The starting list.
We start with a list of all 77 candidate pathogens based on various watch lists
and other prioritizations that have been circulated.
Is the pathogen endemic to the United States?
We then divide those pathogens into those for which there is ongoing local
incidence (i.e., are endemic to the United States) and those that are not
currently circulating in the United States.
Filtering the endemic pathogens.
Let’s first consider the endemic group.
Are World Cup activities likely to increase transmission?
These can be divided into pathogens where there is evidence to support likely
increased transmission at World Cup related activities, and pathogens for
which there is not evidence to support such an increase.
Understanding increased World Cup transmission →
Pathogens with no increased transmission risk.
If a pathogen is endemic to the United States and there will not be elevated
transmission at World Cup related events, then the tournament only increases
risk if there are significant additional importations. We presume that if
importations increase pathogen prevalence by 5% or less, then that pathogen is
not of elevated concern and should be excluded from the priority pathogen
list.
Significant importation filter.
Most pathogens in this category are excluded by this criterion. The
exception is Hepatitis B, which has much higher prevalence elsewhere in
the world than in the United States.
Pathogens with increased transmission at the World Cup.
Now let’s continue to evaluate Hepatitis B along with the group of pathogens for which we have evidence to
support increased transmission at World Cup related events.
Transmission seeded from local and imported cases.
To evaluate these pathogens we first consider the number of cases among
international travelers coming to the World Cup, and local cases who are
attending World Cup events.
Onward transmission from local and imported cases.
Both imported and local cases may seed outbreaks at World Cup events. We run
simple simulations of onward transmission over the period of World Cup
activities in a host city (assumed to be 17 days based on the host cities with
the most games happening at a tight time frame). This gives us an estimate of
the total number of cases of a pathogen that will occur at events associated
with the World Cup.
Identifying the Excess
Of course, the local index cases and some number of onward transmissions from
those cases would have occurred anyway even if the World Cup had not occurred.
We perform simulations of outbreaks with transmission rates expected in the
general community to determine how many of these “local” outbreak cases would
have occurred anyway.
The impact of the World Cup
Total impact of infectious diseases at the World Cup is based on this number
of excess cases and a disease-specific per-case impact (comprehensive of all
health and financial costs). If this expected impact is above some threshold
(here $25,000), the disease is included in the priority pathogen list.
Otherwise it is excluded.
Pathogens included due to importation and elevated transmission.
Combining the importation filter with the impact assessment, we have
determined that COVID-19, hepatitis B, measles, norovirus, RSV, seasonal
influenza, and tuberculosis should be included in the priority pathogen
list.
Non-endemic pathogens
We now return our attention to pathogens that are not at this point endemic to
the United States.
Are the conditions for endemic transmission present?
This group can be divided based on whether we think conditions might be
present that would allow that pathogen to establish endemic transmission.
Because the costs of endemic transmission are so high over time, all pathogens
that might be capable of establishing endemic transmission are considered to
be priority pathogens.
Note that the endemic risk from arboviruses and malaria are limited to certain parts of the country.
Where arbovirus & malaria risk is concentrated →
Risk from other non-endemic pathogens.
The remaining non-endemic pathogens can be evaluated based on their
importation and outbreak risks. This calculation is the similar to what we did
for endemic pathogens with elevated transmission during World Cup event,
except that there is no need to account for baseline transmission from local
sources.
It is worth remembering that we are only focused on increase risk from the World Cup,
not risk overall; hence, these results do not reflect the absolute risk posed by
these pathogens.
Assessment of other non-endemic pathogens.
Based on the expected number of importations and outbreak impact, we exclude
an additional 18 pathogens and elevate
2 (Lassa fever and Andes lineage hantavirus) to the
priority list because their expected outbreak impact exceeds the threshold.
Summary
Based on the screening protocol at this point, our priority pathogen list
includes 14 pathogens. The
remaining 63 pathogens have been excluded by the process.
Priority pathogen groups.
Seasonal respiratory viruses may be imported from areas of the world in the midst of
their respiratory virus season, and circulate easily in crowded conditions.
Mosquito borne pathogens include pathogens with a competent vector and confirmed transmission in the continental United States. These are only of risk in southern host cities.
High importation risk are pathogens causing chronic infections that are far more common elsewhere in the world.
Locally present pathogens with excess transmission are included due to increased outbreak risk.
Critical scenarios encompass hypothetical scenarios of note, and Lassa fever, which is rare, but common compared to other hemorrhagic fevers.
Acknowledgements
This screening assessment represents the tireless work of a team of students,
postdocs and faculty in the Atlantic Coast Center for the Infectious Disease
Dynamics and Analytics (ACCIDDA), and collaborators from throughout Insight
Net.
WC 2026 Threat Assessment