An emerging trend of reinfections
The TLDR: There have been a flurry of reports of people contracting Covid for the second time from around the world: Hong Kong, Belgium, Netherlands and—closer to home—Telangana! So is this reason to worry? No, but it suggests that neither an infection nor a vaccine can provide lifelong immunity. Most importantly: we don’t know if a reinfected person can spread the disease.
Tell me about these cases
At least three of these are the first confirmed cases of reinfection. Until now, there were suspected cases, but there was no scientific evidence. Doctors had not sequenced the genes of the virus in each case to confirm that the positive Covid test was the result of a new infection, and not due to the viral residue of the old one.
- Hong Kong: A 33-year old man got a mild case of Covid around the end of March—and recovered fully. But when he underwent mandatory screening at the airport, he tested positive again.
- Belgium: A woman in her 50s was infected in early March. Her body did not produce a lot of antibodies the first time around. She has tested positive again after displaying mild symptoms.
- Netherlands: Not much is known about this patient other than she is elderly and has a weak immune system.
- Telangana: Two medical professionals—age and gender unknown—have tested positive after two months. They are entirely asymptomatic. But scientists have not yet confirmed that these are indeed two different strains—and therefore reinfections.
And they got sick all over again?
Yes, but with a different strain of the virus—and almost all had zero or mild symptoms the second time around.
What does that tell me?
The virus mutates: Experts now know that there are at least six strains of the original virus. But none of the mutations are more serious than the others—though some may be more infectious. Mutation is normal virus behaviour—which is why we get a different strain of flu each year. And all things considered, the coronavirus appears to be less volatile. As one Belgian virologist puts it: “We would have loved the virus to be more stable than it is, but you can’t force nature.”
But our body remembers: When we become infected with a virus, our body produces antibodies and memory cells (i.e. T or B cells). The antibodies disappear within a few months. This is true for any kind of infection. But the memory cells “remember” the virus. Therefore, our body responds faster and more effectively if/when it returns—even if it is a different strain. This is the likely reason why the second infection produces zero or only mild symptoms.
The Conversation notes: “Our bodies do not become impervious to viruses when we recover from infection. Instead, in many cases, they become inhospitable hosts.” Or as another expert put it, “[T]his is a textbook example of how immunity should work.”
Immunity isn’t forever: Reinfections make clear that simple ‘herd immunity’ won’t protect us. This is where the vast majority of a population becomes immune after becoming exposed to the virus (we explained the concept here). Dr Lance Pinto lays it out:
“If reinfection is a real possibility, then you’ll have multiple spikes until you have a vaccine. Same with herd immunity. I’m not saying it can’t be achieved—mathematically, let’s say theoretically the possibility of reinfection occurs after a year. In that year, you achieve herd immunity and then the transmission is over. That is, unless someone comes from outside and reintroduces the infection. So, perhaps, lasting herd immunity cannot happen through infection, and only through vaccination.”
Ergo: A vaccine is a must!
But will a vaccine work? Some scientists are worried that reinfections may be bad news for any potential vaccine. A vaccine essentially injects some part of the virus into the body to trigger an immune response (antibodies, T and B cells etc.)—which ought to protect us from future infections. But it may not be able to protect us for very long if Covid immunity lasts only a few months, as one doctor told AFP:
"'It suggests that previous infections are not protective. It also raises the possibility that vaccinations may not provide the hope that we have been waiting for.’ If antibodies don't provide lasting protection, ‘we will need to revert to a strategy of viral near-elimination in order to return to a normal life.'"
Or are vaccines different? Others argue that these reinfections make an even stronger case for vaccines.
- One reason: vaccines are designed to trigger stronger immune responses than an infection.
- The other reason: we don’t know as yet if a reinfected person can spread the disease. But vaccines protect against that possibility.
- Virologist Jacob John says, “It does not work in the same way because a vaccinated person does not spread the disease, while an infected person passes it on to others in the initial days at least.”
Most agree that there won’t be a one-shot vaccine as in the case of polio. As with many other diseases, we will have to get booster shots at regular intervals. We don’t know enough about the virus right now to determine how often that will be.
The bottomline: Thus far, we’ve only confirmed a handful of reinfections. The bigger problem is that there may be many more that have gone undetected. If the second bout is mild or asymptomatic then the once-infected person—who also assumes they are now immune—will most likely not get re-tested. This again increases the risk that they will spread the disease.
And that’s the big takeaway here: even recovered patients have to take the exact same precautions as everyone else, as Pinto explains:
“Look, we’ve never said ‘okay, now you’ve recovered from Covid. You can remove your mask, you can live your life.’ When patients who recovered from Covid ask us, we’ve always said, ‘we don’t know.’ But now, nobody can, or should, make the argument that ‘I have the strongest antibodies so I don’t have to wear a mask,’ especially now that workplaces are opening up. Caution is advised no matter if you’re recovered from Covid19 or not.”
Big point to note: India has just launched a nationwide serological survey to check how many children have been exposed to the virus. The results will be a key factor to determine whether we reopen schools: “High prevalence among children and adolescents would support school opening, while low prevalence would imply greater risk.” But that assumption of “herd immunity” doesn’t hold if reinfections are indeed common.
Reading list
- AFP via Yahoo News has the best reporting on the Hong Kong case. Read The Print for details on Telangana, and Deutsche Welle for the cases in Europe.
- The Conversation via The Guardian explains why reinfections are not a great cause for alarm.
- The Swaddle has an excellent must-read interview with Dr Lance Pinto on the broader implications.
- BBC News explains how T cells work.
- The Telegraph has more on the serological survey.
- Also see: our explainer on how vaccines work and the race to develop one.
- A related read: The US Center for Disease Control has mystifyingly declared that people who do not have symptoms do not need to be tested—even if they were in contact with a Covid case.