Wed. Sep 28th, 2022
Colorful Italian apartment building.
enlarge Even after the national lockdown ends, Italy continues to close residential buildings as clusters of cases develop there.

Italy was one of the countries first hit as the COVID-19 pandemic spread beyond its origins in China, as the country struggled with a sudden surge in cases that threatened to overwhelm its health services. But Italy turned out to be a success story, as an aggressive lockdown reversed the curve, causing new daily cases to drop from a peak of over 6,000 to a steady stream of around 300. Compared to a number of other industrialized democracies, this was a huge success.

Now a team of researchers largely based in Italy is looking more closely at the spread of the pandemic there and the impact of control measures. The researchers got most of a small town’s population to agree to testing before and after Italy’s lockdown, giving them insight into the behavior of the virus and how things have changed during the lockdown.

At the beginning

The location in question is called Vo’, a small town in northern Italy near Padua and Verona. Vo’ has just over 3,000 residents and most of them (86 percent) agreed to participate in the survey. At the end of February this year, just as Italy went into lockdown, all willing participants gave samples that were tested for the presence of SARS-CoV-2. Two weeks later, as Italy prepared to get out of lockdown, the participants were sampled again. Any health issues and contacts in the intervening time were examined, which also allowed people to trace contact networks.

This before-and-after sampling allowed the researchers to estimate how the virus had spread before the lockdown and how it spread during the lockdown, as well as monitor the development of symptoms in those infected. So the information the team collected should provide the kind of information we need to design more effective control measures and build better epidemiological models.

Italy reported its first known case of the coronavirus on February 20 this year, but the virus was clearly circulating before that. By the time the first survey was conducted on February 24, 73 people in Vo’ had already been infected, or 2.6 percent of the participants. In the following weeks, 40 percent of infected individuals never developed symptoms, which is consistent with a variety of studies indicating a high rate of asymptomatic infections. The researchers quantified the amount of virus present, but saw no difference between those with symptoms and those without.

Over the course of the study, 16 percent of those infected ended up in hospital. While most of these were over the age of 60, there were people under 60 who got severe cases.

Older individuals were also nearly three times more likely to develop an infection, also consistent with what has been seen elsewhere. This is in stark contrast to children. Of the 234 children in the study population, none became infected with the virus, even though some of them shared a home with an infected person.

In between and after

Just over half of the people the researchers found infected at the start of the study had no detectable virus two weeks later, indicating they had cleared the infection. The researchers estimated that it took an average of about nine days to clear the virus, with younger individuals and those with symptoms clearing it more quickly. For those who develop symptoms, the amount of virus present seemed to peak the day symptoms first became apparent.

The survey at the end of the lockdown shows how effective Italy’s policy approach has been. At that time, there were only 29 cases of active infections, or 1.2 percent of the total population. More importantly, only eight of those were new infections. The authors estimate that prior to the lockdown, each infected individual transmitted the virus to an average of 2.5 additional people. During the lockdown, that value dropped to 0.4, a rate at which the pandemic cannot be sustained.

Two of those eight newly infected individuals appear to have picked up the virus from an asymptomatic carrier, supporting the idea that contagiousness is not strictly related to symptoms. The authors also estimate that people can typically transmit the virus for about four to seven days over the entire course of their infection.

These figures should not be regarded as definitive. There are undoubtedly some details of the social interactions within Vo’ that do not apply elsewhere. But it’s also probably much closer to “normal” interactions than other instances where we’ve seen these kinds of detailed surveys of populations, such as cruise ships. And, with plenty of examples like Vo’, we can get a clearer picture of what the virus’ typical behavior looks like.

And, just as importantly, the data clearly shows that we can manage a potentially catastrophic pandemic through policy decisions without having to wait for a vaccine or fully effective treatment. As the authors put it, “Vo’s experience shows that despite the silent and widespread transmission of SARS-CoV-2, transmission can be controlled and represents a model for the systematic suppression of viral outbreaks under similar epidemiological and demographic conditions.” .” While the lockdown has clearly not eliminated infections in Italy, it has helped keep the frequency so low that less stringent restrictions combined with contact tracing now appear to be able to limit the spread of the pandemic in Italy.

Nature, 2020. DOI: 10.1038/s41586-020-2488-1 (About DOIs).

By akfire1

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