It’s been three years since the World Health Organization declared an end to the COVID-19 public health emergency, but COVID still circulates worldwide. Does that mean the pandemic is still going on, just in a non-emergency phase? Or has COVID become an endemic virus, like the flu?
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.
CIDRAP News: Why?
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.