ITHACA, N.Y. (WENY) — If you've been following updates about Coronavirus, you may have heard the term viral load. Health experts say viral load is what gives a disease, like COVID-19, the ability to spread from one person to another.

Viral load is the amount of virus a person gets through infection and exposes others to. It can be measured in two ways. Luis Shang, professor of virology at Cornell University, says one is more accurate but harder to do. 

"Which is to measure the infectivity, the total infectivity a person gets," Schang said.

The other method is to measure the viral genome or set of genes in a virus.

"Each infectious particle has a genome. We also produce, this is common for any virus, a large number of non-infectious particles that still have genomes," Schang said.

Accurately measuring a large amount of viral load, or infectious RNA in the genome is almost impossible. 

"When we measure viral RNA, we can measure only the genomes and there are ways of doing that or we can measure all of the RNA in a cell, including the genome lengths and the shorter fragments."

The mRNA that's found in the vaccine isn't the same as the RNA that is found in a sick person's cells.

"What is in the vaccine is a gene from the virus, so-called spike or S clone and separated from anything else from the virus," Schang said.

According to Schang, vaccinated people don't have any viral load. Only people who are sick with COVID-19 spread the disease from one person to another when they start to shed the virus. 

"If there are five people in an office and four are infected, they will shed more virus. The vrial load in the location will be higher than if there is only one person that is infected in the same room."

Schang says viral shedding is what allows a virus to travel from one person to the next.

"There are two factors in the influenza viral shedding. One is the viral load on the upper respiratory tract. The more virus we have in the upper respiratory tract, the more that we shed it."

Infected people could be in a room and leave. If someone who is immuno-compromised walks into that same, but now empty room, Schang says they could shed enough virus into the air and get them sick.

"What we'll call the dose to result in very serious disease in an immuno-compromised person are much lower than the dose that would result in most healthy people," Schang said.

As long as the number of COVID-19 cases is high, people with a weakened immune system will remain vulnerable. According to Schang, even with the vaccine and booster shots, immuno-compromised people can't mount an effective immune response. 

"In the case of a virus like this one that replicates so fast, they are at a serious disadvantage. The virus tends to beat the immune response."

If people don't take the steps to stop the virus from spreading, like vaccination and mask-wearing, Schang says vulnerable people will continue to get sick and die.