EXPLAINER: What is the Mu variant? What will endemic COVID-19 be like?

There has been a slow burn of media coverage regarding another SARS-CoV-2 variant of interest called Mu. While it’s still too soon to tell how it will affect the current pandemic (if at all), the best way to avoid any unnecessary panic or mischaracterization is to address the topic directly. Dr Vinod Balasubramaniam is a virologist at the Jeffrey Cheah School of Medicine & Health Sciences at Monash University Malaysia.

How dangerous is this new variant? Can it escape vaccines?

This new Mu variant is listed as Variant of Interest (VOI). Like VOCs (Variants of Concern), VOIs may be more contagious, better able to evade the immune system, more resistant to available treatments, or harder to detect.

There is less research on their impact on infections and hospitalisations compared to VOCs. Additionally, they can cause outbreaks in multiple countries, but are not as widespread as VOCs. VOIs are ‘of interest’ to certain countries based on infection rates, which is why some VOIs are listed on the CDC’s website but not the WHO’s, and vice versa.

Why is this particular variant a specific concern?

All viruses, including SARS-CoV-2 that causes COVID-19, mutate over time and most mutations have little or no effect on the properties of the virus. But certain mutations can impact the properties of a virus and influence how easily it spreads, the severity of the disease it causes, and its resistance to vaccines, drugs and other countermeasures.

Mu, or B.1.621 variant, has a number of mutations that suggest it could be more resistant to vaccines. The new variant detected in 39 countries was found to possess a ‘constellation of mutations that indicate potential properties of immune escape’. Mu is the fifth ‘variant of interest’ to be monitored by the World Health Organization (WHO) since March this year.

Mu has a mutation called P681H, first reported in the Alpha variant, that is potentially responsible for faster transmission. However, this study is still in preprint, meaning its findings have yet to be formally reviewed by other scientists. We can’t be sure of P681H’s effects on the virus’s behaviour just yet.

Mu also has the mutations E484K and K417N, which are associated with being able to evade antibodies against the coronavirus, and the evidence on this is more concrete. These mutations also occur in the Beta variant, and so it’s possible that Mu might behave like Beta, which some vaccines are less effective against.

Mu also has other mutations, including R346K and Y144T, whose consequences are unknown, hence the need for further analysis. But can Mu actually evade pre-existing immunity? As yet there’s only limited information on this, with a study from a lab in Rome showing that the Pfizer/BioNTech vaccine was less effective against Mu compared to other variants when tested in a lab-based experiment.

Despite this, the study still considered the protection offered against Mu by the vaccine to be robust. Really, we don’t yet know whether Mu’s mutations will translate into increased infection and disease.

Striking reports on Mu have been appearing, though. In late July, a news station in Florida reported that 10 per cent of samples sequenced at the University of Miami were Mu. In early August, Reuters reported that seven fully vaccinated residents of a nursing home in Belgium had died from an outbreak of Mu.

However, these are limited snapshots of the variant’s behaviour. The global prevalence of the Mu variant among sequenced COVID-19 cases is currently below 0.1 per cent. But it has consistently increased in countries such as Colombia with 39 per cent and Ecuador with a 13 per cent increase.

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How important is vaccination in the fight against new variants?

Every time the virus reproduces inside someone there’s a chance of it mutating and a new variant emerging. This is a numbers game. It’s a random process, a bit like rolling dice. The more you roll, the greater the chance of new variants appearing. It’s basically a ticking timebomb.

The main way to stop variants is global vaccination. The emergence of Mu reminds us of how important that goal remains. We must get vaccines to these people as quickly as possible, both to help the people there who are vulnerable but also to stop new variants from emerging. Otherwise, our exit from the pandemic will be set back, possibly for months on end.

The only way is to sprint towards the finish line to have any protection against these emerging variants. In the case of the Mu variant, as explained before, it contains the recipe for disaster as an initial look at the viral genome suggests the possibility of immune evading capabilities similar to other variants of concern.

