# What does the absence of any immune response symptoms mean?

• Medical
It's my (limited) understanding that your immune systems responds to most (all?) microbial threats initially with aches and fever, i.e., that these initial symptoms are not caused by the microbe but by your immune system's activation. So what does it mean if one is infected and infectious but never experiences any symptoms?

TeethWhitener
Gold Member
Your immune system has two main strategies: innate and adaptive. The innate immune system is a general inflammatory response to objects it recognizes to be foreign. This is the origin of aches, fever, etc. Your adaptive immune system is the pathogen-specific response elicited when your body recognizes an invader which it has seen before. If you’re asymptomatic, it generally means your adaptive immune system was able to recognize and fight off the invader before the invader elicited a strong innate immune response which would cause symptoms. Or at least the levels of pathogen in your system remain low enough for your body to clear it before symptoms (which would kick in if the invader were allowed to multiply unchecked).

bhobba, Chris Miller and berkeman
Thanks @TeethWhitener for the informative response. Two grandkids (and a couple of their friends) all tested positive for Covid, but none had any symptoms at all. I wonder where their immune systems learned to recognize the virus.

TeethWhitener
Gold Member
Thanks @TeethWhitener for the informative response. Two grandkids (and a couple of their friends) all tested positive for Covid, but none had any symptoms at all. I wonder where their immune systems learned to recognize the virus.
It very well could be that the virus (for whatever reason) was slow enough in multiplying that the adaptive immune system was able to generate its response (antibodies, killer cells, etc) before the virus got to a level sufficient to cause a high degree of inflammation (aches, fevers, etc). Pathogen-host or microbe-host interactions are wildly complex.

bhobba and Chris Miller
jim mcnamara
Mentor
There are other common cold Coronavirus viruses that are similar and may contribute to immune response. It does not appear to be a major driver for asymptomatic cases.

symbolipoint, Chris Miller and TeethWhitener
atyy
Thanks @TeethWhitener for the informative response. Two grandkids (and a couple of their friends) all tested positive for Covid, but none had any symptoms at all. I wonder where their immune systems learned to recognize the virus.
It's possible they had symptoms, but didn't recognize them. IIRC there was an asymptomatic case (ie. she felt fine) who had an abnormal chest x-ray.

TeethWhitener
@atyy, I've also heard of "happy hypoxia." People with very low O2 levels (like < 60%) but not under any duress. Not sure all 4 kids would feel nothing, no aches or pains or fatigue. Couldn't a simple blood test tell whether it was the adaptive or innate immune system (or neither) that fought off the virus. Wouldn't testing all asymptomatic and mildly symptomatic cases shed some light on the epidemic, as in who's been exposed before (or been misdiagnosed)?

atyy
TeethWhitener
Gold Member
Wouldn't testing all asymptomatic and mildly symptomatic cases shed some light on the epidemic, as in who's been exposed before (or been misdiagnosed)?
Yes. It would also cost a fortune.

jim mcnamara
Mentor
Happy hypoxics are sick, make no mistake. Kind of an unfortunate moniker. SpO2 levels below 94%-95%, depending on who is interpreting, are not considered normal. Pulse oximeters can directly measure hypoxemia.

Happy hypoxics may have SpO2 levels below 90%. What it means is the patient can breathe and speak normally. For a while. Not gasping for air. My understanding: it is taken to mean that hypoxia will probably follow. There are various levels of clinical manifestations or "levels" of Covid disease process. Some physicians view the HH population as usually beginning the descent into more problems.

Here is why --
Simply put: hypoxemia refers to low oxygen content in the blood, and hypoxia means low oxygen supply in bodily tissues. The two are not identical and are defined this way to clarify diagnosis and causation. Hypoxemia untreated leads to hypoxia -- simplified a bit for this discussion. Want more? Look up cyanide or (CO) Carbon Monoxide. Hypoxia exists there without any hypoxemia.

Caveat: My right index finger gives false lows with a pulse oximeter. Finger got mangled in a lawn mower and does not play the game according to the rules. When every other finger reads normally, it shows pulse rate of 30 and SpO2 readings of ~90% and lower. So pulse oximeter readings have limits and require reality checks. I guess my gimped finger is a happy hypoxic...

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atyy and Chris Miller
Yes. It would also cost a fortune.
What bout the pandemic hasn't? Are the antibody tests more expensive than PCR? Sorry, no clue. I just googled, and got $38 for Covid-19 antibody testing at CVS. atyy Science Advisor What bout the pandemic hasn't? Are the antibody tests more expensive than PCR? Sorry, no clue. I just googled, and got$38 for Covid-19 antibody testing at CVS.
It depends on what one is using it for. The UK does antibody tests for surveillance. They sample blood donors (a biased sample), and they also do random sampling. One interesting application is to estimate vaccination rates and infection rates (for the vaccines available in the UK, infection can be distinguished from vaccination as the antibodies produced are different). The UK knows how many people are vaccinated, but they don't know how many people are in the country, and therefore don't know how many are unvaccinated. Their most commonly published estimate for of 93% two-dose vaccination coverage in the elderly uses the NIMS database, which overestimates the UK population, and therefore underestimates the vaccination rate. The NIMS database is useful for medical communication as it contains all the addresses that people may be at, but people may be at more than one address if they moved without informing a local authority. If the ONS database is used, vaccination coverage exceeds 100%, a clear overestimate. The ONS also has a separate method from random serosurveillance which gives an estimate of 98% vaccination coverage in the elderly.

UK blood donor antibody prevalence (p67-70): https://assets.publishing.service.g...000373/Weekly_Flu_and_COVID-19_report_w27.pdf

NIMS vaccination rate estimate (p71, Table 9): https://assets.publishing.service.g...000373/Weekly_Flu_and_COVID-19_report_w27.pdf

ONS serosurveillance vaccination rate estimate (Figure 3): https://www.ons.gov.uk/peoplepopula...ntibodyandvaccinationdatafortheuk/4august2021