More than half of COVID-19 transmission is due to people with no symptoms, so says a model developed by a professor at University of Florida’s (UF) Emerging Pathogens Institute.
A third or more of these cases will need to be isolated, in addition to most symptomatic cases, to quell the pandemic.
This is emerging as Nigeria’s COVID-19 infection rate hits 34,257 with the 643 new cases recorded on Wednesday.
Nigeria Centre for Disease Control (NCDC) that made this known, also reports six deaths last 24 hours that has now taken the country’s death toll to 760.
According to NCDC, ‘’till date, 34,259 cases have been confirmed, 13,999 cases have been discharged and 760 deaths have been recorded in 36 states and the Federal Capital Territory, Abuja.’’
Of the 643 new cases from 19 states of the federation, Lagos held on as the epicentre of the virus with 230 cases, followed by Oyo’s – 69, Abuja – 51, Edo – 43, Osun – 35, Rivers – 30, Ebonyi – 30, Kaduna – 28, Ogun 27, Ondo – 23, Plateau – 20, Benue – 17, Enugu – 16, Imo – 10, Delta – six, Kano – four, Nasarawa – two, Kebbi and Ekiti one case each.
However, the Emerging Pathogens Institute was created in 2006 to provide a world-class research environment to facilitate interdisciplinary studies of emergence and control of human, animal and plant pathogens of concern to Florida, to the nation and to the world.
More than half of COVID-19 transmission is driven by people who show no symptoms, according to new research published by the Proceedings of the National Academy of Sciences.
The findings could directly influence the design of test-and-trace containment policies that aim to lower the rising numbers of infections in the United States.
Researchers have scrambled to understand the dynamics of how COVID-19 spreads, as the disease has rapidly metastasized around the globe.
Determining when people are infectious and able to spread the virus to others, is key to knowing when they should be isolated to prevent their passing to others the virus which causes COVID-19.
Burton Singer, a professor in UF’s College of Liberal Arts and Sciences Department of Mathematics, and the Emerging Pathogens Institute, contributed to the research and data analysis.
Singer has often partnered with the study’s senior author, Alison Galvani of Yale University’s School of Public Health.
“Our paper gets to the heart of the asymptomatic and pre-symptomatic cases”, Singer says. “But it’s also telling us that if we want to stop this pandemic, we need to focus on finding the asymptomatic cases.”
The researchers refined a model they’d previously developed to examine estimates of hospital occupancy rates during the pandemic.
The new work incorporates a data set that characterizes the infectiousness of asymptomatic and pre-symptomatic people infected with COVID-19.
Asymptomatic people carry the virus, though they never become ill. Pre-symptomatic people, on the other hand, will eventually develop symptoms but are able to spread the virus to others before their symptoms develop—before they may even know they are ill.
The team’s new work estimates that 51.4% to 53.6% of transmission comes from those not showing symptoms; 48%-47% of this comes from people in the presymptomatic stage, while 3.4%-6.6% comes from those who will never develop symptoms.
The range of these findings is based on two separate studies by others, one which found that 18% of all COVID-19 infections were without symptoms, while the other pegged this number at 31%.
The new model estimates that even if all cases of people with symptoms are immediately isolated, the disease will continue to spread stealthily via symptomless infections.
This means that many people are silently transmitting the virus and driving the pandemic’s spread—either because they do not yet know they are ill, or because they are asymptomatic carriers who are infectious but never develop symptoms.
“The single biggest lesson of this is that we need to prioritize contact tracing,” Singer says. “Without that, we won’t get any traction against the virus. But the question is, where will it be most effective?”
In densely populated areas where the virus has already taken hold, it will be harder to start serious contact tracing efforts and have them be effective, Singer says, due to the sheer volume of people exposed and ongoing transmission.
But in less densely populated areas that currently have a low amount of COVID-19 infections per capita, putting effective contact tracing efforts in place early will have deep and long-term payoffs in protecting the population against the pandemic.
However, having a rigorous test-and-trace policy in place is only one side of the coin. The other is having cooperative citizens who will not only answer their phones for public health workers but also comply with quarantine rules.
The powerful effect of test, trace and isolate strategies in fighting the COVID-19 pandemic are showcased by nations such as Iceland and New Zealand, Singer says. These countries have pushed transmission to low or nonexistent levels.
To drive the virus’ attack rate below 1% and quell the epidemic, the model estimates that between 33% and 42% of asymptomatic cases would need to be detected and isolated—in addition to detecting and isolating the majority of the symptom-based cases.
For this to happen, a robust test-and-trace campaign is needed for society to safely resume its normal, pre-pandemic level of economic and social activity.
While the paper drives home the value of testing, tracing and isolating sick or exposed individuals, it also enforces the existing strategies of wearing a mask when around others—even if the wearer does not feel ill—social distancing when in public places and limiting activities outside the home as much as possible.
“All is not lost in the US”, Singer says. “We can still turn this around with the right leadership. Especially in areas where there may be a spark of COVID-19 spread starting, but it has not yet taken off.”
In the mean time, doctors in France have described what they said was the first confirmed case of a newborn infected in the womb with COVID-19 by the mother.
The baby boy, born in March, suffered brain swelling and neurological symptoms linked to COVID-19 in adults, but has since recovered, they reported Tuesday in the journal Nature Communications.
Earlier research had pointed to the likely transmission of the virus from mother to foetus, but the study offers the first solid evidence, said senior author Daniele De Luca, a doctor at Antoine Beclere Hospital near Paris.
“We have shown that the transmission from the mother to the foetus across the placenta is possible during the last weeks of pregnancy,” he said.
Last week, researchers in Italy said that data on 31 pregnant women hospitalised with COVID-19 “strongly suggested” that the virus could be passed on to unborn infants.
A JAMA study in March reporting on a similar number of pregnant COVID-19 patients came to a similar conclusion.
But evidence remained circumstantial.
“You need to analyse maternal blood, amniotic fluid, the newborn’s blood, the placenta, et cetera,” De Luca said by phone.
“Getting all of these samples during a pandemic with emergencies everywhere has not been easy. This is why it has been suspected but never demonstrated.”
De Luca and his team pulled together this data for the case of a pregnant woman in her twenties admitted to his hospital in early March.
Because the baby was delivered by caesarean section, all of the potential sources and reservoirs of the virus remained intact.
The concentration of SARS-CoV-2, the technical name given to the virus, was highest in the placenta, the researchers found.
“From there it passed through the umbilical cord to the baby, where it develops,” De Luca said. “That is the pathway of transmission.”
The baby began to develop severe symptoms 24 hours after birth, including severe rigidity of the body, damage to white matter in the brain, and extreme irritability.
But before doctors could settle on a course of treatment, the symptoms began to recede. Within three weeks, the newborn had almost fully recovered on his own.
Three months later, his mother is without symptoms.
“The bad news is that this actually happened, and can happen,” De Luca said. “The good news is that it is rare—very rare compared to the global population.”
Among the thousands of babies born to mothers with COVID-19, no more than one or two percent have tested positive for the virus, and even fewer show serious symptoms, said Marian Knight, a professor of maternal and child population health at the University of Oxford who was not involved in the research.
“The most important message for pregnant women remains to avoid infection through paying attention to hand washing and social distancing measures,” she said.
Others said the case study sheds light on how the virus passes from mother to child.
“This report adds knowledge to a possible mechanism of transfer to the baby, via the placenta,” commented Andrew Shennan, a professor of obstetrics at King’s College London.
“But women can remain reassured that pregnancy is not a significant risk factor for them or their babies with COVID-19.”