Getting vaccinated is still the smartest thing
CIDRAP News talked with Center for Infectious Disease
Research and Policy (CIDRAP) Director Michael Osterholm, PhD, MPH, to
understand what defines a pandemic, if we’re still in one, and what gives a
pathogen pandemic potential.
CIDRAP News: What exactly is a pandemic?
Michael Osterholm: There’s no magic answer to
that question. From my perspective, I usually say the only examples we
have in modern history are viral infections that are transmitted via the
respiratory route, like the flu and COVID, because the dynamics of transmission
make it a worldwide threat, and “worldwide threat” is important in defining a
pandemic. A pandemic is not just something that happens in one localized area.
Plagues weren’t viruses, but, in the modern world, a
pandemic is almost always a viral infection.
Michael Osterholm: Antibiotics could be an
important part of why bacterial viruses aren't as big of a threat today. But
what’s really at the heart of it is what flu and COVID represent today in terms
of risk—that is, slight changes in the virus result in increased susceptibility.
And when there's a major change in the virus, you virtually have no protection.
“A pandemic is almost always a viral infection.”
For a good example, look at influenza. Each flu pandemic was
caused when there was a major shift in the genetics of the virus, so virtually
no one was immune. If you look at COVID, it was very much the same thing.
CIDRAP News: Why were SARS (severe acute respiratory
syndrome) and MERS (Middle East respiratory syndrome) not pandemics?
Michael Osterholm: Because they are not readily
transmitted. We were able to bring them under control, basically with standard
control measures that you would use for respiratory illness. And that's good
news because the case-fatality rate for SARS and MERS is between 15% and 35%.
For COVID, the case-fatality rate was 1% to 1.5%.
CIDRAP News: So pandemics have less to do with
severity and more to do with how transmissible a virus is?
Michael Osterholm: Both how transmissible it
is and risk are important. For example, if you have a common
cold virus for which we have no previous immunity suddenly spread around the
world, most of us would not consider that a pandemic in the sense that it's not
a severe illness. So there’s an implied status of severe illness.
CIDRAP News: What’s the difference
between a pandemic and an epidemic?
Michael Osterholm: Epidemic relates back to the
issue of transmission. For example, we have a major epidemic of Ebola going on
right now, which surely has a high case-fatality rate. It's a very serious
illness, but it's not readily transmitted via the respiratory route.
CIDRAP News: When does a pandemic start and end?
Michael Osterholm: The start of a pandemic is
much easier to declare because it’s like a suddenly emerging out-of-control
forest fire.
When you get to the point where you have these isolated
fires all over the place, but they're not really burning too much, you can say
that's when the pandemic is over. And that's a much harder one to call.
CIDRAP News: Is the COVID pandemic still going on?
Michael Osterholm: No, I think we can safely say
that we are now adjusting into a more routine cycle of infection. And you can
argue that in several ways. First of all, there's a much greater stability to
the virus that we see now with so much background immunity in the population.
It’s similar to previous influenza pandemics, which were the
hallmark pandemics we had prior to COVID. Clearly, they were situations where
once a large portion of the population either got infected and died or got
infected and recovered, there was a level of protection that, over time,
basically won out over the virus itself.
‘Worldwide threat’ is important in defining a pandemic. A
pandemic is not just something that happens in one localized area.
That's why you still see the virus circulating, but in a way
that, genetically, our body's immune systems are largely able to take on. So
again, if you look at the flu pandemics of the past, in every instance they
just kind of faded away over time and became a background endemic disease.
And today we are in a much more steady-state existence with
COVID because of our preexisting immunity and the relative lack of genetic
change to the virus. We haven't watched it go from the ancestral strain to
Alpha, Beta, Delta, Gamma, or Omicron, like we did in those first four years.
CIDRAP News: I’m thinking about some of the notable
pandemics that preceded the COVID pandemic. Is the AIDS pandemic still going
on?
Michael Osterholm: AIDS is an unusual one in
that it has its foot in both the pandemic and non-pandemic camps—and what I
mean by that is that not everyone was at risk for HIV. If you didn’t have a sex
partner who was infected, you did not have blood exposure, then you weren't at
risk for this.
So if 80% of the world is immune to it or not likely to be
exposed, is that going to be a pandemic? But it still is widespread within each
geographic region of the world, so it gets a little cloudier there.
So there are those who say HIV is not a pandemic, and those
who say it is, or it was, a pandemic, and I agree with those who say it is. But
you could claim either one.
CIDRAP News: What gives a pathogen pandemic potential,
and what future pandemics are experts most worried about?
Michael Osterholm: A virus with respiratory
transmission potential for which, upon a genetic change, could mean many, if
not almost all, the population is susceptible. That's why I coined the term
“angel” or “virus with wings,” because basically the virus has to be in that
mode to rise to the level of a pandemic.
Many other diseases surely can be a problem, but only that
defines dynamic transmission in the community.
Also, it's got to be a disease that is sustainable around
the world. Take cholera, for example. In some places, cholera can be a very
serious epidemic. But it's not going to ever be a problem in Minneapolis-St.
Paul [Minnesota].
CIDRAP News: What public health or preparedness
lessons can we take away from the COVID pandemic?
Michael Osterholm: How poorly prepared we are
for a future pandemic. There was no official review following up after COVID,
so I feel like we've learned very little from the pandemic. And we're hurting
badly in terms of vaccine protection and preparedness.
And the one advance we have is mRNA technology, yet we see a large segment of the population refuses to accept that vaccine.
