Could that nasty cold you had just before the pandemic started two years ago have actually helped you avoid getting COVID-19 or maybe only having a mild case?
A new analysis by scientists at the University of Zurich in Switzerland on people exposed to circulating coronaviruses before the pandemic actually revealed a higher level of immunity against COVID-19. The study compared the immune response against SARS-CoV-2, the virus that causes COVID-19, and common coronaviruses before the pandemic.
“Every year when you catch a cold,” says Dr. Ulysses Wu, director of the infectious disease system and chief epidemiologist at Hartford HealthCare, “there is a 15% chance that one of them is an original coronavirus. – before COVID-19.
The four common types of coronaviruses, known as human coronaviruses (HCoV), which cause the common cold, also account for up to 6% of all hospitalizations for lower respiratory tract infections. An immune response against one of these viruses that also triggers immune protection against COVID-19 is known as cross-reactivity.
The researchers analyzed pre-pandemic serum samples from 825 people, measuring their immune response to each of the four HCoVs, and serum samples from 389 people who tested positive for COVID-19. They found that people infected with COVID-19 had lower levels of antibodies against HCoV than those who had not been infected with COVID-19. People with higher levels of HCoV antibodies, meanwhile, were less likely to require hospitalization from COVID-19.
For some people, the common cold also stimulates lymphocytes, a type of white blood cell that is an essential part of the immune system: T cells protect against infection and B cells create antibodies. (In the image above, B cells release antibodies that bind to the SARS-CoV-2 virus, neutralizing it.) T cells, which coordinate the immune response, remain on standby until the identification of a specific antigen. They then bind to the surface of the antigen.
T cells also respond to allergens and tumors. In infants, they develop immunity against common pathogens or antigens while building long-term memory. In adults, they maintain normal levels of protection and help reject common antigens. The effectiveness of T cells declines in older people, leaving the immune system more vulnerable to attack.
“We have to remember that vaccines work, not only in producing antibodies,” says Dr Wu, “but also in stimulating our B and T cells, which are our second and third lines of defence.”