Covid cases in the United States have doubled in the past two weeks, and scientists are now rushing to understand the delta variant, which appears to account for the vast majority of new infections. Disturbingly, the delta is more contagious than other variants and has also caused symptomatic cases of “breakthrough” in those vaccinated.
While vaccines still massively prevent serious illness and death, the delta variant has changed the way we think about the spread of the 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 figure out mutations that explain this, but preliminary studies suggest that changes in its spike protein make it more efficient at both grabbing receptors and entering your cells.
The delta variant also appears to lead to higher viral loads than the other variants. Viral load is a measure of the amount of virus in your nose and throat. A study found that at the start of their infection, people with the delta variant had viral loads 1,000 times higher than those infected with the original version of the virus. People with the delta variant also reached their peak viral load faster, according to this study, which has yet to be peer reviewed.
2. How do scientists actually measure the degree of contagiousness of the delta variant?
Viral load helps us understand how contagious a virus is. Coronavirus infections are spread by aerosols and droplets when an infected person coughs, sneezes, or simply breathes. So the more virus particles there are in a person’s airways, the more likely that person is to infect someone else.
To measure viral load, researchers use a lab method called a polymerase chain reaction, or PCR. They swab the nose of an infected person and extract any viral RNA that is on the swab. Then they run the reaction, which searches for the genetic material of viruses and copies it over and over again, until there are enough copies for lab equipment to detect.
We usually focus on the final phase of PCR, which is whether a test finds material from a virus, which produces a positive result. But researchers can also watch how long the machine took to return this positive result – how many copies were needed to bring the viral material to detectable levels. The fewer copies, or cycles, it took to detect a virus, the more viral material there was to start with.
This number of cycles, called cycle threshold, or Ct, is the number that raised eyebrows at the Centers for Disease Control and Prevention. In one cluster of cases in Provincetown, Massachusetts, approximately 74% of the state residents involved have been vaccinated. Infected people tended to have similar Ct values whether or not they had been vaccinated. The CDC thought this could be an indicator that vaccinated people could transmit the virus, perhaps as easily as unvaccinated people.
3. Can I still get sick with covid, even if I am vaccinated?
Yes, it is possible, although your infection will likely be much less severe than that of an unvaccinated person.
The vast majority of infections are still in unvaccinated people, according to Liz Rogawski McQuade, infectious disease researcher at the University of Virginia. According to reports from the Kaiser Family FoundationUS states that track the immunization status of cases find that between 94% and 99.9% of cases involve unvaccinated people. And of all those who were vaccinated, between 0.01% and 0.54% experienced a revolutionary case.
Some studies have found that vaccine efficacy is somewhat lower against the delta variant, especially if you have only received one dose of an mRNA vaccine. But so far it seems that vaccines still work widely, especially in the prevention of many cases of serious illness, explains Rogawski McQuade.
Vaccines could possibly need a little extra help against the delta variant – some companies are push for booster shots. But experts say there is no evidence yet that boosters are needed, and the WHO maintains that initial vaccines for the rest of the world should take precedence over booster shots for people in rich countries.
4. What about the transmission? Can vaccinated people spread the delta variant?
It seems so, but research is still in its early stages.
While Ct values can be used as a proxy for viral load, there are a few issues with trying to overstate based on this number, especially when it comes to people who have been vaccinated, according to Monique Gandhi, infectious disease researcher at the University of California at San Francisco.
First of all, PCR collects all kinds of genetic material, even dead viruses. If your vaccinated immune system has started to fight off the infection, “you may have a lot of virus particles in your nose, but they may not work,” Gandhi says. In order to really know how contagious a person is, you need to take these viruses and see if they are alive and capable of infecting people. The CDC noted that this data is still pending, Gandhi said.