Most Covid transmission ‘asymptomatic’

The following is an excerpt from MedPage Today.

A significant proportion of Covid-19 transmission is asymptomatic or pre-symptomatic — potentially as high as 60%, according to a 2021 JAMA Network Open modeling study.

That may be even higher now, as early reports have signaled a greater percentage of asymptomatic infections from Omicron than from previous variants.

That could have a lot to do with higher baseline levels of immunity in the population when that variant hit, Helen Chu, MD, MPH, an infectious diseases physician at the University of Washington School of Medicine, told MedPage Today.

Chu said the more exposure to Covid-19 that an individual has — either in terms of prior infection or vaccination — the broader the immunity and the better the ability to control the virus. In such cases, an individual is more likely to be asymptomatic or have mild symptoms, she said.

Estimates of asymptomatic disease rates with Covid-19 — the proportion who are infected but never manifest symptoms — have ranged from about 25% to 40% throughout the pandemic, with a number of papers, including one in the Annals of Internal Medicine, coming in at about a third of cases.

There are no data yet on whether Omicron’s subvariants, such as BA.2 and BA.4 and BA.5, cause more asymptomatic infections, Otto Yang, MD, an infectious diseases physician at the David Geffen School of Medicine at UCLA, told MedPage Today.

But he also noted that high levels of population immunity puts the U.S. in a “completely different situation from earlier when there weren’t vaccines and few people had been infected.” (Continued)

Read full article here.

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6 thoughts on “Most Covid transmission ‘asymptomatic’”

  1. There are several concerns with the MedPage article:

    – The studies it relies on are more than a year old, meaning the data would reflect the impact of Covid prior to the emergence of Omicron and its subvariants, which are now dominant. That brings the relevance of these findings into serious question.
    – There are always legitimate questions about model-based studies, as the modeling assumptions can be incorrect. This is especially true for the JAMA model-based study published in Jan 2021 which means it has no information from all of 2021 and beyond. This should at least be updated, but there is no reference to any such update. Without updated information this is a very outdated model and possibly irrelevant to the current medical situation in May 2022.
    – There is a legitimate question about the impact/severity of Covid contracted from someone who is asymptomatic. If there is no medical impact – i.e. if contracting Covid from someone asymptomatic results in asymptomatic Covid, then what is the public health threat? This question is not addressed at all.
    – Statements are made about the possibility of long-term health effects from asymptomatic Covid but no evidence is presented to support this possibility. It appears to be pure speculation.

    Taking these concerns together it would appear that this article is intended to reinvigorate the narrative that masks and lockdowns are again needed, based on very questionable information. It looks like another attempt to drive a particular policy. Thank you for bringing this to everyone’s attention, it shows that there is still a desire by some to re-institute those policies, and the continued need to strive for accurate information on Covid.

  2. I am suspicious of studies that rely on “models” — it means it isn’t from the real world. It all depends on the assumptions that were made to put in the model. Might be good, might be poor. For the same reason I discount a lot of climate science. Models, models, more models. The climate is so complex, it is impossible to accurately model it. Biology is even more complex.

  3. Thank you to both Mark and Eric; I agree with their comments.

    This emphasis on “asymptomatic transmission” makes me wonder if there is a push to re-define illness. Instead of waiting for symptoms, signifying the body’s attempt to deal with an infection, in order to determine a person is sick and can communicate the infection to others, are we now relying on tests? If so, the tests become the rationale for lockdowns for everyone–instead of recommending isolation for those who are clearly ill.
    Anyone who looked at the high cycling thresholds used with the PCR tests early (still?) in the covid pandemic knows how inaccurate–and easily manipulated–test results can be.

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