So you start to feel unwell. Your throat hurts, your head hurts, you feel tired and you have to cough.
You have recently had COVID, but as we now know, it is possible to become re-infected.
But how sick do you get the second time?
While your symptoms are likely to be less severe, in some cases they can be worse. This is what we know so far.
After COVID you don’t have to test for 12 weeks
Current guidelines define you as an “approved case” for 12 weeks after the end of COVID isolation. If you get COVID-like symptoms in those 12 weeks, you don’t need to be tested.
The science behind this 12 week time frame is evolving. The original idea was that if you have recovered from COVID and you have a healthy immune system, you have developed immunity to reinfection. And with this you are protected for at least 12 weeks.
As the number of cases in Australia increases, so do the reports of reinfections. And it’s likely that reinfection is happening faster than we first thought.
What happens in our body?
To fight reinfection with a virus, a person must have developed a protective immune response.
Two main factors determine whether a person will have a protective immune response:
1) how long a person’s immune memory lasts
2) how well that memory recognizes the virus, or a slightly different virus.
Immune memory is made up of many crucial parts, each of which plays a role in the protective army of your immunity. The biggest players in protective immunity memory are your B cells (which mature to make antibodies) and your T cells (which destroy virus-infected host cells).
So far, the evidence suggests that immune memory for SARS-CoV-2, the virus that causes COVID, lasts for months or even years when it comes to B cells and the antibodies they produce.
Likewise, current evidence shows that the memory T cells can last more than a year.
This means that for a healthy person, the immune memory for SARS-CoV-2 seems to last a year, against reinfection with the exact same virus.
So why the reinfections?
A clear explanation for reinfection is that the virus mutates. SARS-CoV-2 replicates quickly, making replication errors. We call these errors mutations. Over time, the mutations pile up and a new subvariant is born.
Since the start of the pandemic, we have seen the parental Wuhan tribe mutate to Alpha, Beta, Delta and now Omicron.
The current theory is that immunity from one variant may not provide adequate protection against another.
Data to date suggests that the Omicron variant is better at immune escape than its predecessors. This means that Omicron “escapes” the immune memory created by SARS-CoV-2 infections of other variants such as Delta, Beta or Alpha.
Emerging data now shows that subvariants of Omicron can also escape immunity from a previous Omicron variant. This means that a person could potentially get an Omicron reinfection.
A small, yet too peer-reviewed study from Denmark showed that re-infection with Omicron BA.2 is possible in unvaccinated people after a primary infection with Omicron BA.1. Despite this finding, the study also concluded that reinfection rates were low and therefore rare.
Now that winter is approaching and the number of cases is increasing, we are also seeing the emergence of new sub-variants such as BA.4 and BA.5. Early evidence shows that these new subvariants are even better at escaping immune memory than the parental BA.1 Omicron.
What about the seriousness?
For those who get a reinfection, the severity of the disease appears to be milder and less likely to require hospitalization. This is probably because the immune memory can recognize at least part of the reinfecting virus.
However, it is difficult to measure disease severity at the population level. A systemic review of case studies found that while some second infections were milder, this was not the case in all cases. Some reinfections resulted in worse outcomes, including death. (During this study period, one of the original strains, B.1, caused the most primary infections, with reinfections caused by alpha or beta variants.)
But while Omicron appears to cause more reinfections than other variants, there is not enough robust data to draw firm conclusions about the severity of reinfection with Omicron or other variants.
What we know for sure is that we need more data from more people to say reinfection is less serious.
We also know from several studies that being vaccinated offers protection against reinfection, including in previously infected people who subsequently receive subsequent vaccines.
Another reason to get a boost
A recent peer-reviewed study found that the immunity of the Omicron BA.1 variant drops about 7.5-fold with the new Omicron BA.4 and BA.5 variants. This means that the antibodies you make from a BA.1 infection, which can detect and neutralize the BA.1 virus, are 7.5 times less able to recognize and neutralize BA.4 and BA.5 then BA.1.
This study also found that vaccination plus natural exposure to Omicron BA.1 gave five times more protection to Omicron BA.4 and BA.5 than the immunity against natural exposure to BA.1 alone.
Data also show that the strongest protective immunity comes from a combination of triple vaccination and natural infection.
A further study found that this type of hybrid immunity protects against both reinfection and hospitalization better than natural immunity alone, highlighting the importance of vaccination and vaccine boosters.
So the question remains: If our immune memory lasts a year, but is too specific to recognize the new variants, do we need a new vaccine every year? Time will tell.
Lara Herrero is a research leader in virology and infectious diseases at Griffith University. This piece first appeared on The conversation†