COVID-19 Is Not Over: What Thailand’s Vaccination Data Tells Us About Who Needs Protecting Now
A new modelling study using updated 2024 Thai epidemiological data projects that vaccinating older adults and high-risk groups could prevent over 318,000 infections, 9,000 hospitalisations, and 1,000 deaths in a single year — and that coverage rates are the biggest lever available to policymakers.
The global emergency declaration ended in May 2023. But COVID-19 never stopped. The virus continues to circulate, evolve, and cause hospitalisations and deaths — particularly among older adults and people with underlying health conditions. The question for health policymakers is no longer whether COVID-19 is a crisis, but how much ongoing harm can realistically be prevented through strategic, sustained vaccination. A new study from Thailand has tried to put numbers on exactly that.
Published in Pulmonary Therapy, this peer-reviewed modelling study uses freshly updated Thai epidemiological data from 2024 to project the health and economic impact of different COVID-19 vaccination strategies. The findings are striking: even modest vaccination coverage among the right populations could prevent hundreds of thousands of infections and generate billions of Thai baht in savings — and there is enormous room to do more.
Thailand’s COVID-19 Burden: The Context
Thailand has recorded nearly 5 million COVID-19 cases and over 34,000 deaths since the pandemic began. The country navigated multiple distinct waves — first Alpha, then a prolonged Delta peak in mid-2021, before the Omicron variant displaced all prior strains by early 2022 and has dominated since. Thailand’s national vaccination campaign was one of Asia’s most ambitious, reaching 77.6% double-dose coverage by December 2022.
Yet uptake of subsequent booster doses has remained low, and the population’s immunity — from both prior infection and vaccination — wanes over time. In 2026, Thailand’s Ministry of Public Health recommends annual COVID-19 vaccination for high-risk groups: adults aged 60 and over, those with chronic conditions (heart disease, diabetes, kidney disease, respiratory conditions, stroke, immunocompromising conditions), pregnant women, healthcare workers, and caregivers of vulnerable people.
Since the end of the global health emergency in 2023, routine surveillance and testing have declined dramatically. A 2025 study estimated that Thailand’s true COVID-19 infection rate is approximately 22.7 times higher than officially reported cases — based on the median underreporting factor for East and Southeast Asia during the Omicron BA.4/BA.5 period. The researchers adjusted all infection data using this factor, meaning the actual disease burden is far larger than headline numbers suggest.
How the Study Was Conducted
The researchers used a validated decision tree–Markov model originally developed for the United States and previously adapted for Thailand in 2023, now recalibrated with 2024 data. The model tracks individuals through a range of COVID-19 health states — from susceptibility through infection, symptomatic illness, outpatient care, hospitalisation, ICU admission, mechanical ventilation, long COVID, and death — over a one-year period.
- Vaccine effectiveness: 50% against infection, 60% against symptomatic infection, 70% against severe disease — based on real-world evidence from Omicron-adapted vaccines
- Duration of protection: 6 months, with effectiveness waning at a rate of 1/duration per month (scenario analyses tested 4-month and 12-month durations)
- Baseline coverage assumption: 20% of eligible population vaccinated — conservative, reflecting current real-world uptake levels
- Long COVID: Base probability of 16.5%, adjusted by vaccination status and hospitalisation (from Singapore data, applied across all age groups due to lack of Thailand-specific data)
- Population: Thailand’s full population stratified into 8 age groups and 2 risk groups (standard-risk and high-risk/60+)
- Underreporting factor: 22.7 applied to reported attack rates to reflect estimated true infection burden
The Five Vaccination Strategies Tested
The Base Case Results: What Targeted Vaccination Achieves
At the base-case assumption of 20% coverage among those aged 60 and over and high-risk individuals aged 6 months to 59 years, the model projects substantial public health and economic gains:
Notably, the reduction in deaths (31%) is proportionally larger than the reduction in infections (15%) — which makes intuitive sense. The strategy targets the individuals most likely to develop severe disease, so the same number of vaccine doses has a disproportionately large impact on mortality and hospitalisation relative to total case counts.
The Coverage Lever: Why 50% Is So Much Better Than 20%
One of the most policy-relevant findings is how sensitive projected outcomes are to vaccination coverage. The model tested increasing coverage from the base case of 20% to 30%, 40%, and 50% — keeping the same eligible population (60+ and high-risk). The results scale in a near-linear fashion:
This is a crucial finding for policymakers: doubling coverage from 20% to 40% doubles every projected health benefit. Deaths averted, hospitalisations prevented, infections stopped, and money saved all scale proportionally. The marginal return on investment from reaching more eligible people is very high.
