Australia is having a major challenge with the Delta variant of concern right now. And it’s understandable some people are feeling uncertain about getting a COVID-19 vaccine when available.
Dr. S.S. Vasan,
COVID-19 project leader at CSIRO, answers some common questions about the Delta
variant and vaccine effectiveness. Last year, Dr. Vasan led the preclinical
trials of the Oxford-AstraZeneca vaccine at our Australian Centre for Disease
Preparedness (ACDP) in Geelong. Since the beginning of the pandemic, Vasan has
been closely monitoring new variants of concern of SARS-CoV-2 (the virus that
causes COVID-19) and researching whether vaccines will work against them. In
conversation with Dr. Vasan.
■ What is a
SARS-CoV-2 variant?
Simply put, when the virus changes from its original genetic
makeup, we call it a variant.
To detect variants, we compare the virus genomes against the
original or reference isolate called ‘Wuhan-Hu-1’ and see what’s changed.
Even a single mutation technically makes it a ‘variant’.
Viruses like SARS-CoV-2 need to make copies of themselves in order to survive.
When they make those copies, sometimes the copies might have errors. Imagine
using a photocopier to make a copy of a copy of a copy and so on. Eventually,
some letters might look a little different where the ink has smudged, or part of
the copy is missing, or new letters have even been added in somehow.
Because mutations are especially frequent for RNA viruses
like SARS-CoV-2, we’re looking at tens of thousands of variants. But most of
them are not concerning—only a handful are currently of interest or concern
(more on this below).
■ How much more
contagious is Delta than previous SARS-CoV-2 variants?
The Delta variant of concern is the most important to date.
According to the World Health Organization (WHO), there is
increasing evidence of greater transmissibility and secondary attack rate
(disease spreading to those close to the person who’s infected).
The Delta variant has spread to at least 135 countries,
including Australia.
■ And what is Delta
Plus?
Some Delta isolates have a mutation called K417N, which is
also present in the Beta and Gamma variants of concern. Some media outlets have
dubbed this ‘Delta Plus’. Scientists are studying this mutation’s impact on
vaccines and antibody therapies.
■ Is Delta more
deadly?
The WHO says this variant of concern has an increased risk
of hospitalization. This is unsurprising because increased transmissibility
could go hand-in-hand with case severity until most of the world’s population
is vaccinated.
A study from February to June in Canada, yet to be
peer-reviewed, compared non-variants of concern with Delta. It found people
infected with the Delta variant were:
§
105% more likely to be hospitalized
§
241% more likely to be admitted to an intensive
care unit
§
121% more likely to die from the disease.
For the other three variants of concern, these values were
52%, 89% and 51% respectively. This shows the Delta is the most problematic
variant of concern to date.
■ Does Delta affect
younger people more?
We’re starting to see this, but comprehensive evidence will
take time.
One of the largest studies of its kind in India, yet to be
peer-reviewed, showed that mortality increased by almost 40% in the second
wave. This was particularly in the younger patients of age less than 45 years.
It’s especially sad to see media reports of younger people
in Australia dying of COVID-19. This is why vaccinations are so important to
protect our entire population.
■ Are the Pfizer and
AstraZeneca vaccines effective against the Delta variant?
Yes, both vaccines are effective against the Delta variant.
A peer-reviewed study in The New England Journal of Medicine showed that after
two doses:
A pfizer-BioNTech vaccine is 85.3 to 90.1% effective against
symptomatic disease caused by Delta
Oxford-AstraZeneca vaccine is 61.3 to 71.8% effective
against symptomatic disease caused by Delta
If you get infected after you’re vaccinated, it is likely to
be mild rather than severe disease. Therefore, vaccination is absolutely worth
it – both to protect yourself and to reduce transmission to our family and
community.
■ If you’re
waiting for your second dose, will your first vaccine provide any protection
against Delta?
Absolutely! The New England Journal of Medicine paper
reported 25.2 to 35.7% effectiveness after one dose of either vaccine against
the Delta variant.
So even one dose of Pfizer or AstraZeneca will give you some
protection against Delta. And set you on the path to getting even better
protection from your second dose.
■ Do variants
happen in populations where the disease is spreading fast?
The more a virus is able to replicate and spread in a
population, the greater the likelihood of mutations of consequence. Where the
environment permits highly transmissible variants, we also expect disease
severity to go up.
But if we halt transmission, we can suppress the spread of
variants. This is why vaccinations and lockdowns are an essential part of pandemic response. They drive transmission down and drive the virus evolution
towards less severe disease outcomes.
“We don’t yet have a SARS-CoV-2 variant of high consequence
that significantly reduces the effectiveness of prevention or medical
countermeasures. Hopefully, most people will be vaccinated before we face that
situation. Getting a COVID-19 vaccine is one of the best protections we
currently have”
■ What is a ‘variant of concern’ and a ‘variant of
interest’?
National ‘concern about a variant’ of SARS-CoV-2 is often
justified. But that doesn’t necessarily make it a ‘variant of concern’ to the
WHO and the rest of the world.
The definitions we use in Australia are consistent with the
US Centers for Disease Control (CDC) and the WHO.
§
Definition of ‘variant of interest’ (sometimes
called a ‘variant under investigation)
§
Changes to receptor binding (the way the virus
attaches to cells)
§
Reduced antibody neutralization
§
Reduced efficacy of treatments
§
Potential diagnostic impact
§ A predicted increase in transmissibility or
disease severity.
§
These four variants—Eta, Iota, Kappa, Lambda—are
of interest. This is one step below concern.
§
A ‘variant of concern’ has a greater impact
across all these measures:
§
Changes to receptor binding, often targeted by
vaccines
§
Significantly reduced antibody neutralization
§
Reduced vaccine or treatment effectiveness
§
Diagnostic detection failures
§
Evidence of increased transmissibility and more
severe disease (in terms of hospitalizations or deaths).
Out of tens of thousands of variants, only four are
currently of concern to the WHO: Alpha, Beta, Gamma, and Delta.
There is one step higher than a variant of concern—called a
‘variant of high consequence’. Thankfully, we don’t yet have one for
SARS-CoV-2.
■ Will we need
booster shots to keep up with the variants? If so, how soon?
Research is ongoing on this topic, called ‘vaccine
matching’. If we take both doses of either vaccine, we should be okay for at
least a year, based on neutralization efficacy studies to date.
New guidelines will emerge based on how the virus evolves,
and how the vaccines are performing.
■ What about other
variants of concern—do
the vaccines work against those too?
Some variants like the D614G (dubbed the G-strain) attract a
lot of media attention. But they don’t necessarily affect vaccines, as my team
was the first to demonstrate last year.
Others like Beta affect many first-generation vaccines.
There are also newer vaccines, such as the Indian Institute of Science’s warm
vaccine Mynvax, which withstood all four variants of concern in our laboratory
tests.
So we do have positive news. We don’t yet have a SARS-CoV-2 a variant of high consequence that significantly reduces the effectiveness of
prevention or medical countermeasures.
Hopefully, most people will be vaccinated before we face that
situation. Getting a COVID-19 vaccine is one of the best protections we
currently have.
But you’ll be safe knowing the vaccines available in
Australia are effective at protecting against severe disease from the Delta
variant.
No comments:
Post a Comment