So you start to feel bad. Your throat hurts, your head hurts, you feel tired and you have developed a cough.
You recently had COVID-19, but as we now know, it’s possible to be reinfected.
But how sick will you be the second time around?
Although your symptoms are probably less severe, in some cases they may be worse. Here’s what we know so far.
After COVID, you don’t need to test for 12 weeks
Fluent guidelines define you as a “resolved case” for 12 weeks after end COVID isolation.
If you develop COVID-like symptoms during these 12 weeks, you do not need to be tested.
The science behind this 12-week delay is evolving.
The original idea was that if you have recovered from COVID and have a healthy immune system, you will have developed immunity against reinfection. And it will protect you for at least 12 weeks.
As the number of cases in Australia increases, reports of reinfections are also on the rise. And it is likely that reinfection will occur sooner than expected.
What happens in our body?
For a person to be able to fight re-infection with a virus, they must have developed a protective immune response.
Two main factors decide whether a person will have a protective immune response:
- How long does a person’s immune memory last
- How well that memory recognizes the virus, or a slightly different virus.
Immune memory is made up of many critical 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).
Evidence so far suggests that immune memory for SARS-CoV-2, the virus that causes COVID, lasts for month or even years regarding B cells and the antibodies they produce.
In the same way, current evidence shows that memory T cells can last more than a year.
This means that for a healthy person, the immune memory for SARS-CoV-2 appears to last for a year, against reinfection with the exact same virus.
So why the reinfections?
A clear explanation for reinfection is that the virus is mutating.
SARS-CoV-2 replicates rapidly and in doing so creates replication errors. We call these errors mutations. Over time, mutations accumulate and a new sub-variant emerges.
Since the start of the pandemic, we have seen the Wuhan parent strain mutate into Alpha, Beta, Delta and now Omicron.
The current theory is that immunity against one variant may not provide sufficient protection against another.
Data so far suggest that the Omicron variant is better at immune evasion than its predecessors.
This means that Omicron “escapes” the immune memory created by SARS-CoV-2 infections from other variants such as Delta, Beta or Alpha.
Emerging data now shows that subvariants of Omicron can also evade immunity from a previous Omicron variant. This means that a person might be able to get re-infected with Omicron.
A small, not yet peer-reviewed study in denmark found that in unvaccinated individuals, reinfection with Omicron BA.2 is possible after a primary infection with Omicron BA.1. Despite this finding, the study also concluded that reinfection rates were low and therefore rare.
With the approach of winter and the increase in the number of cases, we are also seeing the emergence of new subvariants such as BA.4 and BA.5.
First evidence shows these new subvariants are even better at evading immune memory than the BA.1 Omicron parent.
What about gravity?
For those who become reinfected, the severity of illness appears to be softer and less likely to result in hospitalization. This is likely because the immune memory can recognize at least some of the reinfecting virus.
However, it is difficult to measure the severity of the disease on a population level). A systemic review case studies have shown that while some second infections were milder, this was not the case in all cases. Some reinfections have resulted in worse outcomes, including death. (During this study period, one of the original strainsB.1, caused most primary infections, with reinfections caused by Alpha or Beta variants.)
But while Omicron seems to cause more reinfections than other variants, there is not enough hard 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 that reinfection is less severe.
We also know from several studies that vaccination brings protection against reinfectionincluding in previously infected people who then receive subsequent vaccines.
All the more reason to boost
A recent study which has not yet been peer reviewed, immunity against the Omicron BA.1 variant drops approximately 7.5 times with the newer Omicron BA.4 and BA.5 variants. This means that the antibodies you produce from a BA.1 infection, which are able to detect and neutralize the BA.1 virus, are 7.5 times less able to recognize and neutralize BA.4 and BA. 5 than BA.1.
This study also found that vaccination and natural exposure to Omicron BA.1 provided five times greater protection to Omicron BA.4 and BA.5 than immunity to natural exposure to BA.1 alone.
Data also shows the strongest protective immunity comes from a mixture of triple vaccination and natural infection.
A complementary study found this type of hybrid immunity protects better against reinfection and hospitalization than natural immunity alone, highlighting the importance of vaccination and vaccine boosters.
So the question remains: if our immune memory lasts for a year, but is too specific to recognize new variants, will we need a new vaccine every year?
Time will tell us.
Lara Herrero, Head of Research in Virology and Infectious Diseases, Griffith University
This article is republished from The conversation under Creative Commons license.
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