As scientists globally are looking in-depth at its pathogenicity, virulence and transmission, we will only get a clearer picture in the coming months. But countries cannot rest on their laurels and risk another variant wreaking havoc similarly to the current situation with the Delta variant. We must stay vigilant and tighten control, testing at our borders, and monitoring this development closely.

Can we live with ‘endemic’ COVID-19?

The Delta variant, first identified in India, is a more transmissible form of the novel coronavirus which has spread to at least 77 countries and regions. Delta has quickly become the dominant variant in the majority of countries worldwide, causing spikes in new and breakthrough infections in vaccinated individuals. There is some indication that the Delta variant may also result in more severe disease. A lockdown without enforced COVID-19-appropriate behaviour will allow the virus to spread. Therefore, adopting COVID-19-appropriate behaviour, including wearing proper face masks, maintaining appropriate distancing, and proper hand hygiene, is pertinent to winning the war against the virus.

There are many examples of improper blanket lockdowns (partial closure of the economic sector without adopting COVID-19-appropriate behaviour) which have resulted in an increase of cases, especially in Malaysia and India.

And lockdowns have already caused severe repercussions in terms of Australia’s economic stability.

At the same time, governments can’t simply let the floodgates open and allow 100 per cent of economic sectors to be fully open, which spells disaster. We can’t afford to overload our already critical healthcare system.

The government should tread carefully, putting in restrictions that let only fully vaccinated individuals enjoy these economic privileges, while stricter enforcement should be placed to restrict non-vaccinated individuals from being exposed to large masses of people. We must remember this IS THE PANDEMIC OF THE UNVACCINATED!

The government should increase efforts to vaccinate those who are eligible even if it means using legal avenues for those who still resist vaccination while preparing plans for booster doses. We will need booster doses at some point since more emerging variants are circulating. As explained above, the government should not delay in making decisions on the booster dose. IT IS ABSOLUTELY PERTINENT.

We must first understand that the vaccines we have currently are not a miracle cure. They were designed to provide immunity against symptoms/disease caused by the virus and the possibility of reducing transmission of the virus from person to person.

Can we eradicate the virus? Can we achieve herd immunity? Herd immunity occurs when a large portion of a community (the herd) becomes immune to a disease, making the spread of disease from person to person unlikely. The virus needs susceptible hosts (humans/animals) to thrive. The vaccine stops this. But is herd immunity still possible? What are the challenges?

  • It’s unclear whether vaccines prevent transmission with new variants. There is still inconclusive real-world data to show that current vaccines used are able to fully stop transmission of the Delta strain/any new emerging strain which is predominant. Apart from that, with the virus now causing sporadic infection in the community both in vaccinated (health care workers) and unvaccinated individuals, it is even harder for us to track and trace the infections.
  • New variants change the herd-immunity equation with the Delta strain able to infect vaccinated individuals.
  • Vaccines might change human behaviours. The problem is that, as more people are vaccinated, there is a possibility that they will increase their interactions without proper standard operating procedures, and that changes the herd-immunity equation, which relies in part on how many people are being exposed to the virus.
  • We’re still lacking conclusive data on waning immunity with the possibility of booster doses on the horizon to better protect against the Delta strain. With these logistics, procurement will come into play again, and how long will that take?

It is possible, experts say, that COVID-19 could become a seasonal illness, like the flu. Virologists call this an ‘endemic’ disease — one that is constantly circulating among us. In the years and decades to come, many people will be exposed to it in childhood and develop some immunity, which would protect them later in life against serious disease.

However, given how the pandemic has been handled so far, it is likely that it will become endemic, with the virus probably taking a similar route to the four existing ‘human’ coronaviruses that are already in circulation and cause upper respiratory infections.

Having had COVID-19 is unlikely to give you lifelong immunity. But, even if you are infected again, the second infection will likely be less serious. We might need booster doses against variants and to provide optimal immunological memory against the disease. If SARS-CoV-2 experiences antigenic evolution at rates that are similar to influenza, annual shots for vulnerable populations may well be necessary.”


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