The many definitions of a "pandemic"
The many definitions of a "pandemic"
Or what it would take for the COVID pandemic to officially end
Googling for “the pandemic is not over” yields hundreds of thousands of results that generally fall into two camps:
The pandemic is not over until the WHO or CDC says otherwise
It’s not over because the virus is still spreading around, regardless of official definitions
No one except China is seriously working towards “zero COVID”, so the second definition will likely stay true forever - or at least until we discover some hyper-effective vaccine. But the first definition will likely go away eventually as government authorities declare the COVID pandemic to be over. The question is, what would it take for them to do so?
Official definitions
The Oxford dictionary defines a “pandemic” as:
a disease that spreads over a whole country or the whole world
This is a pretty robust definition with just one caveat: since the common cold and the flu are spread over the whole world, are we living in a “common cold pandemic”? The WHO (surprisingly) doesn’t have a clear definition of a “pandemic” on their website, however a paper published in their official bulletin in 2011 gives the following definition:
A pandemic is defined as “an epidemic occurring worldwide, or over a very wide area, crossing international boundaries and usually affecting a large number of people”. The classical definition includes nothing about population immunity, virology or disease severity. By this definition, pandemics can be said to occur annually in each of the temperate southern and northern hemispheres, given that seasonal epidemics cross international boundaries and affect a large number of people. However, seasonal epidemics are not considered pandemics.
This gives a reason for why common colds and flus are not a “pandemic” - they’re instead a “seasonal epidemic”. The fact that they have a lower mortality (at least for the unvaccinated) is not supposed to be a part of the calculus. The article goes on to explain why the H1N1 variant of the flu was declared a pandemic:
A true influenza pandemic occurs when almost simultaneous transmission takes place worldwide. In the case of pandemic influenza A(H1N1), widespread transmission was documented in both hemispheres between April and September 2009. Transmission occurred early in the influenza season in the temperate southern hemisphere but out of season in the northern hemisphere. This out-of-season transmission is what characterizes an influenza pandemic, as distinct from a pandemic due to another type of virus.
This gives us a total of three criteria of a “seasonal epidemic” and therefore “not a pandemic”:
The disease must be spread across a large number countries
The virus must have clearly defined seasons for the northern and southern hemispheres (things get more complicated around the equator)
There shouldn’t be major outbreaks “out of season”
This does answer the question of “why aren’t common colds a pandemic” but what about diseases like herpes or HPV? They’ve spread to every continent and infect millions of people every year. They’re not particularly severe but severity isn’t supposed to be a part of the pandemic definition. This brings us to the final part of the paper:
In 2009 WHO declared a pandemic several weeks after the criteria for the definition of a classical pandemic had been met. Part of the delay was no doubt related to the nexus between the formal declaration of a pandemic and the manufacture of a pandemic-specific vaccine. If a classical pandemic definition had been used, linking the declaration to vaccine production would have been unnecessary. This could have been done with a severity index and, depending on the availability and quality of the emerging evidence on severity, a pandemic specific vaccine may have been deemed unnecessary. Alternatively authorities may have decided to order vaccine in much smaller quantities.
So in practice there’s a 4th criteria for declaring something to be a “pandemic”: the WHO believes that coordinated action is required to tackle the disease. In the case of H1N1, the primary “coordinated” action was to develop a vaccine and “attempt to make sure that a substantial amount of vaccine was available for the benefit of developing countries”.
This “hidden” criteria was called out in the paper The elusive definition of pandemic influenza, which showcased how back in 2003 the WHO had the following definition on their website:
An influenza pandemic occurs when a new influenza virus appears against which the human population has no immunity, resulting in several, simultaneous epidemics worldwide with enormous numbers of deaths and illness.
However some time in May 2009 they’ve changed their website to remove the references to deaths/illness:
An influenza pandemic may occur when a new influenza virus appears against which the human population has no immunity.
Interestingly this sudden change of definitions caused backlash from the Council of Europe back in 2010, as the H1N1 vaccine was considered a waste of money by many politicians at the time. I surmise that this also explains why the WHO no longer has an official definition of a “pandemic” on their website - it’s easier to just remove it altogether than retroactively litigate whether or not the original definition was fulfilled.
