COVID cases in the United States have doubled in the last two weeks, and scientists are now racing to understand the delta variant, which appears to represent the vast majority of new infections. Disturbingly, the delta is more contagious than other variants, and has also caused some symptomatic “breakthrough” cases in vaccinated individuals.
Although vaccines still greatly prevent serious illness and death, the delta variant has changed our view of the spread of coronavirus. Here are some answers to some important questions about what it all means.
1. What makes the delta variant more contagious?
According to CDC estimates, the delta variant is almost twice as contagious as previous versions of the virus. Researchers are still trying to understand mutations that explain this, but preliminary studies suggest that changes in its spike protein make it more efficient to capture receptors and enter your cells.
The delta variant also appears to lead to a higher virus load than the other variants. Virus load is a measure of the amount of virus in the nose and throat. One study they found that at the beginning of the infection, people with the delta variant had a viral load 1000 times higher than those infected with the original version of the virus. People with the delta variant also reached a peak viral load more quickly, according to this study, which has not yet passed expert review.
2. How do scientists actually measure how contagious the delta variant is?
The virus load helps us understand how contagious the virus is. Coronavirus infections are spread by aerosols and droplets when an infected person coughs, sneezes or just breathes – so the more virus particles in someone’s airways, the more likely that person is to infect someone else.
To measure viral load, researchers use a laboratory method called polymerase chain reaction or PCR. They wipe the nose of an infected person and extract any viral RNA found on the swab. They then trigger a reaction, which searches for genetic material from the virus and copies it over and over again, until there are enough copies that laboratory equipment can detect.
We usually focus on the end of the PCR – whether the test finds material from the virus, which gives a positive result. But researchers can also look at how much the machine needed to return a positive result – how many copies it took to bring the viral material to a detectable level. The fewer copies or cycles it took to detect the virus, the more viral material there was to begin with.
This number of cycles – called the cycle threshold or Ct – is the number that raised eyebrows at the Centers for Disease Control and Prevention. U a group of cases in Provincetown, Massachusetts, about 74% of the state’s population was vaccinated. People who got the infection had similar Ct values, whether they were vaccinated or not. The CDC felt this could be an indicator vaccinated people can transmit the virus, perhaps as ready as unvaccinated people.
3. Can I still get sick from covid, even if I have been vaccinated?
Yes, it is possible, although your infection will probably be much easier than that of an unvaccinated person.
The vast majority of infections are still in unvaccinated people, he says Liz Rogawski McQuade, a researcher on infectious diseases at the University of Virginia. According to reports from Kaiser Family Foundation, U.S. states that monitor vaccination status find that between 94% and 99.9% of cases are in unvaccinated people. And of all those vaccinated, between 0.01% and 0.54% experienced a revolutionary case.
Some studies they found that the effectiveness of the vaccine was slightly lower than the delta variant, especially if you received only one dose of the mRNA vaccine. But for now, it looks like it is vaccines still work to a great extent, especially in preventing many cases of serious illness, says Rogawski McQuade.
Vaccines may eventually need additional help against the delta variant – some companies have looking for amplified recordings. But experts say there is no evidence yet that boosters are necessary, and WHO maintains that initial vaccines for the rest of the world should take precedence over auxiliary injections for people in rich countries.
4. What about transmission? Can vaccinated people spread the delta variant?
It seems so, but research is still at an early stage.
Although Ct values can be used as a substitute for viral load, there are several problems in trying to assume too much based on that number, especially when it comes to vaccinated individuals, according to Monica Gandhi, an infectious disease researcher at the University of California, San Francisco.
First of all, PCR collects all types of genetic material, even from dead viruses. If your vaccinated immune system has started to fight the infection, “you may have a lot of viral particles in your nose, but they may not work,” says Gandhi. To really know how contagious someone is, you need to take those viruses and check if they are alive and if they can infect people. The CDC has noted that this data is still outstanding, Gandhi says.