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Infectious Diseases

Updated 15 September 2020

Three things scientists still need to learn about Covid-19 reinfections

The possibility of reinfection has sparked questions about whether there can be long-term Covid-19 immunity, and what implications that would have for a vaccine.

  • The latest reports on SARS-CoV-2 reinfections have sparked concern and fear
  • However, researchers have identified three key questions that need to be answered before assumptions can be made
  • This includes what implications reinfections could have for vaccine development

On 24 August 2020, researchers in Hong Kong reported what appeared to be the first confirmed case of true Covid-19 reinfection. The patient is a 33-year-old man who tested positive for SARS-CoV-2 late in March. Four months later, he tested positive again.

Since then, there have been very few reported cases of reinfections. Earlier in the outbreak, it was debated whether such cases were the result of continuous viral shedding, or actual reinfection.

This has spurred scientists to question whether these cases of reinfection can tell us more about the immune system vs. Covid-19, and what that would mean for successful vaccine development.

The questions that scientists want answered 

As more and more information started surfacing regarding patients testing positive more than once, an article in Nature identified three questions that researchers should answer to determine the impact of these reinfections at population level.

1. How often does reinfection occur?

While cases of patients testing positive twice occurred earlier during the outbreak, researchers have established that the recent cases were true confirmed reinfections instead of a continuation of the first infection.

A study published in Clinical Infectious Diseases used a method known as genome sequencing to determine the viral strains from both first and second infections. While this study focused on two cases of reinfections that definitely occurred from a different source compared to the first infection, it’s too small to tell exactly how many reinfections could occur.

According to virologist Thomas Geisbert from the University of Texas Medical Branch in Galveston, a lot more information is needed before we can establish how common reinfections are. A few reinfections in 26 million known cases worldwide is not yet any reason to worry, he stated.

2. How severe are reinfections?

According to reports, the patient from Hong Kong didn’t display any symptoms from the second infection with SARS-CoV-2. But, according to virologist Jonothan Stoy, this doesn’t mean that we should rest on our laurels about second infections, and it is too difficult to draw conclusions from just one case, as the effects of Covid-19 differ from person to person.

The way symptoms play out during reinfections could tell us more about the immune system’s so-called memory response to the coronavirus, and that may influence vaccine development.

According to experts, reduced symptoms during a reinfection means that the immune system is reacting as it should, but if symptoms generally get worse during a reinfection, this may mean that rogue immune responses may be making things worse, rather than better.

More data on reinfections should establish whether symptoms generally get worse or better during reinfection, and shed more light on what exactly the immune system is doing when confronted with the virus for a second time.

3. What do reinfections mean for vaccine developments?

According to the article published in Nature, the easiest vaccines to develop were against viruses that lead to lasting immunity, such as measles.

But this doesn’t necessarily mean that we are doomed with Covid-19, stated Richard Malley, a paediatric infectious-disease specialist at Boston Children’s Hospital in Massachusetts.

Some vaccines require booster shots, and that may be the case for Covid-19.

“It shouldn’t scare people,” Malley stated. “It shouldn’t imply that a vaccine is not going to be developed or that natural immunity to this virus can’t occur, because we expect this with viruses.”

The more researchers learn about reinfections, the more researchers will know about vaccine development. If they know, for example, that reinfections happen because antibodies drop below a certain level, this may help vaccine developers look into strategies such as booster shots.

There are concerns that vaccines may only reduce symptoms and not completely halt Covid-19, according to Malley. This could put more vulnerable people at risk, as asymptomatic carriers may still spread the virus. 

Malley stated in Nature that, for this reason, he would like to see the level of viral shedding when people get reinfected with Covid-19.  “We need to understand that better following natural infection and vaccination if we want to get out of this mess,” he said.

READ | New research shows early signs that Covid-19 may trigger longer-term immunity 

READ | Understanding immunity and what it means for vaccines 

READ | Why check-ups for Covid-19 recoveries are important 

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