Not all outbreaks deserve the same level of attention. A seasonal Lassa fever cluster in West Africa and a novel respiratory virus spreading across three continents are fundamentally different threats, but a headline about either one can trigger the same anxiety. Severity scoring exists to replace that anxiety with a number you can act on.

PandemicAlarm assigns every outbreak event a score from 1 to 5 based on measurable factors: pathogen lethality, transmission dynamics, geographic spread, healthcare capacity in affected regions, and the availability of countermeasures like vaccines or treatments. That score tells you, in seconds, whether an event needs your attention or just your awareness.

Key Takeaways

What does severity 1-5 actually mean?

Each severity level corresponds to a distinct combination of pathogen danger, transmission potential, and geographic scope that determines how much attention and action you should give an outbreak event. Level 1 means the event is expected and contained; Level 5 means the event has global reach and demands immediate behavioral changes from individuals, not just governments.

Level 1: Routine. Expected outbreaks in expected places. Seasonal Lassa fever in Nigeria fits here. Nigeria reports 500-1,000 confirmed Lassa cases annually, with spikes during the dry season from January through April. The virus circulates in Mastomys rats, and human cases cluster in rural farming communities. If you're not in the affected region, Level 1 events require zero action. Even within the region, established surveillance and treatment protocols exist.

Other Level 1 examples: seasonal influenza outbreaks, endemic dengue during rainy season in Southeast Asia, and periodic cholera cases in areas with known contamination risks.

Level 2: Elevated. Something is slightly off. Case counts exceed seasonal norms, or a known pathogen appears in an unusual location. When avian influenza H5N1 was detected in US dairy cattle herds in early 2024, it initially scored Level 2. The virus wasn't new, but cattle were an unexpected host. Worth watching closely. Not worth losing sleep over.

At Level 2, travelers to affected regions should take precautions. Everyone else should note the event and check back weekly.

Level 3: High. A serious pathogen with confirmed person-to-person transmission, growing case counts, or spread to populations with limited healthcare access. Bangladesh's 2023 dengue surge is an instructive case. Over 321,000 cases and more than 1,700 deaths were reported that year, according to Bangladesh's Directorate General of Health Services. Those numbers shattered previous records. Hospitals in Dhaka ran out of beds. The surge scored Level 3 because, despite the severity within Bangladesh, dengue's transmission mechanics (mosquito-borne, no efficient person-to-person spread) limited the risk of rapid international expansion.

Rwanda's September 2024 Marburg outbreak also started at Level 3. Marburg carries a case fatality rate above 60% historically, and healthcare worker infections suggested nosocomial spread. Rapid containment by Rwandan authorities prevented it from climbing higher.

Level 4: Severe. Sustained cross-border transmission with community spread in multiple countries. WHO has likely declared or is actively considering a PHEIC (Public Health Emergency of International Concern). At Level 4, the window for cheap, calm preparation is closing. Masks, medications, and shelf-stable supplies are still available at normal prices, but that won't last.

Ebola in West Africa escalated to Level 4 in mid-2014 as it moved through Guinea, Sierra Leone, and Liberia. The 2022 Mpox outbreak reached Level 4 when cases appeared in dozens of non-endemic countries simultaneously.

Level 5: Critical / Pandemic. Global transmission with significant mortality and societal disruption. COVID-19 hit Level 5 in March 2020 when WHO declared a pandemic, with over 118,000 cases across 114 countries at the time of declaration. Mpox Clade Ib currently holds a Level 5 rating from PandemicAlarm due to its novel recombinant strain, high case fatality rate, and sustained cross-border spread in Central and East Africa.

Level 5 events are rare. Since 2000, only a handful of disease events have reached this threshold. When one does, the time for preparation has largely passed. If you've been monitoring at Levels 3 and 4, you're already positioned. If you haven't, you're competing with panicked crowds for dwindling supplies.

Who assigns severity scores and how?

PandemicAlarm's severity scores are generated through a structured assessment that combines quantitative data from official sources with epidemiological judgment based on established frameworks. Scores draw from WHO Disease Outbreak News reports, CDC surveillance data, ProMED alerts, ECDC risk assessments, and peer-reviewed literature on the pathogen in question.

WHO itself uses a qualitative risk assessment scale: low, moderate, high, very high. That assessment feeds into our scoring but doesn't determine it alone. WHO's mandate is to advise governments, not individuals. A WHO risk assessment of "moderate" for a given country might correspond to a PandemicAlarm score of 3 if the affected region has limited healthcare infrastructure, or a score of 2 if the country has strong containment capacity.

Other organizations assign their own ratings. The CDC uses a system of travel health notices with three levels (Watch, Alert, Warning). ECDC publishes threat assessments for the European region. Academic institutions like Johns Hopkins and the Georgetown Center for Global Health Science and Security produce independent risk analyses. None of these systems were designed to give you, a non-specialist, a single number that tells you what to do.

