19 – What is known so far about reinfections and immunity against the coronavirus

Recently, several reports were made about individuals who were infected with the new corona virus for the second time. What does this say about immunity and the vaccine search?

What is known about reinfections with the coronavirus?

Since the new coronavirus has been circulating around the world, it has been puzzled as to whether and when someone could get Covid-19 again after a corona infection – an important question also with regard to the requirements for vaccines. As early as spring, some cases became known in which the coronavirus could be detected again a few weeks later after a negative test. In these cases, researchers assume different scenarios: the virus could have stayed in the body and the disease could have flared up again later – or the tests were misleading because dead viral material could have been detected.

Now there have been reports from some patients – for example in Belgium, the Netherlands, the USA, Ecuador and Hong Kong – who have contracted the virus again weeks to months after being infected with Sars-CoV-2. These are definitely reinfections: As the virologist and advisor to the Dutch government, Marion Koopmans, announced, the genetic code of the Dutch patient – a kind of fingerprint of the virus – differs significantly from the first in the second infection. That speaks against a flare-up of the first infection, she said on Dutch radio.

Genetic fingerprint changes

Another genetic fingerprint was found in the newly ill patient from Belgium. She was sick again three months after the first infection. Shortly before, the University of Hong Kong reported on a man who was infected again after four and a half months – different virus sequences were found in him than in the initial infection. It was the same with one Man in the US state of Nevada and one Ecuadorianer, as reported by researchers from both countries.

How does a reinfection work?

So far there are no research results on this, as only these three cases of reinfection have been reliably documented. In the case of the Hong Kong man, it is known that, according to the university, he did not show any symptoms with the second infection. In the case of the patient in Belgium, the virologist Marc Van Ranst speaks of mild symptoms. In the Netherlands it concerns an elderly patient with a weak immune system, details of the course of the disease are not known. It could be that the course is at least easier with a second infection – or that you are no longer contagious, suspects Carsten Watzl, Secretary General of the German Society for Immunology.

The individual cases from the USA and Ecuador currently speak against this. The 25-year-old American had initially tested positive for Sars-CoV-2 in mid-April after milder cold symptoms and diarrhea. At the end of May he was tested positive again – this time with fever, headache and cough, and he also had to be ventilated from time to time. The man from Ecuador had only mild symptoms when he was infected for the first time in May, and in August the disease was moderately severe.

How long are you immune after a corona infection?

This question is still largely unanswered. The Dlf program “Forschung aktuell “reports on new studies by Harvard Medical School and the University of Toronto that focus on antibodies against the coronavirus. More than 300 infected people were examined for the studies. The result: Antibodies were in the blood of most of the infected people and also The researchers found the greatest amount of antibodies in the patients examined two to four weeks after infection, after which the amount of antibodies decreases.

After three months, antibodies were still present in almost all infected people, and in some even after six months, albeit in lower concentrations.
However, it is difficult to derive an answer to the question of whether and how long the immune protection persists. Because in addition to the antibodies, other factors such as the general strength of the immune system, which varies from person to person, play an important role in protection against the pathogen. It is still possible that the duration of immunity differs from person to person, as the Robert Koch Institute says.

No antibodies in proven infected people

The answer after natural immune protection is made more difficult by the fact that in some people who have been proven to be infected, no antibodies at all are found, as a study by the Jena University Hospital shows. In the former Corona quarantine Neustadt am Rennsteig, no antibodies against the pathogen could be detected in around half of the infected. A study by the Lübeck health department had also come to the conclusion that only 70 percent of those infected had formed antibodies, while 30 percent did not.

What role do T helper cells play in defense?

But it’s not just antibodies that fight an infection. So-called T helper cells also play an important role, since they can remember for years which pathogens the body has successfully fought. However, tests on these immune cells are significantly more complex than antibody tests, such as Gerard Krause from the Helmholtz Center for Infection Research Deutschlandfunk said.

In a small study, researchers at the Karolinska Institute in Stockholm tested the blood samples of 2,000 people in the Swedish capital for evidence of T-cell immunity to Sars-Cov-2. They saw that some people did not have antibodies, but still showed T-cell immunity – especially people who had only very mild or hardly detectable symptoms. The actual percentage of people who have already had a corona infection and are probably immune for the time being could therefore be higher than antibody studies suggest. This was also recently communicated in relevant studies.

What does this mean for vaccine development?

According to our research department, when an immune reaction is mentioned in vaccination studies, it refers to antibody production. It is unclear from what level an immunity is achieved and how long it lasts. In addition, it is only clear so far for the vaccine candidate from the University of Oxford that the vaccine also produces suitable T memory cells – but that would be quite relevant for long-term immunity. The DLF research team has put together information on the status of vaccine research here.

What are the benefits of plasma treatment with antibodies?

In the USA, the treatment of Covid-19 sufferers with plasma from patients who have already recovered has now been permitted with an emergency permit. The blood plasma contains antibodies that are supposed to help the sick – a process that has been practiced for over a century. So far there have been indications with regard to Covid-19 that seriously ill patients survive somewhat more often when they are given plasma with antibodies than without them. The results are not clear, because the patients usually received other drugs in addition to the plasma. An official approval of the treatment is therefore still pending in the USA. Critics accuse US President Trump of having initiated the emergency approval mainly because of the presidential election campaign.

DLF science correspondent Volkart Wildermuth has put together further information on immunity to the new coronavirus here.

(Stand: 10.10.2020)

Further articles on the coronavirus

We have a News blog created. In view of the large amount of information, this provides an overview of the most important current developments.

Numbers and dates

+ Current developments: Figures on the coronavirus in Germany (Stand: 22.11.)
+ Location in Germany: What does the rapid increase in new infections and the incidence value mean? (Stand: 22.10)

Test and protection

+ Protection: This is how the vaccination against the coronavirus should be organized (Stand: 20.11.)
+ Tests for the coronavirus: When, where and how (Stand: 29.10.)
+ How useful are mass tests for the whole population? (Stand: 15.11.)
+ Corona infection events: How reliable are the tests? (Stand: 18.11.)
+ Treatment: That is how far vaccine research against the coronavirus is (Stand: 16.11.)
+ Remdesivir and Co: How far is the search for drugs against Covid-19? (Stand: 16.10.)
+ Infection: What is known so far about reinfections and immunity against the coronavirus? (Stand: 10.10.)
+ Hospitals: What the increase in corona infections means for you (Stand: 14.11.)

Contagion and Transmission

+ Transmission: How infectious are children? (Stand 17.11.)
+ Transmission: What role do aerosols play (Stand: 10.10.)
+ Face masks: What you should know about protective masks (Stand: 29.10.)
+ Excess mortality: How deadly is the coronavirus really? (Stand: 14.11.)
+ Travel warning: The current list of risk areas (Stand 13.11.)

You can also find the Dlf news on Twitter at: @DLFNews.

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