Did you get COVID again?  Your symptoms may be milder, but this is not always the case

Did you get COVID again? Your symptoms may be milder, but this is not always the case

The immune memory from SARS-CoV-2 may last for months or even years. credit: shutterstock

So you started to feel unwell. Your throat hurts, your head hurts, you feel tired and you have a cough.

You recently had COVID but as we now know, it is possible to get infected again.

But how sick are you the second time around?

While your symptoms will likely be less severe, in some cases they may get worse. Here’s what we know so far.

After COVID, you will not need to be tested for 12 weeks

Current guidelines define you as “case cleared” for 12 weeks after ending COVID isolation. If you develop COVID-like symptoms within 12 weeks, you do not need to be tested.

The science behind this 12-week time frame is developing. The original idea was that if you recover from Covid, and have a healthy immune system, you will have developed immunity to infection again. This will protect you for at least 12 weeks.

As case numbers increase in Australia, so are reports of infection cases. It is likely that the infection will occur again sooner than we initially thought.

What is happening?

For a person to resist re-infection with any virus, they must have developed a protective immune response.

There are two main factors that determine whether a person will elicit a protective immune response:

  1. How long does a person’s immune memory last?
  2. How well that memory recognizes the virus, or a slightly different virus.

Immune memory is made up of many important parts, each of which plays a role in the immune system’s protective army. The biggest players in the memory of protective immunity are B cells (which mature to produce antibodies) and T cells (which destroy virus-infected host cells).

So far, evidence suggests that the immune memory of 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.

Similarly, current evidence shows that memory T cells can last for more than a year.

This means that for a healthy person, the immune memory for SARS-CoV-2 appears to last up to a year, against re-infection with the exact same virus.

So why re-infection?

One obvious explanation for reinfection is that the virus is mutating. SARS-CoV-2 replicates rapidly and causes replication errors. We refer to these errors as mutations. Over time, mutations accumulate and a new subtype is born.

Since the beginning of the epidemic, we’ve seen the parental Wuhan strain switch to alpha, beta, delta and now omicron.

The current theory is that immunity to one variant may not provide adequate protection from another variant.

Data to date indicate that the omicron variant is better at immune escape than its predecessors. This means that Omicron “escapes” the immune memory generated by SARS-CoV-2 infection from other variants such as delta, beta or alpha.

Emerging data now show that omicron sub-variants can also evade immunity from a previous omicron variant. This means that a person may be able to re-infection with omicron.

A small study from Denmark that has not yet been peer-reviewed found that in unvaccinated subjects, re-infection with omicron BA.2 was possible after initial infection with omicron BA.1. Despite this finding, the study also concluded that rates of reinfection were low and therefore rare.

As winter approaches and case numbers increase, we are also seeing the emergence of new sub-variables such as BA.4 and BA.5. Early evidence suggests that these novel subvariants are better at escaping immunological memory than omicron BA.1.

What about the risk?

For those who become re-infected, the severity of the disease appears to be milder and is less likely to lead to hospitalization. This is likely because the immune memory can recognize at least part of the re-infected virus.

However, it is difficult to measure disease severity at the population level. A systematic review of case studies found that while some second infections were milder, this was not the case in all cases. Some cases of re-infection led to worse outcomes, including death. (During this study period, one of the original strains, B.1, caused the most primary infections, with re-infections due to alpha or beta variants.)

But while omicron appears to cause more re-infection than other variables, there is not enough robust data to draw firm conclusions about re-infection severity using omicron or other variables.

What we do know for sure is that we need more data from more people to say re-infection is less severe.

We also know from many studies that vaccination provides protection against reinfection, including in previously infected people who then receive subsequent vaccinations.

Another reason to get a boost

A recent study that has not yet been peer-reviewed found that immunity to the omicron BA.1 variant decreases about 7.5-fold with the new omicron BA.4 and BA.5 variants. This means that the antibodies they produce from BA.1 infection, which are able to detect and neutralize 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 in addition to natural exposure to omicron BA.1 gave five times the protection of omicron BA.4 and BA.5 immunity than natural exposure to BA.1 alone.

The data also shows that the strongest protective immunity comes from a combination of triple vaccination and natural infection.

Another study found that this type of hybrid immunity better protects against both reinfection and hospitalization than natural immunity alone, highlighting the importance of vaccination and vaccine boosters.

So the question remains: If our immune memory lasted a year, but was too specific to recognize new variants, would we need a new vaccine every year? Time will tell.


Previous SARS-CoV-2 infection has less protection against the Omicron variant


Introduction of the conversation

This article has been republished from The Conversation under a Creative Commons license. Read the original article.Conversation

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2022-05-17 14:47:32

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