A study published in The Lancet Infectious Diseases journal indicates that exposure to the virus may not guarantee future immunity Photo: AFP/File
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COVID-19 reinfection casts doubt on virus immunity: study

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By Patrick GALEY

Covid-19 patients may experience more severe symptoms the second time they are infected, according to research released Tuesday confirming it is possible to catch the potentially deadly disease more than once.

A study published in The Lancet Infectious Diseases journal charts the first confirmed case of COVID-19 reinfection in the United States -- the country worst hit by the pandemic -- and indicates that exposure to the virus may not guarantee future immunity.

The patient, a 25-year-old Nevada man, was infected with two distinct variants of SARS-CoV-2, the virus that causes COVID-19, within a 48-day time frame.

The second infection was more severe than the first, resulting in the patient being hospitalised with oxygen support.

The paper noted four other cases of reinfection confirmed globally, with one patient each in Belgium, the Netherlands, Hong Kong and Ecuador.

Experts said the prospect of reinfection could have a profound impact on how the world battles through the pandemic.

In particular, it could influence the hunt for a vaccine -- the currently Holy Grail of pharmaceutical research.

"The possibility of reinfections could have significant implications for our understanding of COVID-19 immunity, especially in the absence of an effective vaccine," said Mark Pandori, for the Nevada State Public Health Laboratory and lead study author.

"We need more research to understand how long immunity may last for people exposed to SARS-CoV-2 and why some of these second infections, while rare, are presenting as more severe."

Vaccines work by triggering the body's natural immune response to a certain pathogen, arming it with antibodies it to fight off future waves of infection.

But it is not at all clear how long COVID-19 antibodies last.

For some diseases, such as measles, infection confers lifelong immunity. For other pathogens, immunity may be fleeting at best.

The authors said the U.S. patient could have been exposed to a very high dose of the virus the second time around, triggering a more acute reaction.

Alternatively, it may have been a more virulent strain of the virus.

Another hypothesis is a mechanism known as antibody dependent enhancement -- that is, when antibodies actually make subsequent infections worse, such as with dengue fever.

The researchers pointed out that reinfection of any kind remains rare, with only a handful of confirmed cases out of tens of millions of COVID-19 infections globally.

However, since many cases are asymptomatic and therefore unlikely to have tested positive initially, it may be impossible to know if a given Covid-19 case is the first or second infection.

In a linked comment to The Lancet paper, Akiko Iwasaka, a professor of Immunobiology and Molecular, Cellular and Developmental Biology at Yale University, said the findings could impact public health measures.

"As more cases of reinfection surface, the scientific community will have the opportunity to understand better the correlates of protection and how frequently natural infections with SARS-CoV-2 induce that level of immunity," she said.

"This information is key to understanding which vaccines are capable of crossing that threshold to confer individual and herd immunity," added Iwasaka, who was not involved in the study.

© 2020 AFP

©2020 GPlusMedia Inc.


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A study published in The Lancet Infectious Diseases journal charts the first confirmed case of COVID-19 reinfection in the United States -- the country worst hit by the pandemic -- and indicates that exposure to the virus may not guarantee future immunity.

To be completely fair that is true for every other infectious disease, from measles to ebola. In medicine nothing is 100% true all the time.

Experts said the prospect of reinfection could have a profound impact on how the world battles through the pandemic

Of course, but only if it is something that happens with a certain frequency. If you observe one reinfection for every million cases that would not have a significative impact.

Vaccines work by triggering the body's natural immune response to a certain pathogen, arming it with antibodies it to fight off future waves of infection.

But it is not at all clear how long COVID-19 antibodies last.

That is not completely true, vaccines work by stimulating the immune response, including antibodies but also other parts of the system that can protect against future exposures. Antibodies are just the easiest to examine, not the only important part.

The real importance of studying these rare reinfections is because they let us understand better the infection and hopefully identify exactly what parts of the immune reaction are the most important to avoid complications.

The authors said the U.S. patient could have been exposed to a very high dose of the virus the second time around, triggering a more acute reaction.

Alternatively, it may have been a more virulent strain of the virus.

Or the patient could have some natural susceptibility because of genetic variation, or low levels of some specific lymphocytes, or some comorbidity that was not identified the first time that lowered temporarily his immune system. As long as the reinfections are very limited it is more likely that the specific situation of the patient is responsible than a viral factor.

Another hypothesis is a mechanism known as antibody dependent enhancement -- that is, when antibodies actually make subsequent infections worse, such as with dengue fever.

Extremely unlikely, like astronomically so.

ADE depends on having serotypes of the infection, that means that antibodies against one strain are not useful against a different strain (for Dengue there are 4 serotypes, so a completely healthy person can get infected 4 times with the disease) For COVID there is only one serotype identified yet.

Also, if ADE was the cause you would observe clusters of reinfections with very severe symptoms, because people infected once would not have any protection against the different serotype of the virus and many of those reinfected people would have very severe symptoms, even if they were young adults without comorbidities, that would be like a huge red alert if it happened anywhere in the world.

However, since many cases are asymptomatic and therefore unlikely to have tested positive initially, it may be impossible to know if a given Covid-19 case is the first or second infection.

For any specific case this is true (unless specialized tests are done to search for differences in neutralization levels of the antibodies and curves of elevation on IgG and IgM), but in a community level epidemiological analysis would give very strong hints of this happening. This kind of data is relatively easier to get, so many researchers are using it to find out unusual patterns or outliers that could be of interest. So for now the possibility of reinfections being common remains very low.

"This information is key to understanding which vaccines are capable of crossing that threshold to confer individual and herd immunity," added Iwasaka, who was not involved in the study.

And also to understand how long the immunity for the natural infection lasts.

4 ( +7 / -3 )

5 cases worldwide! Appears to be a very rare event.

And also to understand how long the immunity for the natural infection lasts.

Those who recovered from the 1st SARS CoV (17 years ago) still have the memory lymphocytes that would protect them from a second attack. So far, it appears to also be the case for SARSCoV2, but its too soon to know for sure. Time will tell.

-2 ( +0 / -2 )

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2 ( +3 / -1 )

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1 ( +2 / -1 )

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