That's the gap PandemicAlarm fills. We synthesize inputs from multiple authoritative sources, weight them against a standardized rubric, and output a score that maps directly to individual preparedness actions.

Scoring happens within hours of a new outbreak being reported. Initial scores may carry more uncertainty because early data is always incomplete. PandemicAlarm flags this by noting when a score is based on limited information. As more data arrives, scores are updated accordingly.

What factors determine an outbreak's severity level?

Five primary factors drive the severity calculation: pathogen lethality, mode of transmission, geographic extent and velocity of spread, healthcare system capacity in affected areas, and availability of medical countermeasures. Each factor is weighted based on how much it influences the threat to individuals globally.

Pathogen lethality. Case fatality rate (CFR) is the starting point, but raw CFR can mislead. Ebola's historical CFR exceeds 50%, yet Ebola has caused far fewer total deaths than influenza, which has a CFR under 0.1%. Context matters. A CFR of 2% in a respiratory virus that spreads asymptomatically is far more dangerous at a population level than a CFR of 50% in a virus that only spreads through direct contact with bodily fluids. PandemicAlarm weights CFR against transmission efficiency to capture this distinction.

Transmission mode. Airborne and respiratory droplet transmission scores highest because it's hardest to contain. Contact transmission (requiring direct physical interaction) scores lower. Vector-borne transmission (requiring a mosquito or tick) scores lower still, since it can be addressed through vector control. COVID-19's airborne transmission made it almost impossible to contain once community spread began. Compare that with Ebola, which requires contact with infected bodily fluids and can be contained through rigorous infection control protocols.

Geographic spread and velocity. How many countries are affected, and how fast is it moving? An outbreak confined to one district in one country is fundamentally different from one that has appeared in 10 countries within a month. Speed matters as much as extent. A slow-moving outbreak in multiple countries might score lower than a fast-moving one in three countries, because velocity indicates whether containment is failing.

Healthcare capacity. The same pathogen poses different threats depending on where it appears. Marburg in Rwanda (strong health system, transparent reporting) played out very differently than Ebola in rural DRC (limited laboratory capacity, conflict zones, community distrust of health workers). PandemicAlarm factors in the Joint External Evaluation (JEE) scores that WHO assigns to countries based on their health security capabilities.

Countermeasures. Does an effective vaccine exist? Are antiviral treatments available? Is there sufficient global stockpile? When vaccines and treatments exist and are accessible, scores trend lower. COVID-19's severity score dropped from 5 to 3 in many assessments after effective vaccines became widely available in 2021. Conversely, a new pathogen with no vaccine, no treatment, and no natural population immunity will score higher even at low case counts.

How does severity scoring affect the response?

Severity scores shape responses at every level, from international organizations mobilizing emergency funding to you personally deciding whether to restock your medicine cabinet. Higher scores trigger faster resource allocation, more aggressive containment measures, and greater public attention, but the value of scoring is greatest at the individual level where you're making decisions with limited time and information.

At the institutional level, WHO uses its own risk assessments to determine resource deployment. A "very high" risk assessment triggers emergency response teams, funding requests, and coordination with affected countries. CDC adjusts its travel health notices based on outbreak severity, which directly affects whether the US government recommends or restricts travel to affected areas.

For you, severity scores serve as a decision filter. You cannot track every outbreak report from every source and make an informed judgment on each one. Severity scoring does that triage for you. When you open the PandemicAlarm map and see mostly green (Level 1-2) dots, you know the global situation is baseline. When an orange (Level 3) or red (Level 4-5) dot appears, you know exactly where to focus.

Real-world consequence: during COVID-19's escalation in January-February 2020, people who were using severity-based monitoring systems bought N95 masks at $1 each. By March, the same masks cost $10 or more, if you could find them. Antiviral medications, pulse oximeters, and hand sanitizer followed the same pattern. The information gap between "monitoring" and "panic buying" was about 6-8 weeks. Severity scores compress that gap into a single number.

A score change also tells you something important: direction. An outbreak that moves from Level 2 to Level 3 in a week is sending a clear signal. Containment isn't working. You should be paying closer attention and considering early preparedness actions, even if the outbreak is geographically distant. Direction of change often matters more than the current score.

What is the difference between severity and risk?

Severity measures how dangerous a disease event is in absolute terms: fatality rate, transmission speed, geographic scope, and overall impact. Risk measures how likely that event is to affect you personally, accounting for your location, health status, behavior patterns, and the specific countermeasures available to you. A high-severity event on another continent may pose low risk to you. A moderate-severity event in your own city is high risk regardless of its global score.

