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The headlines give cause for optimism: Moderna and Biontech / Pfizer’s corona vaccine candidates are said to offer 90 percent or more protection against the disease, and a vaccine from British-Swedish pharmaceutical company AstraZeneca reports at least 70 percent effective. All hopes now turn to the fact that vaccines will help stop the spread of the pathogen for the foreseeable future and contain the pandemic. But how long does the body have at least some protection against viruses?
There may not yet be long-term studies available that provide the corresponding answers; the duration of the study so far has been a few months. A recent study from the La Jolla Institute of Immunology in California examined infected people. Consistent with this, both antibodies and T cells, two of the core weapons of our immune system, are still detectable for at least five months after symptoms appear, even if symptoms are mild. The study was published as a pre-print, so it has not yet been reviewed by independent experts.
Mild course of the disease
For Thomas Jacobs of the Bernhard Nocht Institute for Tropical Medicine in Hamburg, these observations are encouraging in view of the multi-arm reaction of our immune system. Make two points: In this study there is what is known as sterile immunity, which depends on a high number of neutralizing antibodies. If the body has many of them, a virus is detected before it can enter cells. The corresponding vaccines would probably produce an antibody response even better than a natural infection. As long as there are enough antibodies, robust, if not sterile, immunity can be assumed, Jacobs said.
Furthermore, the T cell response was also detectable for several months. This means that symptoms of Covid 19 disease can be expected to decrease, says Jacobs. Such clinical immunity would ensure that sick people only have cold symptoms, for example, as occurs with more harmless coronaviruses.
More efficient immune response after vaccination
At present, a sterile lifelong protective effect from vaccines cannot be assumed. However, the results of the prepress study would provide a positive framework for the expected immunity of the vaccine.
Another study group recently reported that T cells are still detectable six months after a Sars CoV-2 infection. “This is very promising news: if a natural infection with the virus can produce a robust T-cell response, it may mean that a vaccine could do the same,” said Fiona Watt, CEO of the UK Medical Research Council. , in an article. from the specialized magazine “The BMJ”.
Carsten Watzl, an immunologist at the Leibniz Institute for Labor Research at the Technical University of Dortmund, points out that with other coronaviruses that cause normal colds, one to one and a half years are protected against a new infection on average. A natural infection is not comparable to a vaccine, yet the immune response is more efficient after a vaccine, says Watzl, who is also Secretary General of the German Society for Immunology. “So the hope is that vaccine candidates will give immunity for much longer.”
“Annoying, but manageable”
Whether antibodies, T cells, or a mixture of the two are important for immunity, cannot yet be answered, Watzl says. Adds immunologist Jacobs: “It is presumed that sterile immunity depends primarily on a large number of neutralizing antibodies, while the severity of the course is related to the T-cell response, so there is probably no ‘major’ in this context”.
Looking at vulnerable risk groups, for example in nursing homes, it is more important to have a vaccine that offers sterile vaccine protection for nurses and others who work intensively with risk groups, says Jacobs. Then they would probably have to get vaccinated more often. “For the general population, clinical immunity would be sufficient.”
Furthermore, at present it is not yet clear whether a vaccine will also protect against transmission of the pathogen. “If the antibody response is high, the likelihood of it occurring is very low,” explains Jacobs. However, with clinical immunity, there could still be a risk of spread; more studies should be done.
In general, according to immunologist Watzl, the vaccines would initially defuse the situation. “Even if the protection lasts for only two years, you could still get vaccinated,” he says. “That would be annoying, but manageable.” And Sars-CoV-2 would become another pathogen to be vaccinated against periodically. “But then we wouldn’t have a pandemic anymore.”
