The asymptomatic, those who have Covid but cannot be seen because they do not even have a timid rise in fever, do not manifest a sneeze or a cough, are as dangerous as full-blown Covid patients. This is supported by a systematic review, and meta-analysis, published in Jama (journal of the American Medical Association) by a group of Chinese authors. Through the search in the database, 2,860 studies were identified that have as their subject the percentage of asymptomatic SARS CoV-2 infections in people tested and in those in whom the presence of the virus has been confirmed. The first conclusion to which the research has led is in some ways a recommendation: “Asymptomatic infections – explain the authors – should be managed in a similar way to that of confirmed infections, including isolation and the search for people who have come into contact with the asymptomatic “. Framework that the new Omicron variant has strengthened, given the high contagiousness it brings with it.
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100 million confirmed cases
Covid-19 officially appeared for the first time in December 2019. Around the world, 276,436,619 confirmed cases have been registered so far, with 5.374.744 deaths (WHO data as of December 23). A disease whose course varies: from mild asymptomatic respiratory infections to pneumonia, to arrive at acute respiratory distress syndrome. In this regard, patients who had no symptoms at the time of the systematic review screening were defined as “having asymptomatic infections”. Definition that includes those who had not yet developed symptoms, but would have accused them later (presymptomatic infections), as well as people infected, but who would never have had a symptom (true asymptomatic or hidden infections). A condition, that of the asymptomatic, very similar to a gamble, because it leads those concerned not to seek medical care and not even to measure their temperature as a precaution. Ultimately, only thorough testing and close contact tracking could uncover asymptomatic infections. Because, unlike Sars, which had little known transmission from asymptomatic patients, the facts have shown that the latter are a potential source of transmission of Covid-19.
Asymptomatic, dangerous in the family, hospitals and communities
But when can an asymptomatic be really dangerous in terms of the likelihood of contagion? The highest Covid viral load in throat swabs was found at the time of symptom onset, indicating that infectivity had peaked during or before they came out covered. Furthermore, studies have shown that asymptomatic infections may have contributed to the transmission of the virus in families, nursing facilities and cluster formation.
Given that, precisely because in recent months the pandemic had been contained, in many countries and regions, travel restrictions had been lifted and public places reopened, thus favoring the “hidden” circulation of the virus.
“Asymptomatic infections should be considered a source of Covid-19 infections that plays an important role in the spread of the virus within the community, just as public life gradually returns to normal – the researchers clarify -. The management of asymptomatic carriers thus proves essential to prevent cluster outbreaks and transmission within the places of social contact “. However, until now, a complete assessment of the percentage of asymptomatic infections between the tested and confirmed populations, in fact, was not there.
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The meta-analysis on “hidden” infections
Hence the need to see clearly, to investigate what was behind these “hidden” infections. “We conducted a meta-analysis following the preferred reporting elements for systematic reviews – explain the authors of the scientific research -. The goal was to estimate the aggregate rate of asymptomatic infections among the tested and confirmed populations. To do this we performed subgroup analyzes of the study location (Africa, Asia, Europe, North America and South America), examined the level of the countries examined (developed or developing), the population object of the analyzed studies ( air or cruise travelers, close contacts, community residents, health care workers or hospitalized patients, nursing home residents or staff, and pregnant women) “. And again: among other things, the publication period of the studies (June 2020 and earlier versus July 2020 and later), as well as the sample size per population tested and confirmed, were taken into consideration.
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Comparison of studies
The material was considerable. It started with 2,860 studies through database search and reference lists of articles and reviews. Of these, 282 underwent full-text reviews. In the final analysis, 95 were included, all focusing on information regarding the percentage of asymptomatic infections among the tested and confirmed populations.
Going into the details, of these last 95 papers, 44 (i.e. 46.32%) were transversal, 41 (43.16%) were cohort, 7 (7.37%) concerned case series and 3 (3.16 %) case series on transmission studies. As for the geographical area of origin, 74 studies (77.89%) were conducted in developed countries: 35 (36.84%) in Europe, 32 (33.68%) in North America and 25 (26.32%) ) in Asia.
