It‘s been a big puzzle of the pandemic: Why are children so much less likely than adults to be infected with the novel coronavirus and, if infected, less likely to get sick?
One possible reason could be that many children already have antibodies to other coronaviruses, according to researchers at the Francis Crick Institute in London. About one in five common colds in children is caused by viruses in this family. Antibodies to these viruses can also block SARS-CoV-2, the novel coronavirus that is causing the pandemic.
In a study published in Science on Friday, the group, led by George Kassiotis, who heads the institute’s retroviral immunology lab, reports that on average just 5% of adults had these antibodies, compared to 43% of children.
Researchers who were not involved in the study were intrigued by the discovery. H. Benjamin Larman, an immunologist at the Johns Hopkins School of Medicine, called the study “a well-conducted study that offers a compelling theory supported by their data.”
Stephen J. Elledge, professor of genetics at Harvard Medical School and Brigham and Women’s Hospital, had a similar response. He and others found that many people had antibodies to the common cold caused by other coronaviruses; in laboratory studies, these antibodies also block the novel coronavirus.
In March, as the pandemic was just beginning, Dr Kassiotis and his colleagues decided to develop a very sensitive antibody test. To assess it, they looked at blood samples taken before the pandemic from more than 300 adults and 48 children and adolescents, comparing them with samples from more than 170 people who had been infected with the new coronavirus.
Scientists expected that samples taken before the pandemic would not contain antibodies attacking the new coronavirus. These must have been the controls for the test that scientists were developing.
Instead, they found that many children, and some adults, carried a particular antibody that can prevent coronaviruses, including the new one, from entering cells. This antibody attaches to a peak that comes out of coronaviruses.
Although the tip of the peak is unique to the new coronavirus, the basis is found in all coronaviruses, Dr Kassiotis said. In lab tests, antibodies to the base of the peak prevented the new coronavirus from entering cells in order to reproduce.
Now, the researchers plan to expand their study to monitor thousands of children and adults. Some have antibodies that can block the new coronavirus in lab tests. Others don’t.
“If they have the pandemic strain, are they protected?” Asked Dr. Kassiotis. Will they get sick, he wondered, or will the infection be virtually undetectable?
Dr. Elledge and his colleagues at Harvard have developed their own highly specific, sensitive and comprehensive antibody test, VirScan. It is able to detect a diverse collection of antibodies directed at any of the more than 800 locations of the novel coronavirus, including the antibody studied by Dr Kassiotis and his colleagues.
After examining blood drawn from 190 people before the pandemic emerged, Dr Elledge and colleagues concluded that many already had antibodies, including one targeting the base of the peak – presumably from related coronavirus infections that cause colds.
But while adults can catch one or two colds a year, Dr. Elledge said, children can get as many as a dozen. As a result, many develop floods of anti-coronavirus antibodies which are present almost continuously; they can alleviate cold symptoms or even leave children with asymptomatic but still contagious colds.
While adults may not have detectable antibodies to the coronavirus, many may be able to make antibodies quickly if they are infected with coronavirus.
In typical viral infections, the immune system sheds antibodies to fight the virus. When the infection is suppressed, the antibodies, no longer needed, decrease in number. But the body ends up with what are called memory cells which allow antibody production to increase rapidly if the virus tries to invade again.
So why do we have a pandemic? Shouldn’t most of us be protected by memory cells left over from other coronavirus infections?
Confused by the terms relating to coronavirus testing? Let us help you:
- Antibody: A protein produced by the immune system that can recognize and attach precisely to specific types of viruses, bacteria or other invaders.
- Antibody test / serological test: A test that detects specific antibodies to the coronavirus. Antibodies start to appear in the blood about a week after the coronavirus has infected the body. Because antibodies take so long to develop, an antibody test cannot reliably diagnose an ongoing infection. But it can identify people who have been exposed to the coronavirus in the past.
- Antigen test: This test detects pieces of coronavirus protein called antigens. Antigen tests are quick, take only five minutes, but are less accurate than tests that detect the genetic material of the virus.
- Coronavirus: Any virus belonging to the Orthocoronavirinae virus family. The coronavirus that causes Covid-19 is known as SARS-CoV-2.
- Covid19: The disease caused by the new coronavirus. The name is the abbreviation for coronavirus disease 2019.
- Isolation and quarantine: Isolation is the separation of those who know they have a contagious disease from those who do not. Quarantine refers to restricting the movement of people who have been exposed to a virus.
- Nasopharyngeal swab: A long flexible stick with a soft swab that is inserted deep into the nose to take samples from the space where the nasal cavity meets the throat. Samples for coronavirus tests can also be collected with swabs that do not penetrate as deep into the nose – sometimes called nasal swabs – or oral or throat swabs.
- Polymerase chain reaction (PCR): Scientists use PCR to make millions of copies of genetic material in a sample. Tests using PCR allow researchers to detect the coronavirus even when it is rare.
- Viral load: The amount of virus in a person’s body. In people infected with the coronavirus, the viral load may peak before starting to show symptoms, if symptoms do appear.
“It’s quite possible that you lose your memory over time,” Dr. Elledge said. He suspects that the new coronavirus could interfere with the activation of memory cells capable of responding to infection.
An infection “might give you a fuzzy memory that fades over time,” he said. If this is the case, a very recent infection with a common cold coronavirus would be necessary to protect against the new coronavirus, and even then the protection might only last for a limited time.
The new coronavirus is said to have hampered the production of antibodies that specifically attack it. This could explain why children, with their seemingly continuous colds, are much better off than adults.
Dr Elledge said that if he was right about the loss of memory cells, it bodes well for vaccines. A vaccine stimulates the production of antibodies without the presence of a virus. So the virus “is not in the background, disrupting the formation of memory cells,” he said.
Another possibility is that most adults are actually protected by memory cells from previous cold infections. Although few of them have enough antibodies in their blood to protect them at any given time, they may be able to quickly make antibodies to lessen the impact of the new coronavirus.
This could explain why many infected adults recover quickly.
“We’re focusing on those who get really sick, but 95 to 98 percent of those who get the virus don’t have to go to the hospital,” Dr. Elledge said. “There are a lot of people getting better.”
This happened to Dr. Larman and his family of five. Four of them fell ill with Covid-19, the disease caused by the new coronavirus, in July. None were seriously ill, and their 4 year old son was completely spared.
“My son was not isolated from us and therefore highly exposed,” said Dr Larman. “He tested negative twice, so we certainly suspect he had some form of pre-existing immunity.”