Читать книгу Viruses: More Friends Than Foes (Revised Edition) - Karin Moelling - Страница 21

We routinely learn of the number of people who have recovered from SARS-COVID-19.

They must have produced antibodies against the virus. There are antibody tests available: strips with viral antigens react with a person’s antibodies present in a drop of blood, and again the result is revealed by some color system. Antibodies, immunoglobulins such as IgG, arise about two weeks after recovery. Normally such antibodies are thought to protect the carrier from a reinfection, if they are strong enough. The view has been propounded that people do not have any antibodies against this novel virus, as our immune systems have never encountered it. This may not quite be so, since the four seasonal coronaviruses, appearing regularly in winter, may cross-react. Recently some data have indicated that 15% to 20% of the population in certain regions such as New York City have antibodies, some of them without having been sick — which leads to the question of whether they were infected with the new virus without knowing it or whether previous infections may have contributed to this result. This will be tested on a large scale. The total number of infected people plays a part in determining the number of protected people.

Could antibodies be too weak to afford protection? Or too short-lived? Could they even do harm? There are indeed opposite reactions known for some viruses, which can enhance the disease upon reinfection. This is designated as antibody-dependent enhancement (ADE) and is known for Dengue viruses. It is rare and may hopefully not apply to CoV-2, but is very relevant for forthcoming immunizations. Do vaccines protect against infections, and are they safe?

Before vaccines become available, antibody tests would be very useful — quick tests with immediate answers. Then people could travel, teach children and go to work without any risk. However, these tests are simple and sometimes not quite exact enough and need to be correctly done. The rate of false results can be limiting for commercial approval. Some such tests have already entered the market.