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COVID-19What we know so far about reinfections and immunity to the coronavirus

Blood samples can be tested for antibodies against the novel coronavirus. (photo alliance / Marijan Murat / dpa)

Recently, there were several reports of individual people being infected with the new corona virus for the second time. What does this say about immunity and vaccine seeking?

What is known about coronavirus reinfections?

Since the new coronavirus has been circulating around the world, the question is whether and when someone could get Covid-19 again after a corona infection – an important question also with regard to the requirements for vaccines. A few cases were already known in the spring in which the corona virus 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 flared up later – or the tests were misleading because dead viral material could have been detected.

Now, there have been reports of some patients – for example in Belgium, the Netherlands, the US, Ecuador and Hong Kong – who contracted the virus again weeks to months after being infected with Sars-CoV-2. These are certainly re-infections: as the virologist and adviser 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 one 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 also found in the recently ill patient from Belgium. Three months after the first infection, she was ill again. Shortly before, the University of Hong Kong reported on a man who was reinfected after four and a half months – different virus sequences were found in him than in the first infection. It was the same with a guy in Nevada and a Ecuadorian, as reported by researchers from both countries.

How does reinfection work?

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

Individual cases from the US 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 a fever, headache and cough, and he also had to be ventilated from time to time. The Ecuadorian had only mild symptoms when he was first infected in May, and the disease was moderately severe in August.

How long are you immune after a corona infection?

This question is still largely unanswered. The DLF “Research News” program reports on new studies from Harvard Medical School and the University of Toronto targeting antibodies against the coronavirus. More than 300 infected people were examined for the studies. The result: antibodies were detectable in the blood and also in the saliva of most infected people. The researchers found most antibodies in the patients studied two to four weeks after infection. The amount of antibody then decreases.

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

No antibodies in proven infected people

The answer to natural immune protection is complicated by the fact that some people who have been shown to be infected have no antibodies at all, a study from Jena University Hospital found. In the former Corona quarantine Neustadt am Rennsteig, no antibodies against the pathogen could be found in about half of those infected. A survey by Lübeck’s health department had also concluded 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 infection. So-called T helper cells also play an important role, because over the years they can remember which pathogens the body has successfully fought against. However, tests on these immune cells are significantly more complex than antibody tests, such as Gerard Krause of the Helmholtz Center for Infection Research said on Deutschlandfunk.

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

What does this mean for the development of vaccines?

According to our research department, when an immune response is mentioned in vaccination studies, it refers to the production of antibodies. It is unclear from what level an immunity is reached and how long it lasts. Moreover, it is so far only clear to the vaccine candidate at the University of Oxford that the vaccine also suitable memory T cells produce – but that would be quite relevant for long-lasting immunity. The editorial staff of DLF Research News has gathered information about the status of vaccine research here.

What are the benefits of plasma antibody treatment?

In the US, treatment of Covid-19 patients with plasma from already recovered patients is now permitted with an emergency permit. The blood plasma contains antibodies that are supposed to help the sick – a procedure that has been used for more than a century. So far, with regard to Covid-19, there are indications that critically ill patients survive slightly more often on administration of plasma with antibodies than without. The results are not clear because the patients usually received other drugs in addition to the plasma. Official approval of the treatment is still pending in the US. Critics accuse US President Trump of initiating the emergency clearance, mainly because of the presidential campaign.

DLF science correspondent Volkart Wildermuth has gathered more information about immunity to the new coronavirus here.

(Status: 10.10.2020)

Further articles about the coronavirus

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

Figures and dates

+ Current developments: Figures about the coronavirus in Germany (from November 22)
+ Situation in Germany: what does the rapid increase in new infections and the incidence value mean? (Status: 22/10)

Test and protection

+ Protection: this is how the vaccination against the coronavirus should be organized (status: 20.11.)
+ Tests for the coronavirus: when, where and how? (Status: October 29)
+ How useful are mass testing to the entire population? (As of November 15th)
Corona infection: how reliable are the tests? (Status: November 18)
+ Treatment: now is vaccine research against the coronavirus (from November 16)
Remdesivir and Co: How Far is the Search for Drugs for Covid-19? (From October 16)
+ Infection: what do we know so far about re-infections and immunity to the coronavirus? (Status: 10.10.)
+ Hospitals: What the Increase in Corona Infections Means for Them (Starting Nov. 14)

Contamination and transmission

Transmission: How Contagious Are Children? (As of November 17th)
+ Transfer: what role do aerosol cans play (from 10.10.)
+ Face Masks: What You Need to Know About Protective Masks (Starting October 29)
+ Over-mortality: how deadly is the coronavirus really? (As of November 14)
+ Travel alert: the current list of risk areas (as of November 13)

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

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