Does recovering from Covid 19 cause immunity to new infection by Sars Cov2 ?

The WHO warns that it is not proven that we acquire immunity to Sars Cov2. If we don’t we are pretty much doomed. However, I don’t see how people could recover without developing immunity or develope immunity without memory with human immune systems. Here, as often, the burden of proof is placed on the optimistic hypothesis. Here again (third time) I dare to be optimistic (third time’s a charm).

At Daily Kos Mark Sumner has an excellent post on the topic. I cut and pasted my comment below. I agree with everything he wrote except the part about the common cold (which is a syndrome caused by one of dozens or hundreds of diffferent known viruses). In particular a key open question is whether all people who recover are immune but some are more immune than others (as he notes it is known that some have low anti Sars Cov2 antibody levels). Also it isn’t known if and when there will be new strains which evade the currently existing neutralizing antibodies.

His post is brief and too good to excerpt. Just click this link (then come back to read my post or not — it’s not at the same level)

First there is strong evidence that exposure to Covid causes people to make neutralizing antibodies, you mention this.  Here is my first google hit  .  In that article, the cell making such an antibody was immortalized by fusion with a leukemic cell and so there is a neutralizing monoclonal which can, in principal, be mass produced and used as a treatment.   The problem (as usual) is that it isn’t proven that it works and such proof takes a lot of time and money.

I don’t think there are viruses which infect us again and again.  We are infected by new viruses (here I include mutants of the old virus as in seasonal flu). The common cold is a syndrome not a virus. There are dozens to hundreds of known viruses which cause colds (with similar symptoms).  By your definition we get many different viral diseases with similar symptoms.

There is certainly a risk that Sars Cov2 will mutate in a way such that it is no longer neutralized by currently neutralizing antibodies,   and so there will be a new epidemic even if enough people are vaccinated to provide herd immunity to Sars Cov2 1.0 (influenza does this which is why there is seasonal flu).  It is also possible that this won’t happen (there wasn’t a smallpox 2.0 which infected people who were vaccinated).

Importantly, antisera against Sars Cov2 can be tested (in cell culture) against isolates from different continents.  So far, I think, the evidence is that sera (polyclonal) antibodies which block one strain block all existing strains (which sure doesn’t mean all strains which will ever exist).  There is a vaccine (good old fashioned killed virus vaccine, which has protected Rhesus macaques from infection by Sars Cov2 squirted in their lungs b
If our immune system can’t stop Sars Cov2, then how to people recover ? Why has anyone gone from positive to negative ?

Again, we don’t get the same common cold virus again and again.  There are many different cold viruses.  Most are picornaviruses (double stranded circular RNA genome, small, like polio) some are coronaviruses, and some are adenoviruses (which cause fierce colds).

I think the WHO is putting the burden of proof on the hypothesis that, whatever happens in us to beat one Sars Cov2 infection lasts for a while.  If this were not true, it would be unique (I think).

update: there is now more direct evidence in a non peer reviewed preprint here

Neutralizing antibody responses to SARS-CoV-2 in a COVID-19 recovered patient cohort and their implications
Fan Wu, Aojie Wang, Mei Liu, Qimin Wang, Jun Chen, Shuai Xia, Yun Ling, Yuling Zhang, Jingna Xun, Lu Lu, Shibo Jiang, Hongzhou Lu, Yumei Wen, Jinghe Huang

“neutralizing antibodies (NAbs)”

Plasma collected from 175 COVID-19 recovered patients with mild symptoms were screened using a safe and sensitive pseudotyped-lentiviral-vector-based neutralization assay. [skip]
SARS-CoV-2-specific NAbs were detected in patients from day 10-15 after the onset of the disease and remained thereafter. [skip]
Notably, among these patients, there were ten patients whose NAb titers were under the detectable level of our assay (ID50: < 40)

So according to We et al 165 out of 175 people had produced antibodies which prevent infection of cells. So this is evidence that people recover because of acquired immunity. On the other hand, not all subjects had measurable quantities of the antibodies (and the measure is what dilution blocks virus entry). So an exposed and immune passport would be unreliable — those 10 people are assessed as still vulnerable. This isn’t the end of humanity (165/175 is enough for herd immunity to get R under 1). But it matters for policy (as WHO insisted). Also “remained thereafter” doesn’t mean forever. It can only mean up until now which is, at most, months after the recovery (even if the blood was collected as soon as some people had recovered).

Good news.