Before March 2020, many people saw pandemics
as a thing of the past. Then came COVID-19. Scientists still do not know
exactly where the virus that caused it — SARS-CoV-2 — came from, but it soon
reached almost every country worldwide. Over 2 years, the virus has evolved,
producing several variants. In this Special Feature, we look at the evolution
of SARS-CoV-2 and ask what lessons scientists have learned.
Share on PinterestWhat have we learned in 2 years of COVID-19? Image credit: Dia Dipasupil/Getty Images.
In late 2019, there was a sudden increaseTrusted Source in pneumonia cases in central China. By
January 7, scientists had identified and isolated a previously unknown
coronavirus, now designated SARS-CoV-2.
On March 11, 2020, the World Health Organization (WHO)Trusted Source declared COVID-19 a pandemic.
Now, 2 years on, authorities have recorded more than 458 million cases of COVID-19, the disease resulting from
SARS-CoV-2. The disease has also played a role in the deaths of more than 6
million people.
Stay informed with live updates on
the current COVID-19 outbreak and visit our coronavirus hub for more advice on prevention and
treatment.
However, the actual death toll may well be far higher than 6
million. According to a recent paper in The LancetTrusted Source, the actual death toll may be at least three
times that.
On December 29, 2019, experts linkedTrusted Source four cases of pneumonia of unknown etiologyTrusted Source to the Huanan Seafood Wholesale Market
in Wuhan, central China.
On January 7, 2020, researchers isolated the causative agent,
SARS-CoV-2, and on January 10, they sequenced its genome.
By January 2, 2020, doctors had confirmed that 41 peopleTrusted Source in a Wuhan hospital with severe
respiratory illness had a SARS-CoV-2 infection. Of these individuals, 27 had
had exposure to the seafood market.
Many
coronaviruses exist, affecting both animals and people. Most cause infections
with mild to moderate symptoms in the upper respiratory tract, such as colds.
In
recent years, two coronaviruses — SARS-CoV and MERS-CoVTrusted Source — have caused more severe disease. SARS-CoV, which
scientists identified in November 2002, was responsible for severe acute
respiratory syndrome (SARS), which emerged in Asia. The Centers for Disease
Control and Prevention (CDC)Trusted Source note
that of the 8,096 people with a known SARS infection, 774 died. There have been
no reported cases since 2004.
Scientists
first identified Middle East Respiratory Syndrome (MERS), the disease that
MERS-CoV-2 causes, in 2012 in Saudi Arabia. The mortality rate for MERS is high
— of every 10 people with the infection, three or fourTrusted Source die.
There continue to be occasional, localized outbreaks of this disease.
Both
of these coronaviruses caused diseases with high fatality rates, but it was
possible to contain the spread before they reached pandemic levels. So, were we
ready for the next coronavirus?
Experts
believe that SARSTrusted Source came from bats and that MERSTrusted Source crossed over to people from camels. However, for
SARS-CoV-2, researchers have not all agreed on any of the many existing
theories.
At
first, people thought that SARS-CoV-2 might have come directly from batsTrusted Source. Scientists discounted that
theory, though, as the spike protein on SARS-CoV-2 is very different from that
on the coronaviruses present in bats.
Now,
researchers think it is likely that the virus originated in bats but had an
intermediate host between bats and people. A recent study — which has not yet undergone peer review — suggests
that live mammals for sale at the Huanan Seafood Wholesale Market in
Wuhan, the epicenter of early cases, might have been the intermediate host.
Another recent study — also yet to undergo peer review — that analyzed the
evolution of SARS-CoV-2 suggests that “SARS-CoV-2 emergence likely resulted
from multiple zoonotic events.” The researchers do not suggest what the
intermediate animal hosts might be.
Alternatively, did SARS-CoV-2 escape from a laboratory in Wuhan,
as some media outletsTrusted Source have suggested? The WHOTrusted Source has dismissed this
theory as “extremely unlikely.”
So,
there is still uncertainty about the origins of SARS-CoV-2. And this may be
due, in some measure, to a lack of international cooperation, as Prof. Jonathan Stoye, a virologist at the Francis Crick Institute in London,
United Kingdom, told Medical
News Today.
In
his opinion, “one mistake was to start pointing fingers at China and blaming
them for the origin of this virus. I think that, naturally, led to pushback
from the Chinese [authorities].”
He
added: “I absolutely believe in natural origins [of SARS-CoV-2], but the
Chinese [authorities] could have made things easier if they’d opened up their
books straightaway. They weren’t going to do that when they were being accused
of being responsible [for the virus].”
For
almost a year, the original Wuhan variant of SARS-CoV-2 moved across the globe.
Then, in late 2020, the number of COVID-19 cases increased rapidly in South
East England, in the United Kingdom.
Researchers
discovered that a new variant, which was 50% more transmissibleTrusted Source than the original and had 17 unique mutationsTrusted Source, was responsible. In December 2020, the WHO designated it
B.1.1.7, or the Alpha variant.
Scientists
have since identified many other variants, but the WHO has only designated five
as variants of concern (VOC)Trusted Source.
The VOCs and the location of their initial identification areTrusted Source:
- Alpha (B.1.1.7): The U.K., September 2020
- Beta (B.1.351): South Africa, October 2020
- Gamma (P.1): Brazil, December 2020
- Delta (B.1.617.2): India, October 2020
- Omicron (B.1.1.529): Multiple countries, November 2021
Each
variant has different features. Some variants are more transmissible than
others, and some are more virulent. It is these features that have caused the
multiple waves of COVID-19.
