Our national 6-month coronaversary has arrived. It’s now been 6 months since our world turned upside down. The world is not the same place it was in January, a statement that is as obvious as it is disconcerting. It’s funny how something can seem like it was just yesterday and a lifetime ago at the same time. I think this summarizes the past 6 months:

  • Do you get the coronavirus from Mexican beer?
  • Where’s Wuhan?
  • There’s no toilet paper!
  • There’s nowhere to get tested.
  • You don’t need to wear a mask.
  • Fauci is our savior!
  • Hydroxychloroquine will save us all! Anyone who disagrees is part of the conspiracy.
  • Fauci doesn’t know anything!
  • You can inject clorox?
  • Everyone needs to wear a mask!
  • You can’t tell me to wear a mask!
  • Does anyone remember sports?
  • It’s all gone, let’s open up the bars and restaurants!
  • We shouldn’t have done that.
  • I’m getting a puppy!
  • I shouldn’t have done that.
  • Opening up schools is irresponsible unless it’s not.
  • I need an air hug.

Some of the most common lingering questions that have contributed to uncertainty over the course of the pandemic are those related to immunity. If you get infected, how long are you protected from reinfection? Are you protected at all? Early on in the pandemic there could only be speculation based on knowledge of other coronaviruses. For some of these viruses immunity lasts less than a year while for others it lasts longer. How long people who have recovered from infection remain immune is a hugely important question. It impacts issues of herd immunity and vaccine effectiveness. The problem is that the only way to know is to wait and see.

A quick review on herd immunity. Herd immunity happens when a large part of the population (i.e. ‘the herd’) develops immunity to a virus. This can happen either because the herd gets vaccinated or are immune after recovering from an infection. When a large part of the herd is immune, the virus has fewer people it can infect. This means there are fewer people that can spread the virus. At some point there are so few possible targets for the virus that it can die out altogether. The nice thing about herd immunity is that it protects those who are high risk or who cannot get vaccinated – if there’s less virus around there’s less risk to them even if they are not immune themselves.


With some coronaviruses immunity is very short lived, lasting less than a year. As people lose their individual immunity, herd immunity would also be lost.


Every virus has a different percentage of people necessary to become immune to create herd immunity depending on factors related to the viruse’s contagiousness and virulence (how sick it makes people). Unfortunately, this percentage is not known for sure with SARS CoV-2 and there have been wide ranging estimates of numbers between 40 and 80%.

Over the past months many people have dramatically relaxed their social distancing and masking in areas previously hard hit by the virus. One justification for this has been that, since there have not been increases in the number of cases for several weeks, there must be herd immunity. While I so greatly want to believe the proponents of this hypothesis are correct, there are many reasons to believe they are not.

Even if these locations have reached herd immunity there is reason to worry that the herd immunity will not last. The first concern is waning immunity. With some coronaviruses immunity is very short lived, lasting less than a year. As people lose their individual immunity, herd immunity would also be lost. Second is the concern for reinfection, perhaps from different strains of the virus or from an inadequate initial immune response to the infection. Reinfection has been a topic of recent concern.

Reinfection has been reported multiple times over the past few months but it was very difficult to prove that it was a true reinfection. For the most part, these cases were believed to be the result of testing errors and not true reinfections. None of the reports of reinfection were confirmed with rigorous testing (for more of an explanation of the views on this issue back in April, read this).

Things changed somewhat recently when there was a report of reinfection that was different. This time the researchers carefully sequenced the DNA of the virus from both infections and found genetic differences in the two samples. This confirms a true reinfection. Subsequently, there have been other reports of reinfection using the same methodology confirming it as a reality.

The existence of reinfection is obviously concerning. It would mean that herd immunity would be harder to achieve and that people may require multiple vaccine boosters to achieve longer lasting immunity.


It would mean that herd immunity would be harder to achieve and that people may require multiple vaccine boosters to achieve longer lasting immunity.


While concerning, it is not yet cause for panic. The fact that after several million worldwide infections we have had so few confirmed cases makes it possible that these cases of reinfection are outliers and have features that won’t apply to the tens of millions of other people who have already recovered from COVID-19. There are also reasons to believe that reinfection could be milder (although the individuals would still be contagious).

The pandemic is baffling and frustrating for all of us but at least it’s consistent in this regard. Hopefully most of you are growing accustomed to the uncertainty. If we continue to do this right we will not need to lock ourselves in our homes again. Doing it right means staying strong with our masking, distancing, isolation (when infected), and quarantine (when exposed). We can hope for herd immunity but hope is not a good strategy. This is especially true as we send kids back to school.

It’s been six months of this misery and I have seen too many people die to not err on the side of caution. We’re all tired but it will probably be another six months before our international mask burning vaccine party. How that six months goes down is up to you.

One thought on “Maybe you can get COVID twice

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