My understanding is that the experts are still undecided on whether or not a person who already got infected (and recovered) might get it a second time.
It seems to me that if it were possible to get it a second time, we would have heard of such a case by now. But I have not heard of such a case. It therefore seems likely that getting the virus does give one an immunity, at least for a while.
Is my logic reasonable? Any other thoughts?
We have no idea which people have had it. Even without trying you could imagine a person who got it twice and they were asymptomatic the first time and didn’t get a test and then they got a test the second time. Further their have been unconfirmed reports of people who have tested positive twice with a negative test in the middle. It doesn’t seem to happen very often but the dearth of testing here in the Us makes it very unlikely we could catch a person who has it twice unless they are hospitalized both times.
There have been reports of people cleared of the virus testing positive again. Whether that’s because of a poor clearing process, sloppy testing, or the ability to become reinfected we don’t know yet.
There are fairly few germs that are impossible to get twice. Even second primary chickenpox cases happen sometimes. Odds are it can happen. The question is how often, if it becomes often with time, how much time, and if a second case is it less severe and/or contagious if it occurs?
Similar questions will be asked about vaccination, if when it happens, which rarely is complete protection.
The reports of people with successive antigen testing indicating positive/negative/positive can very likely be attributed to a combination of false negatives and the fact that the antigen test amplifies fragments of RNA that are identified part of the viral genome. The problem with the former is that there is an estimated 30% false negative rate from the CDC test, and the later is that viral RNA fragments may persist in the blood serum for weeks or months after infection since they are inert. There is no evidence that I’ve found that someone has demonstrated a significant presentation of COVID-19, recovered completely, and then presented again.
If SARS-CoV-2 is like other coronaviruses in general we can expect to see at least many months of effective immune response, although it would be wise to act as if this were not the case even if you have had a positive antigen test because there is a lot about the virus that is not understood. There are several antibody test available now developed in different countries although many seem to have been deployed without much validation, and some are reported as showing negative antibodies on patients who were positively identified as infected. This does not necessarily mean the test does not work or that the patient will not have effective immunity; it is possible for someone to have become infected, developed an adaptive immune response, and then cleared the antibodies but still have somatic hypermutation of memory B-cells which will still provide a rapid immune response even though antibodies are not initially present.
However, response to infection from this virus is so varied, with many people presenting little or no symptoms and a minority of patients having serious or life-threatening reactions that appear to be due to a severe agglumation response, that it is hard to say how widely immunity from exposure will vary from person to person. And unlike a disease like measles or chickenpox that has a consistent response and results in essentially lifelong immunity, most of the coronaviruses that infect humans can reinfect after some period of time. This presents a challenge for researchers trying to produce a vaccine, too. One of the most hyped efforts — the Moderna mRNA vaccine which has pledged to have a candidate in trials by the end of summer and able to start producing vaccine by the beginning of next year — is presumed effective on the ability to stimulate immune response by replicating portions of the viral genome associated with the spike protein to the immune system (delivered by different vectors).
It is unknown how effective a mediated immune response to the mRNA fragment will actually be, so despite the promotion of this vaccine as a near term silver bullet, all other promising efforts toward more conventional vaccines should be pursued as well until one of them demonstrates safe and long lasting protection across the entire population.
Stranger
I had chickenpox twice, first time when I was around six and again around eleven.
My family doctor didn’t believe me when I said I’d already had it, until I showed him the pox mark I got the first time on my temple.
Thanks, all. That’s what I figured.