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Again: unpublished data, no details, no peer review, science press release. It’s not good. But big, as political writers sometimes say, if that’s true. People infected with the virus but without symptoms – asymptomatic spreaders – appear to be one of the reasons the disease is pandemic. No one knows what the reason is.
Many other respiratory viruses overlap with symptoms and transmission – sometimes the symptoms themselves, such as coughing, are how the virus passes from one infected person to another. The time between infection and symptoms, called the incubation period, does not last long. “We know that with influenza the incubation period is relatively short and people can shed the virus for about a day,” says Arnold Monto, an epidemiologist at the University of Michigan who chairs the Vaccines and Medicines Advisory Committee. related biologics from the FDA, which helps make decisions about the approval of new vaccines. “We can infect a ferret with the flu and they get sick, but if they don’t cough or do what ferrets do when they are symptomatic, they don’t also transmit.
The assumption that this was also true for Covid-19 provided the seam for many cosplay pandemic protection, like temperature checks and symptom surveys. “A lot of the things we did in the beginning were based on the fact that with traditional SARS there wasn’t a lot of transmission from asymptomatic individuals,” says Monto. “Symptomatic people tend to transmit respiratory infections more than asymptomatic people. We think that’s probably true with Covid, but it’s becoming increasingly clear that asymptomatic people are also involved in transmission.
The problem is that a Covid-19 vaccine that only prevents the disease – that is, the symptoms – could do not prevent infection with the virus or its transmission to others. In the worst case, a vaccinated person could still be an asymptomatic carrier. It could be bad. More younger people tend to catch the virus, but more older people tend to die from it; socioeconomic status and ethnicity also have an impact on death rates. Some people have relatively mild symptoms; other people have symptoms that persist for months. And perhaps more importantly, a vaccine is the only way to achieve herd immunity without bloodshed. As politicized as the concept has become, herd immunity is essentially the sum of direct protection – what you might get if you are vaccinated – and indirect protection, the safety provided by the fact that people around you are not. do not pass the disease on to you because either they already had the disease themselves or because they had been vaccinated against it. While those vaccinated can still be asymptomatic spreaders, this means less indirect protection for the herd.
This is really important because there are not enough vaccines for everyone. Not yet anyway. Some groups of people will go first. The characteristics of the available vaccines would determine, in a perfect world, who these people should be. Older people, in whom severe illness is more likely to lead to death, may be the first to avoid the illness. The one that prevents infection and transmission could be left to essential workers and frontline caregivers. “Part of our concern is that we want to get it right early in the allocation phase, making sure we target the vaccine as best as you can,” says Grace Lee, professor of pediatrics at the Stanford School of Medicine. and member of the CDC Advisory Committee on Immunization Practices. “If the only thing it was doing was protecting itself from serious disease, you would want to look at the people with serious disease and only use it there, and nowhere else.”
This will certainly not be the situation. The vaccines will likely all have an effect on transmission. But right now, no one knows how much, or which one is better, or for whom – because so far only AstraZeneca has even a hint of data investigating the problem.
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