“The regular and rapid emergence of
new variants in the past 2 years have made the course of the pandemic very
unpredictable.”
– Dr. Arturo Casadevall,
distinguished professor and chair of molecular microbiology and immunology and
infectious diseases at the Johns Hopkins Bloomberg School of Public Health in
Baltimore
Viruses mutateTrusted Source all
the time. Each time they replicate, which they do frequently, their genetic
material is copied. A mutation happens when part of the genetic material is
copied incorrectly.
In
a coronavirus, the genetic material is ribonucleic acid (RNA). An enzyme called
RNA polymerase controls the replication, and it often makes errors. Most
mutations create a virus that cannot replicate and spread among people.
However, some mutations lead to a virus that can replicate: a variant.
A mutation might give the virus a selective advantage, such
as better transmissibility or greater virulence. If it is more transmissible,
the variant may spread faster and outcompete previous variants. This is what
happened with the Alpha, Delta, and Omicron variants of the coronavirus.
Some
situations give viruses more opportunities to mutate, as Dr. Christopher
Coleman, assistant professor of infection
immunology at the University of Nottingham, U.K., explained to MNT:
“Viruses naturally mutate as they replicate, so in an
immunocompromised host where the virus replicates more easily, there will be a
correspondingly increased number of mutations.”
Omicron
has more than 50 mutationsTrusted Source,
of which some 30Trusted Source are
in the spike protein that the virus uses to gain entry to host cells. One theory suggests that it may have evolved in people with HIV, a virus that suppresses the immune system.
Hosts and mutations
Moving between host species also increases the mutation rate.
Dr. Coleman added that the “[i]nfection of animals by humans will mean the
virus then adapts to a new host, which involves mutations.”
Domestic animals, such as cats, dogs, and ferrets, have had
SARS-CoV-2 infections. The CDCTrusted Source notes
that on one mink farm in Michigan, several animals contracted the virus, which
then passed back to workers. On testing, the viral samples from the workers
contained several mink-related mutations.
“You are getting evolution
occurring from different
starting points. Whether they are occurring through immunosuppressed or
immunocompromised patients, or whether they are happening through animals, or
how, I don’t know that we know, and I don’t know that we will ever really
know.”
— Prof. Jonathan Stoye
Vaccines
Decades of research into coronaviruses led to the rapid
development of vaccines, many of them using new technologies. These have
been incredibly effectiveTrusted Source in
reducing the impact of COVID-19 and allowing society to regain some measure of
normality.
But, as Prof. Stoye explained, “[i]n retrospect, we have been
‘lucky’ that it has been possible to make a vaccine against this particular
virus, whereas for things like HIV […], we still don’t have vaccines.”
However, vaccines designed against one variant might be
ineffective against another.
“The evolution of SARS-CoV-2
variants upended many optimistic predictions made when the vaccines were rolled
out in 2020.”
— Dr. Arturo Casadevall
Despite the evolution of variants, vaccines still guard against
severe COVID-19, particularly in those who have received multiple vaccinations.
Despite suggestions that vaccines might even drive the evolution
of new vaccine-resistant variants, this does not seem to be the case, as
a recent report states: “Given the emergence of immunity-evading
variants even before vaccines were broadly deployed, it is hard to implicate
vaccines or vaccine deployment strategies as the major drivers of immune
evasion.”
Prof. Stoye feels that vaccines will continue to be important.
“I suspect we will have to have yearly boosters of the vaccine, at least for
the foreseeable future,” he said.
And he expressed a hope that research might create more powerful
vaccines:
“It would be very nice if
scientists could establish a pan-coronavirus vaccine that worked against
multiple viruses. That has to be one of the hopes of the future — that you will
have a method of vaccination that will protect you against various viruses.”
The end
of the pandemic?
After 2 years, people are becoming tired of restrictions,
feeling that the pandemic should surely be over. However, Prof. Stoye is one of
many experts expressing concern that governments are removing COVID-19 testing
and control measures too early.
“One of the things I’m frightened about is that we will, in
fact, lose our ability to follow these processes as we stop testing and
sequencing so much. […] As we test less, as we sequence less, we will lose that
ability to recognize new variants in real time,” he told us.
Global
lessons for the future
— Prof. Jonathan Stoye
This is not the first pandemic, and it is unlikely to be the
last. Some aspects have been well-handled, while others have not, and the
geopolitical debates will continue for years. At least vaccines are continuing
to protect against severe illness and death from all variants.
Possibly the most important lesson is that it is crucial to
address future disease
outbreaks globally. Although people in high income countries have had
ready access to vaccines and boosters, many African countries have yet to
vaccinate even 10% of their population due to inequitable
vaccine distribution.
The lack of widespread vaccination can also contribute to the
development of new variants.
Prof. Stoye stressed the importance of global cooperation in
countering pandemics:
“The global aspects
of this are the interesting and important ones. Whether those lessons will be
learned, I don’t know. […] I would hate to think that, suppose in 2 or
3 years down the track, we are living comfortably with this virus, and SARS-3
comes along or HIV5, and we have forgotten all the lessons we have learned.
It’s trying to retain that memory that is the important lesson.”
Source : Medical News Today
0 Comments