In December, the US Centers for Disease Control and Prevention (CDC) reported that scientific evidence led them to reduce the recommended isolation duration for persons with COVID-19 from 10 days to 5. The Centers for Disease Control & Prevention (CDC) reported that the peak periods of SARS-CoV-2 transmission were the first few days of sickness (days 1-3) when the virus was most likely to be spread. There were and still are many scientists that disagree with the conclusion. The other view is supported by several studies showing that many persons infected with COVID-19 remain infectious for at least a week after their symptoms have subsided.
They claim that the reductions in the suggested isolation duration, which are now commonplace across the world, are motivated by politics rather than any comforting new findings. “The realities of how long individuals are infectious have not actually altered,” says Amy Barczak, an infectious-disease expert at Massachusetts General Hospital in Boston. There is insufficient evidence to recommend a shorter period of isolation (5-10 days). According to data provided by Barczak on the medRxiv preprint service, 25% of SARS-CoV-2 Omicron variant-infected individuals may be contagious for up to eight days after the first infection. The issue of how long a person with COVID-19 remains contagious may seem straightforward, but scientists warn that the answer is more nuanced than it seems.
Benjamin Meyer, a virologist at the University of Geneva in Switzerland, explains that while “we always conceive of it as a black-and-white issue… if somebody is infectious or not contagious,” in reality, it is a numbers game and a likelihood. Indeed, the rules and starting points of this numerical game are always changing. Meyer states that when someone stops being infectious is determined by how rapidly the virus is cleared from their system, which may be affected by factors such as emerging variations, vaccination, and variable degrees of innate immunity triggered by past infection. Factors associated with behaviour are also significant. According to his research, the intensity of a person’s symptoms is correlated with the likelihood that they may spread their illness to others since people who are sick prefer to avoid social interaction.
A majority of experts agree that PCR tests can show a positive result long after an infected person is no longer contagious. The tests, which look for viral RNA, may pick up inert particles that remain after the majority of the active virus has been eradicated. Lateral flow (or ‘rapid antigen’) assays, on the other hand, provide a more accurate indicator of infectiousness since they identify viral proteins only when the virus is actively reproducing. Emily Bruce, a microbiologist & molecular geneticist at the University of Vermont in Burlington, says, “There are still all these things that we’re not exactly sure about, but if I had to sum it up in one very concise message, it would be that if you’re antigen positive, you shouldn’t go out and interact closely with people who you don’t want to be infected.”
What about someone who has had a negative lateral flow test for a few days but still has a high temperature and a severe cough? Bruce stresses the significance of keeping in mind that despite appearances, persistent symptoms do not always point to ongoing contagiousness. A person “may undoubtedly experience symptoms for longer than they test positive on lateral flow,” she says. In my opinion, this is because the immune system, rather than the virus, is to blame for many of the symptoms.
Verification of Transmission
The elimination of free lateral flow testing occurred at the same time as isolation standards were loosened in several nations, such as the United Kingdom. Scientists have been specifically looking at how many persons with COVID-19 are likely to stay infectious after this time, as it is assumed that many people who follow the new recommendations will stop isolating after five days without testing. Researchers rely on proxy measurements to estimate when people should stop being infectious because it is impractical to follow the direct forward transmission of the virus from large numbers of people and evaluate how it declines over time. For this purpose, researchers like Barczak, who have access to a high-security biosafety level 3 laboratory, can conduct studies to determine whether or not live SARS-CoV-2 can be cultivated from samples obtained from patients over the course of several consecutive days.
She explains, “If you’re still releasing a virus that we can culture out of your nose, there’s at least a high possibility you’re still contagious to other people.” Barczak notes that as new strains have arisen and different labs have conducted these tests, a general agreement has developed that it is extremely rare for humans to shed culturable virus after ten days. As a result, she explains, “it is quite uncommon for someone to remain contagious beyond 10 days.” Still other research abstracts from the real world by inferring someone’s infectiousness from their viral RNA levels as determined by polymerase chain reaction (PCR) tests.
It’s now much less of a hassle to deal with massive data sets. For instance, over 700 participants’ symptom onset dates can be used in PCR testing for research coordinated by the Crick Institute and University College Hospital in London. Research including this cohort reveals that even after seven to ten days, a sizeable proportion of individuals retain viral levels high enough to initiate further transmission. This holds true regardless of the type of variation or the number of vaccination doses administered. The research paper was posted to the medRxiv preprint server on July 10.
David LV Bauer, a virologist at the Crick Institute and co-investigator on the study, says, “We’re not measuring live virus, but there is now a vast amount of work in the literature that offers a very solid mapping of what constitutes a viral load likely to create an infectious virus.” Although this isn’t an ideal scenario, it’s not far off, either.