What Happens When Younger Adults Are Included
Expanding eligibility from the base case (60+ and high-risk) to include younger standard-risk adults yields significantly greater total benefits — though the incremental gains in deaths averted are smaller than the gains in infections and hospitalisations, reflecting the lower severity risk of younger, standard-risk individuals.
| Strategy | Deaths Averted | Hospitalisations Averted | Infections Averted | Direct Cost Savings (THB M) |
|---|---|---|---|---|
| 60+ & High-Risk (Base) | 1,061 | 9,147 | 318,700 | 3,300 |
| 60+ only | 1,030 | 6,955 | 177,168 | 1,968 |
| 50+ & High-Risk | 1,094 (+3%) | 10,804 (+18%) | 381,370 (+20%) | 3,933 (+19%) |
| 18+ & High-Risk | 1,116 (+5%) | 14,395 (+57%) | 739,083 (+132%) | 7,176 (+117%) |
| Universal (6 months+) | 1,118 (+5%) | 15,788 (+73%) | 840,419 (+164%) | 8,111 (+146%) |
The data illustrate a clear pattern: expanding to younger adults dramatically reduces total infections and hospitalisations but adds comparatively little to deaths averted. This is because most COVID-19 deaths are concentrated in older and high-risk populations. Policymakers prioritising mortality reduction should focus on the 60+ group; those aiming to reduce health system pressure and economic burden will find the greatest gains by including working-age adults.
Vaccine Duration Matters Too: The Scenario Analyses
The model also tested how projected outcomes change depending on how long vaccine protection lasts — a critical real-world variable that is not fully predictable with evolving variants.
Deaths averted increase by 40%, hospitalisations by 42%, infections by 42%, and total costs averted by 42%. A vaccine that protects for 12 months rather than 6 months is, effectively, twice as valuable from a public health perspective — even without changing coverage at all.
When only protection against severe disease lasts 12 months (while infection protection remains at 6 months), hospitalisations averted increase by 41% and deaths by 6% — with virtually no change in infection counts. This scenario is plausible given that vaccines have historically shown more durable protection against severe outcomes than against mild infection.
If protection lasts only 4 months instead of 6, all projected health and economic benefits decrease by approximately 24–25%. This underscores how important vaccine durability is — and why ongoing monitoring of real-world effectiveness against circulating strains matters for policy planning.
The Barriers to Actually Reaching 50% Coverage
The researchers are candid that the modelled coverage scenarios are projections, not guarantees. Real-world uptake depends on factors well beyond the model’s scope. The study explicitly flags several implementation realities that policymakers must address:
- Vaccine hesitancy and reduced perceived risk — as COVID-19 recedes from the emergency phase, public motivation to vaccinate tends to decline, even among high-risk groups
- Operational constraints — procurement planning, healthcare workforce capacity, and cold-chain logistics all affect real-world delivery
- Integration with seasonal respiratory campaigns — aligning COVID-19 vaccination with annual influenza programmes may improve efficiency and uptake simultaneously
- Communication and outreach — expanded public health messaging, particularly targeting older adults and those with chronic conditions, requires investment but improves impact
- Alternative delivery platforms — pharmacies, community health workers, and workplace programmes can dramatically expand reach beyond traditional clinic settings
A Word on the Funding and Conflict of Interest
This study was sponsored by Pfizer, and several authors are Pfizer employees. The study models an “adapted COVID-19 vaccine” and the findings naturally support the case for continued vaccination programmes. Readers and policymakers should weigh this context when interpreting the results. That said, the underlying model is a validated, peer-reviewed framework applied with published Thai data, and the qualitative direction of the findings — that higher coverage among high-risk groups reduces disease burden — is consistent with the broader independent evidence base for COVID-19 vaccination.
What the Study Cannot Tell Us
The researchers acknowledge several important limitations. The model uses a static structure rather than a dynamic transmission model, meaning it does not capture herd immunity effects — so projected benefits are likely conservative underestimates. Long COVID data came from Singapore rather than Thailand, introducing potential inaccuracies. ICU and mechanical ventilation probabilities came from a different time period than hospitalisation data. And the underreporting factor of 22.7 — while evidence-based — introduces significant uncertainty into all infection projections.
Key Takeaways from the Research
- COVID-19 vaccination in Thailand still generates large, measurable public health returns: Even at 20% coverage targeting 60+ and high-risk individuals, the model projects over 318,000 infections, 9,000 hospitalisations, and 1,000 deaths prevented in a single year
- Coverage is the most powerful available lever: Increasing coverage from 20% to 50% amplifies every projected health benefit by 150% — doubling the doses administered doubles the lives saved
- Older adults deliver the highest return on vaccination investment: The mortality reduction from targeting 60+ is disproportionately large relative to the coverage required, reflecting the concentration of severe disease in this group
- Expanding to younger adults reduces health system burden dramatically: Including adults aged 18+ more than doubles projected hospitalisations averted and more than doubles direct medical cost savings — even though deaths averted increase by only 5%
- Vaccine durability matters as much as coverage: A vaccine that protects for 12 months rather than 6 months delivers 40% more public health benefit without any additional doses — making duration of protection a critical procurement criterion
- Thailand’s true infection burden is vastly underreported: With a 22.7× underreporting factor, the visible case counts represent a fraction of actual transmission — meaning the ongoing rationale for vaccination is far stronger than reported numbers suggest
COVID-19 has entered the endemic phase, but endemic does not mean harmless. The experience with influenza — a virus that kills tens of thousands of Thais annually despite decades of familiarity — is a useful reference point. Annual, well-targeted, high-coverage vaccination remains one of the most cost-effective tools available to prevent avoidable deaths, reduce healthcare system strain, and protect economic productivity.
