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Covid cases in the US have doubled in the past two weeks, and scientists are now racing to understand the delta variant that appears to be responsible for the vast majority of new infections. Disturbingly, delta is more contagious than other variants and also causes some cases of symptomatic “breakthrough” in vaccinated individuals.

While vaccines still overwhelmingly prevent severe illness and death, the delta variant is changing the way we think about coronavirus spread. Here are some answers to a few key questions about what it all means.

1. What makes the delta variant more contagious?

According to this Estimates from the CDC, the delta variant is almost twice as contagious as previous versions of the virus. Researchers are still trying to understand Mutations explain this, but preliminary studies show that changes to the spike protein make it more efficient both at catching receptors and at getting into your cells.

The delta variant also seems to lead to higher viral loads than other variants. Viral load is a measure of how much virus is in your nose and throat. a study They found that people with the delta variant had 1,000 times greater viral load at the start of infection than people infected with the original version of the virus. People with the delta variant also reached their peak viral loads faster, according to this yet peer-reviewed study.

2. How do scientists actually measure how contagious the delta variant is?

Viral load helps us understand how contagious a virus is. Coronavirus infections are spread through aerosols and droplets when an infected person coughs, sneezes or simply breathes – so the more virus particles a person has in their respiratory tract, 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 clean an infected person’s nose and remove any viral RNA from the swab. They then run the reaction, which looks for genetic material from viruses and replicates it repeatedly until there are enough copies for lab equipment to detect.

We usually focus on the endgame of PCR – whether a test finds material from a virus and whether it produces a positive result. But the researchers could also look at how long it took the machine to return this positive result – how many copies were needed to bring the viral material to a detectable level. The fewer copies or cycles needed to detect a virus, the more viral material was initially present.

This cycle number, called the cycle threshold or Ct, is the number that raises eyebrows at the Centers for Disease Control and Prevention. In Case clusters in Provincetown, Massachusetts, about 74% of concerned state residents have been vaccinated. Infected individuals tended to have similar Ct values, vaccinated or not. The CDC thought this might be an indication. vaccinated people can transmit the virus, perhaps as easily as unvaccinated people.

3. Can I still get covid even if I get vaccinated?

Yes, it is possible, although your infection is probably much less severe than that of an unvaccinated person.

The vast majority of infections are still found in unvaccinated people, he says. Liz Rogawski McQuadeAn infectious disease researcher at the University of Virginia, Dr. According to the news from Kaiser Family FoundationStates tracking the vaccination status of cases in the US find that 94% to 99.9% of cases are in unvaccinated people. And between 0.01% and 0.54% of everyone vaccinated, there was a breakthrough case.

A little studies They found that the efficacy of the vaccines was slightly lower against the delta variant, especially if you only received one dose of mRNA vaccine. But so far, it’s like vaccines still largely workSpecifically, in preventing many cases of serious illness, says Rogawski McQuade.

Vaccines may eventually need a little extra help against the delta variant – some companies pushing for booster shots. But experts say there is no evidence yet that boosters are necessary, and WHO protects That initial vaccines for the rest of the world should take precedence over booster vaccines for people in rich countries.

4. What about transmission? Can vaccinated people spread the delta variant?

It seems so, but the research is still in the early stages.

While Ct values ​​can be used as a proxy for viral load, there are a few issues with trying to assume too much based on this number, especially when it comes to vaccinated people. Monica GandhiAn infectious disease researcher at the University of California at San Francisco, Dr.

First of all, PCR takes all kinds of genetic material, even from dead viruses. If your immunized immune system is starting to fight the infection, “you may have a lot of viral particles in your nose, but they may not work,” Gandhi says. To really know how contagious someone is, you have to take those viruses and see if they are alive and infect people. Gandhi noted that the CDC’s data is still outstanding.