Thread by @bopinion

In Italy, there’s an ongoing public debate about whether the coronavirus has mutated into a weaker form.

How optimistic should we allow ourselves to feel? trib.al/BgFutgX

A leading virologist and doctor, Arnaldo Caruso, endorsed this idea as these measures continue to decline or hold steady as Italy reopens:

➡️Deaths
➡️Cases
➡️Severely ill patients
➡️Viral load on swabs

He suggested it could vanish even without a vaccine trib.al/BgFutgX

Viruses mutate over time, sometimes significantly. These shifts are why we need new flu vaccines every year.

There’s also an evolutionary trade-off between deadliness and transmission -- a virus that kills too many can’t spread, so some become milder trib.al/BgFutgX

Scientists working on vaccines speed up the mutation process to produce "live attenuated virus" vaccines, which produce immunity but not a severe illness.

The question is whether the Covid-19 virus, known as SARS-CoV2, might take this journey on its own trib.al/BgFutgX

Coronaviruses are slow to mutate compared to influenza, and Covid-19 doesn’t appear to be different.

Most mutations don’t result in any kind of meaningful change to how a virus acts trib.al/BgFutgX

One study looking at over 15,000 genomes examined the emergence of a more transmissible strain.

Any mutations appeared to be neutral or slightly harmful to the virus’s spread. Most other genetic changes seen didn’t seem like evolutionary adaptations trib.al/BgFutgX

Even for a pandemic flu -- a virus much more given to rapid change than a coronavirus -- a few months would be a short timeline for a widespread functional mutation trib.al/BgFutgX

There’s no clear cut evolutionary case for a virus like SARS-CoV2, which has already managed to infect more than 6 million people and often causes mild symptoms, to quickly get milder.

If anything, it seems more likely to be genetically stable trib.al/BgFutgX

Without a lot more data and information, the evidence that mutation fans are providing remains anecdotal and may be compromised by selection bias.

Less viral activity in lab experiments is more compelling, but Caruso describes it as a very early result trib.al/BgFutgX

If the virus isn’t mutating into a milder form, what else can explain why it doesn’t seem as bad? Many other things, including:

🔬Expanded testing and surveillance are catching people earlier
😷Public health measures are working
🌞Seasonal effects trib.al/BgFutgX

The most prudent path for a long time to come seems to be to treat Covid-19 as the deadly threat it was in Italy a short few weeks ago and continues to be around the world trib.al/BgFutgX