Finally, by dividing the audience into categories, 37 jobs (38.95%) examined health workers or patients hospitalized; 17 (17.89%) residents or staff of nursing homes, 14 (14.74%) community guests; 13 (13.68%) pregnant women; 8 (8.42%) air travelers or cruise passengers and 6 (6.32%) close contacts.
The results
In the 95 studies included in the meta-analysis for the percentage of asymptomatic infections among the population tested, 29,776,306 individuals were tested, of which 11,516 had asymptomatic infection. And the results in some ways surprised. The aggregate rate of asymptomatic infections among the tested was 0.25%, declined as follows: 4.52% in guests or nursing home staff; 2.02% in air travelers or cruise passengers; 2.34% in pregnant women; 1.46% in close contacts; 0.75% in healthcare workers or hospital patients; 0.40% in community residents. The overall rate of asymptomatic infections was 0.90% in Europe, 0.47% in North America and 0.05% in Asia. And it was higher when the median age of the population tested was 60 years or older.
On the other hand, the result of asymptomatic infections in overt Covid patients was different: 19,884 people, including 11,069 asymptomatic. The percentage was 40.50% overall. In disaggregated terms: 54.11% for pregnant women; 52.91% for air travelers or cruise passengers; 47.53% for nursing home guests or staff; 39.74% for community residents; 30.01% for healthcare workers, hospital workers or patients; 26.94% for close contacts. Furthermore, the rate of asymptomatic infections was 46.32% in North America, 44.18% in Europe and 27.58% in Asia.
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“We need quarantines at the airport”
“The finding of a high number of asymptomatic infections among those who travel by plane or travel on a cruise, suggests that screening and quarantine upon arrival at the airport are important to reduce the infection – underline the researchers -. Furthermore, we discovered a conflicting finding: the percentage of asymptomatic infections among the tested population was relatively low among community residents, while it was consistent among confirmed Covid patients (39.74%). This leads us to think that, precisely because of those who have no symptoms but are positive for Coronavirus, the contagion can multiply. Therefore, within the communities, even the asymptomatic should be tested cyclically “. Just as, the experts add, “it should be done for workers in some specific sectors, such as air transport”. Then there are the health workers, who also count 30.01% of asymptomatic people able to carry the virus. “In this case too, surveillance is important for the control and transmission of infections – concludes the team of researchers -. But, at the same time, hand and personal hygiene must be maintained, as well as wearing protective devices for visitors to hospitals “.
The first Omicron report
Meanwhile, the Omicron variant is messing around the cards: it multiplies visibly, even if it seems less contagious, at least for the vaccinated. A study by the South African National Institute for Communicable Diseases, where the variant originated, reported on the MedRXiv prepress server, therefore awaiting review before its publication in an official scientific journal, says that the vast majority of infections with the Omicron variant do not require a hospitalization. More precisely, those who contract Covid-19 in the current fourth wave of infections are 80% less likely to be hospitalized if affected by Omicron than other variants. Furthermore, once in the hospital, the risk of serious illness does not differ from the other variants.
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5 times lower risk of hospitalization
The researchers compared current Omicron infections with those caused by the Delta variant in South Africa between April and November. And it was found that the risk of hospitalization in patients who contracted Omicron is one-fifth of that observed in patients with Delta. “To be clear, if Delta’s chance of being hospitalized was 5 percent, it would be 1 percent for Omicron,” said Guido Silvestri, a professor at Emory University in Atlanta, in a post on Facebook. But lethality also appears to be much lower than that of previous variants. The data from South Africa, out of almost 400 thousand cases, speaks of 0.26%, very low if compared with the 2.5% -4.0% of the first three waves. This is despite the fact that only 26.3% of the population is fully vaccinated (42% of adults). In line with this observation, the pressure on ICUs in South Africa, a country of 60 million inhabitants, remains low, with a total of 546 beds occupied (far from the Italian one, which exceeded a thousand serious patients).
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