Estimating R in Real time
Finding out how a particular measure affects R is not easy, since infections that occur today can take weeks to appear in disease reports. In 2004, the mathematician Jacco Wallinga of the Dutch National Institute for Public Health and the Environment and his colleagues published a statistical method for estimating R in real time, which is now used worldwide.
R, or the effective reproduction number, defines the rate of transmission for individuals in a society. In epidemic theory, R is measured by the number of transmissions of the virus from an individual.
The researchers also integrate data on people’s mobility patterns and behavior to make the estimates more accurate. It’s important to have real-time estimates of R, says Adam Kucharski, an LSHTM modeler: “If governments take a measure or lift it, they may have an idea of the immediate implications, rather than having to wait.” He says.
There is another unknown factor that will determine how safe it is to loosen the reins: immunity. Each infected and immunity-making person makes the spread of the virus more difficult. “If 30% or 40% of the population is immune, it really starts to change the whole picture, it helps a lot,” since it would reduce R by the same percentage, says Michael Osterholm, director of the Center for Disease Policy and Research Infectious Diseases at the University of Minnesota, Twin Cities.
Immunity will inevitably build up as more people become infected, but some researchers advocate faster immunity by allowing the virus to spread to young people, who are less susceptible to serious illness, while “Cocooning” patients at higher risk, like the elderly.
The UK launched the idea of ”collective immunity” in February, but withdrew, as did the Netherlands. “If collective immunity is achieved through widespread vaccination, it is devastating,” said Jeremy Konyndyk, senior project manager at the Center for Global Development. Even briefly, it left the UK “in a much worse place than necessary,” he said.
But some scientists say other countries should consider it once the pressure of the first wave of cases on their health systems has lessened. “Is it better to have a controlled burn in younger populations right now than to prevent it?” I think it is a very important conversation, “says Osterholm.
Skeptics doubt that vulnerable populations can really protect themselves. In many countries, several generations live under one roof and young people work in nursing homes. Scientists are also not sure that COVID-19 produces robust and long-lasting immunity. Several studies seek to answer these questions.
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