatic cases, and 71.1 percent in asymptomatic cases.

More significantly, IgG levels were generally higher at all phases of the disease in symptomatic cases compared to asymptomatic cases, and by the eight-week follow-up point 40 percent of asymptomatic cases registered no detectable levels of IgG in their blood.

Things looked slightly better on the neutralizing antibody front despite drops in levels detected in both symptomatic and asymptomatic cases. On average, asymptomatic cases saw a 8.3-percent drop in neutralizing antibody levels at the eight-week followup, compared to a 11.7-percent drop in symptomatic patient levels.

As we literally only have a few months of data illustrating how this new virus interacts with the human immune system it is profoundly unclear whether these drops in antibody levels mean a person is more susceptible to reinfection. The study does reference prior work tracking these same antibody levels in SARS and MERS patients, suggesting survivors of those infections did not show this kind of rapid antibody level reduction.

https://newatlas.com/health-wellbeing/covid19-immunity-antibody-asymptomatic-coronavirus-resistance-duration/

thanx, read that

> antibody levels in subjects suffering from asymptomatic infections dropped significantly when measured two months after hospital discharge

OK. Keep in mind that one virus can generate a range of antibodies, and not all people have the same suite of antibodies.

> The researchers were evaluating immunity by measuring blood levels of two types of immune system antibodies: Immunoglobulin G (IgG) and neutralizing antibodies.

Good. They have taken that into account.

An early study in Korea (from late March IIRC) showed that reinfection occurred even for those who weren’t asymptomatic, and within a month or so. These findings were later questioned (some thought the reinfection was just a mistaken identification of broken-down viruses from the first infection). But I’m inclined to believe the original conclusion, that reinfection occurred.

However, and here I’m going out on a limb a bit, I suspect that reinfection is less severe than original infection.

I’ve been reinfected by my own cold once since lockdown, where I gave the virus to mrs m and she reinfected me. But the reinfection was noticeably milder than the first infection.