MANILA, Philippines – An oncologist explains the possible reasons why some people with COVID-19 have little or no symptoms, citing recent studies and emerging data to prove his theories.
According to Dr. Vincent Rajkumar, an oncologist in India, there are at least 4 possible reasons behind asymptomatic patients:
1) A rapid immune response that conquers the virus
In a paper published in the scientific journal, Cell, a group of researchers from Karolinska Institute in Solna, Sweden, wrote that a rapid immune response might be responsible for conquering the virus even before it could spread in the body.
They discovered that asymptomatic and mildly symptomatic patients have high SARS CoV-2 specific cytotoxic T cell responses. This means that as soon as the virus gets inside the body, the person’s immune system rapidly produced a lot of these special T cells to fight off the infection – and they won.
2) Pre-existing cross reactive immunity
Citing numerous studies, Rajkumar said that it is possible for people to have cross reactive T cells presumably from prior infections with other forms of coronavirus. Though this won’t prevent a person from getting COVID-19, the presence of these T cells could help attenuate the severity of the disease.
He believes that this is the reason why India has less mortality compared with other places.
3) Genetic factors
While lots of studies still need to be done to correlate genetic factors with resistance to COVID-19, Rajkumar said there are already several that show how genetics appears to be a big help.
“Genetic factors: Lots to learn. But from ABO group to ACE polymorphisms studies are coming out on genetic susceptibility. An interesting factor associated with severe disease is TLR-7 mutations on X chromosome: also explains milder disease in women,” Rajkumar wrote.
4) Low viral load at time of infection
Rajkumar argues that the possibility of a low viral load at the time of infection could lead to the body creating enough antibodies to fight the infection.
Because only a small load of the virus enters, this gives the body a fair warning without the virus being able to quickly cause a severe infection in that person.
“NEW PERSPECTIVE PIECE: masks can be leaky but even when they don't catch all the virus, it appears that they catch enough of it to only cause mild disease. Can less viral load result in less severe disease? That's been seen for other pathogens. How about for SARS-CoV-2?” muses Dr. Ali Nouri, whose tweet was retweeted by Rajkumar to argue this point.
While these are all just hypotheses, Rajkumar believes that he is on the right track. But that does not mean it will be easy to keep people safe from the virus now that we know why some patients only exhibit very little or no symptoms at all.
“I study cancers of the immune system. My job is to kill the cells that help us fight infection. The same cells that make antibodies. To kill them, we have to understand them. And the one think I’ve learnt is that it’s extraordinarily hard to get rid of them: Normal or cancerous,” Rajkumar said.
“Which is why I have hope that natural infection or vaccines will be effective. Maybe not in preventing a recurrent infection. But certainly attenuating the disease and making future versions more like regular flu or hopefully milder.”
— Joy Adalia, The Summit Express
According to Dr. Vincent Rajkumar, an oncologist in India, there are at least 4 possible reasons behind asymptomatic patients:
1) A rapid immune response that conquers the virus
In a paper published in the scientific journal, Cell, a group of researchers from Karolinska Institute in Solna, Sweden, wrote that a rapid immune response might be responsible for conquering the virus even before it could spread in the body.
They discovered that asymptomatic and mildly symptomatic patients have high SARS CoV-2 specific cytotoxic T cell responses. This means that as soon as the virus gets inside the body, the person’s immune system rapidly produced a lot of these special T cells to fight off the infection – and they won.
2) Pre-existing cross reactive immunity
Citing numerous studies, Rajkumar said that it is possible for people to have cross reactive T cells presumably from prior infections with other forms of coronavirus. Though this won’t prevent a person from getting COVID-19, the presence of these T cells could help attenuate the severity of the disease.
He believes that this is the reason why India has less mortality compared with other places.
3) Genetic factors
While lots of studies still need to be done to correlate genetic factors with resistance to COVID-19, Rajkumar said there are already several that show how genetics appears to be a big help.
“Genetic factors: Lots to learn. But from ABO group to ACE polymorphisms studies are coming out on genetic susceptibility. An interesting factor associated with severe disease is TLR-7 mutations on X chromosome: also explains milder disease in women,” Rajkumar wrote.
4) Low viral load at time of infection
Rajkumar argues that the possibility of a low viral load at the time of infection could lead to the body creating enough antibodies to fight the infection.
Because only a small load of the virus enters, this gives the body a fair warning without the virus being able to quickly cause a severe infection in that person.
“NEW PERSPECTIVE PIECE: masks can be leaky but even when they don't catch all the virus, it appears that they catch enough of it to only cause mild disease. Can less viral load result in less severe disease? That's been seen for other pathogens. How about for SARS-CoV-2?” muses Dr. Ali Nouri, whose tweet was retweeted by Rajkumar to argue this point.
While these are all just hypotheses, Rajkumar believes that he is on the right track. But that does not mean it will be easy to keep people safe from the virus now that we know why some patients only exhibit very little or no symptoms at all.
“I study cancers of the immune system. My job is to kill the cells that help us fight infection. The same cells that make antibodies. To kill them, we have to understand them. And the one think I’ve learnt is that it’s extraordinarily hard to get rid of them: Normal or cancerous,” Rajkumar said.
“Which is why I have hope that natural infection or vaccines will be effective. Maybe not in preventing a recurrent infection. But certainly attenuating the disease and making future versions more like regular flu or hopefully milder.”
— Joy Adalia, The Summit Express
