Covid, controversy in the US for the reduction of isolation to 5 days without a negativity test. According to the latest studies, the infectivity of a person infected with Omicron lasts an average of 9 days, although it depends on an individual’s level of immunity.
In Italy, the quarantine rules for people who have come into close contact with a positive person have just changed: from now on for the unvaccinated (or who have only undergone the primary vaccination course for more than 120 days) are expected 5 days instead of 10. The provision applies to asymptomatic people. The termination of quarantine conditioned by the negative outcome of a final rapid or molecular test. Furthermore, it is mandatory to wear the Ffp2 masks also for the following 5 days. As was already foreseen by a previous circular dated 31 December last, the provisions remain unchanged for those who have full vaccination coverage and have also taken the booster dose (or been vaccinated / cured in the last 120 days): 5-day self-monitoring and obligation to wear the Fffp2 mask for 10 days. Always in the absence of symptoms and without negative buffer output.
Isolation of positives
Currently in Italy the positives must instead however, isolate yourself for 10 days with a final negative buffer, regardless of their vaccination status. Recall that isolation is the measure that applies to positive cases and quarantine that which concerns the close contacts of a positive case.
The period of isolation for people who tested positive for Covid-19, it was recently reduced 10 to 7 days in England (in the presence of two negative rapid tests on days 6 and 7) and some officials asked to align with the choice of the US which reduced the isolation to only 5 days.
In USA isolation for 5 days with no final test
In fact, at the end of December i Centers for Disease Control and Prevention Usa made this decision: 5 days of isolation for asymptomatic infected Americans and end of period without negative test (only asked to wear a mask outside for another five days after leaving the isolation).
But what scientific evidence supports the decisions on reducing quarantine and isolation? The heated debate between scientists and governments: in the US the CDC have been blamed to have issued recommendations based on insufficient evidence. Many have pointed out that scientific data supporting a shorter isolation period for Omicron infections is scarce. Critics have complained that the virus could spread further as infectious people are allowed to return to offices and schools. When the director of the US agency, Dr. Rochelle P. Walensky, defended herself by citing a scientific review of dozens of articles analyzing coronavirus infectivity, she was pointed out that many of them were based on variants other than Omicron.
Average of the infectious period 8-10 days
What do we know so far of the Omicron infectious period? It seems that it can begin a day or two before the onset of symptoms, in asymptomatic patients 48 hours before the positive swab are calculated. It is estimated that the infectious period
last from 8 to 10 days in moderate cases and on average up to two weeks in severe cases, but infectivity generally subsides 7 days after the onset of symptoms. In vaccinated with 2 or 3 doses, a shorter duration of symptoms is observed and therefore, it is assumed, also of the ability to infect others. The variables, however, depend on an individual’s level of immunity and on the properties of the variant itself. Some people remain contagious for much longer than others and rapid test evidence suggests that some patients are still infectious even after 5 days.
Japanese study: virus peak from the third to the sixth day
Two recent studies take stock of this aspect: the first, released on January 5 by the Japanese National Institute of Infectious Diseases, highlights how patients with the Omicron variant shed the virus longer after symptoms appear. The amount of viral RNA resulted highest 3 to 6 days after diagnosis (or the onset of symptoms). Previous studies of other variants showed a peak of transmission between 2 days before the onset of symptoms and 3 days after. The Japanese study suggests that with Omicron, the virus’ peak spread should be shifted forward by 2 to 3 days, with a marked decrease in virus detectable 10 days after diagnosis or onset of symptoms. In fact, no infectious viruses in the respiratory samples were detected 10 days after diagnosis.
Harvard study: duration of 9.87 days
The second job published in pre-press (and therefore without revision) on 14 January by the Harvard TH Chan School of Public Health of Boston. The team quantified the duration of viral proliferation of individuals with acute Omicron and Delta SARS-CoV-2 infections. Of the 27 Omicron-infected subjects who tested positive on day 1 from the risk contact, 52% were positive by PCR (molecular swab) on day 5, 25% on day 6, and 13% on day 7 after detection. Of the 70 Omicron-infected individuals detected from day 2 after a previous negative or inconclusive test, 39.1% were PCR positive on day 5, 33.3% on day 6, and 22.2% on day 7 after detection. Overall, the Omicron infections had a mean duration of 9.87 dayshowever, slightly less than Delta infections of 10.9 days, but more than the 5 days required by the new CDC regulation.
Prudence required
After evaluating the scientific data on Omicron’s viral shedding, caution with respect to isolation (and quarantine) is a must: even the authors of the last cited study write that the substantial fraction of individuals with detectable positive values at 5 days of infection underlines L’heterogeneity of the infectious periodwith implications for isolation policies.
February 6, 2022 (change February 6, 2022 | 11:57)
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