Think of it this way. Ebola in the DRC is a high-severity event. For a healthcare worker in Goma, it's also high risk. For someone in Toronto with no travel plans to Central Africa, the severity is unchanged but the personal risk is near zero.

PandemicAlarm reports severity, not personal risk, because personal risk depends on factors only you know. Your proximity to the outbreak, your immune status, your occupation, your travel plans, your household composition. But severity gives you the raw material to estimate your own risk.

Some guidelines for translating severity to personal risk:

A Level 3+ outbreak in a country you're planning to visit means your risk just went up significantly. Reconsider the trip or research specific precautions.

A Level 4+ outbreak anywhere in the world involving a respiratory pathogen means global spread is likely. Your risk will increase over time even if you're currently far from affected areas.

A Level 5 event means the pathogen has demonstrated the ability to spread globally. Your risk depends on your local situation, but assuming it won't reach you is not a safe bet. COVID-19 reached 196 countries and territories.

Age, chronic conditions, and immune status affect your risk within any severity level. A Level 3 influenza event is more dangerous for an 80-year-old with COPD than a healthy 30-year-old. Severity scoring doesn't capture individual vulnerability. You have to layer that judgment on top.

How can you use severity scores in your own preparedness?

Map each severity level to a specific set of actions you'll take, decide those actions in advance, and then follow your plan when a score changes instead of trying to figure out what to do in the moment. Pre-planned responses eliminate decision paralysis and ensure you act during the window when preparation is easiest and cheapest.

At Level 1-2: Maintain baseline readiness. Keep a rolling 2-week supply of shelf-stable food, water, prescription medications, and N95 masks. Check PandemicAlarm weekly. Read the report. Note the pathogen and location. No behavioral changes needed.

At Level 3: Shift to active monitoring. Check updates every 2-3 days. If you have travel to affected regions, research specific precautions or postpone. Top off your household supplies. Make sure your prescription medications are at a 90-day supply if your insurance allows. Review your family's communication plan. Confirm that everyone knows what to do if schools close or workplaces go remote.

At Level 4: Monitor daily. This is your last comfortable window. Purchase any remaining supplies at normal prices. Identify backup childcare, know your employer's remote work policy, and establish check-in protocols with elderly or immunocompromised family members. If the outbreak involves a respiratory pathogen, start carrying a mask in your bag even if you're not wearing it yet.

At Level 5: Execute your plan. If you prepared at Levels 3-4, you're set. Focus on information: track local case counts, follow public health guidance, reduce unnecessary exposure. You're watching data now, not scrambling for supplies.

Write your plan down. Literally write it. A laminated card on the fridge with "Level 3: top off pantry, refill prescriptions, check masks" is more useful in a crisis than any amount of knowledge stored in your head. Stress degrades memory and judgment. Your plan should not depend on either.

One more practice worth adopting: run a quarterly check. Every three months, verify your supplies haven't expired, update your contact lists, and review the current threat picture on PandemicAlarm. Fifteen minutes of maintenance prevents the frantic catch-up when a real event hits. For a deeper walkthrough of building your monitoring system, read our pandemic preparedness guide.

Frequently Asked Questions

How often do severity scores change?

Scores are updated whenever significant new data arrives, which can mean multiple times per week during an active outbreak. A sudden jump in cases, spread to a new country, or WHO declaring a PHEIC can all trigger a score change. During stable periods, scores may hold steady for weeks. PandemicAlarm timestamps every score change so you can see the trajectory.

Can two outbreaks of the same disease have different severity scores?

Yes. Severity depends on context, not just pathogen identity. Seasonal dengue in Thailand during monsoon season might score Level 1, while the 2023 dengue surge in Bangladesh scored Level 3 because it exceeded all historical records and overwhelmed hospitals. Same virus, very different situations.

Do other organizations use the same 1-5 scale?

No. PandemicAlarm's 1-5 scale is our own framework designed for individual decision-making. WHO uses qualitative risk categories (low, moderate, high, very high). CDC uses three-tier travel health notices. The Pandemic Severity Assessment Framework (PSAF), developed by CDC for influenza pandemics, uses a different methodology entirely. Our scale synthesizes multiple inputs into a single actionable number.

What happens when there's not enough data to assign a score?

Early-stage outbreaks often have incomplete data. PandemicAlarm assigns a provisional score based on available information and flags it as preliminary. A novel pathogen with unknown transmissibility but a high case fatality rate might receive a provisional Level 3 simply because the uncertainty itself warrants closer attention. Scores firm up as data accumulates.

Should I panic when I see a Level 4 or 5?

No. Panic leads to bad decisions. A Level 4 or 5 score means you should follow your preparedness plan, not improvise under stress. If you've maintained baseline readiness and have a written action plan for each level, a high score simply triggers the next step in your sequence. Calm beats fast every time.