What pandemics are currently active?
As far as I can tell, the only pandemic that’s actually active right now according to the WHO is COVID. Other candidates include:
HIV/AIDS. Wiki calls it a “pandemic” however the WHO never declared it as such and their website refers to the virus as an “epidemic”. The CDC concurs and likewise calls HIV an epidemic.
Monkeypox. The WHO declared it a “Public Health Emergency of International Concern” but doesn’t refer to the virus as a “pandemic” just yet.
Polio. Likewise a “health emergency” since 2014 but there hasn’t been a pandemic declaration.
The CDC also lists the following outbreaks on it’s “Past pandemics” page:
H1N1, declared as such in June 2009. The WHO then declared the pandemic to be over in August 2010.
Hong Kong flu or the 1968 flu. No official declaration issued back then, as far as I can tell.
1957-1958 flu pandemic. Likewise no official declaration, though I did find a WHO report from 1957 stating that the virus had spread to all populated parts of the world aside from "a few islands or territories having no contact with the outside world".
1918 flu pandemic. The WHO didn’t even exist back then, so likewise no official declaration.
Who will decide that the pandemic is over?
The only example of a pandemic actually being declared to be “over” is H1N1, so we can look at their press release from 2010:
“We are now moving into the post-pandemic period. The new H1N1 virus has largely run its course,” Margaret Chan, Director-General of the World Health Organization (WHO), told reporters. The announcement follows an assessment by its International Health Regulations Emergency Committee, which met earlier today, as well as reports from several countries that are now experiencing influenza.
So it sounds like the decision rests with the “Emergency Committee”. Each disease has a separate one - the COVID-19 IHR Committee operated since January 23rd 2020, while the Monkeypox IHR Committee operated since June 23rd 2022. Interestingly the Monkeypox committee was overruled by the head of the WHO in order to declare monkeypox a “public health emergency”.
So what does the COVID committee say about ending the pandemic? Their report in July 2022 had the following statement:
The Committee recognized an overall decoupling of incident cases from severe disease, deaths, and pressure on health systems in the context of increased population immunity. However, the Committee unanimously agreed that the COVID-19 pandemic still meets the criteria of an extraordinary event that continues to adversely impact the health of the world’s population, and that the emergence and international spread of new SARS-CoV-2 variants may present an even greater health impact.
The following reasons are then listed for why COVID is still an emergency:
“Recent increase in the growth rate of cases in many States Parties in different WHO regions”. My reading of this is that the growth rate doesn’t yet follow a seasonal pattern accurately, as places like Mexico had a pretty big wave despite being located in the Northern Hemisphere.
“The continuing and substantial evolution of SARS-CoV-2 virus, which, while inherent to all viruses, is expected to continue in an unpredictable manner”. Presumably they want to see if Omicron is the last major variant.
“Public health and health planning tools to reduce transmission and disease burden (including hospitalisations and admissions to intensive care units of severe cases, and the impact of post COVID-19 condition) are not being implemented in proportion to local transmission levels or health system capacities”. Presumably this refers to some healthcare systems still struggling to cope with COVID cases, though this was also the case with flu waves in the past.
“There are inadequacies in risk communication and community engagement related to the need for the implementation or adjustment of PHSM, as well as a disconnect in the perception of risk posed by COVID-19 between scientific communities, political leaders and the general public”. Presumably the WHO wants people to at least somewhat acknowledge that the virus still exists and keeping up the official emergency is the most powerful tool at their disposal.
So when could the pandemic be officially over? Presumably the earliest possible date would be August 2023, assuming that:
Southern hemisphere countries don’t experience another major wave until their next winter (June-August 2023)
Northern countries see a major COVID wave this winter, but not the following summer
The WHO no longer feels like “continued coordination” is necessary. This is the vaguest criteria but presumably it should be met once COVID’s seasonality is fully established.
The WHO director doesn’t override the emergency committee, as seen with the Monkeypox emergency declaration.
Until then people will still be technically correct whenever they say that “the pandemic is not over”.