Question explored with the scientific record
Do covid vaccines work?
The short version: yes, for severe disease and death, in the first months after a dose, for adults. No, not durably, and not for infection.
The evidence for benefit is real but time-limited. A 2024–2025 US hospital study found updated vaccines cut COVID hospitalization by about 40% and cut the need for a breathing tube or death by about 79% [19]. A Norwegian study of 4.6 million adults found people with three or more mRNA doses had roughly 60% lower all-cause death rates than unvaccinated people across every age group [44]. A Hungarian nationwide study of 6.4 million adults found all six vaccines reduced all-cause mortality, after correcting for the healthy-vaccinee effect [33]. These are the strongest studies in the pile: large, population-based, hard endpoints.
The weakness is durability and infection. Effectiveness against Omicron infection wanes fast. One study showed three-dose protection against BA.2 falling from 61% at one month to negative after five months [14]. A 2025 Egyptian study of health workers found no significant protection from vaccination alone against symptomatic infection, with wide confidence intervals that included zero [5]. A 2025 Chinese study of adults 60 and older found only about 42% protection against symptomatic JN.1 infection, and essentially none in people 75 and older [4]. The most informative comparison, vaccinated versus unvaccinated over years, is rarely run. When it is, the results are mixed: a US county study found higher vaccine uptake tracked with higher all-cause excess mortality in 2022 and 2023, though the design cannot prove causation [25].
| Outcome | Best evidence | Result |
|---|---|---|
| Hospitalization (2024–25) | US test-negative study [19] | ~40% reduction |
| Ventilator or death (2024–25) | US test-negative study [19] | ~79% reduction |
| All-cause death (3+ doses) | Norway cohort [44] | ~60% lower rate |
| Symptomatic JN.1 infection, 60+ | China cohort [4] | ~42% reduction |
| Symptomatic infection, HCWs | Egypt cohort [5] | not significant |
The safety data is thinner than the efficacy data. The manufacturer-funded trials measured antibody titers, not long-term outcomes. Passive surveillance systems detect almost nothing by design. A 2022 Danish study of 101,786 heart failure patients found no increased risk of worsening heart failure, myocarditis, or blood clots within 90 days [23], but that is a short window. The long-term picture, especially for repeated boosting, is simply not established by the evidence here.
My call: for older adults and high-risk people, the vaccines reduce severe disease and death for a few months after a dose. For healthy younger people, the benefit against infection is modest and short-lived, and the long-term safety data does not exist. Confidence: moderate.
Sources used 8
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WSK-V102C COVID-19 vaccine effectiveness against SARS-CoV-2 JN.1 symptomatic infection among adults 60 years and older: a prospective observational cohort study in Shaanxi Province, China, 2024
Boosting with WSK-V102C in adults 60+ in Shaanxi, China, provided moderate protection against symptomatic SARS-CoV-2 JN.1 infection (adjusted VE ~42%), particularly among 60–74-year-olds (~50%), over a six-month real-world follow-up, with no hospitalizations or deaths observed.
DOI: 10.1186/s12889-025-25750-1 -
Assessing SARS-CoV-2 vaccine effectiveness in health workers: a cohort study conducted during the pandemic decline phase in five hospitals, affiliated to Al-Azhar University- Egypt
A WHO-supported, multicenter prospective cohort study at five Al-Azhar University hospitals in Egypt evaluated SARS-CoV-2 vaccine effectiveness against symptomatic RT-PCR-confirmed infection among healthcare workers over about one year, finding no significant protection overall …
DOI: 10.1186/s12879-025-11446-9 -
Effectiveness of mRNA-1273 vaccination against SARS-CoV-2 omicron subvariants BA.1, BA.2, BA.2.12.1, BA.4, and BA.5
This study evaluates the effectiveness of the mRNA-1273 vaccine against SARS-CoV-2 omicron subvariants, revealing that while three-dose effectiveness against BA.1 infection is high, effectiveness against BA.2, BA.4, and BA.5 wanes rapidly, with four-dose effectiveness also showi…
DOI: 10.1038/s41467-023-35815-7 -
Estimated Effectiveness of 2024-2025 COVID-19 Vaccination Against Severe COVID-19
Updated 2024-2025 COVID-19 vaccines reduced COVID-19–associated hospitalization by about 40% and prevented invasive mechanical ventilation or death by about 79% among adults, with similar protection across KP.3.1.1, XEC, and LP.8.1 lineages and detectable protection for up to 3–…
DOI: 10.1001/jamanetworkopen.2025.57415 -
Risk of worsening heart failure and all-cause mortality following mRNA COVID-19 vaccination in patients with heart failure: a Danish nationwide real-world safety study
In a nationwide Danish cohort of 101,786 patients with heart failure, SARS-CoV-2 mRNA vaccination was associated with a lower 90-day all-cause mortality risk compared with a matched 2019 unvaccinated cohort and with no difference in worsening heart failure, myocarditis, or venou…
DOI: 10.1093/eurheartj/ehac544.881 -
Why COVID-19 vaccination cannot be ruled out as an explanation for all-cause excess mortality in the pandemic’s aftermath: A population-level study of over 3,000 US counties with over 320 million people
A US county-level study found positive associations between per-capita COVID-19 vaccine uptake and all-cause excess mortality in 2022 and 2023, even when adjusting for lagged mortality, but the design cannot establish causation.
DOI: 10.12688/f1000research.177279.1 -
Effectiveness of COVID-19 Vaccination in Preventing All-Cause Mortality among Adults during the Third Wave of the Epidemic in Hungary: Nationwide Retrospective Cohort Study
In a nationwide retrospective cohort of 6.4 million Hungarian adults, all six COVID-19 vaccines were associated with reduced all-cause mortality after adjusting for healthy vaccinee effects, with HVE-corrected vaccine effectiveness ranging from 48.7% for Pfizer-BioNTech to 75.4%…
DOI: 10.3390/vaccines10071009 -
COVID-19 mRNA vaccination and all-cause mortality in the adult population in Norway during 2021–2023: a population-based cohort study
In a Norwegian population-based cohort of 4,645,910 adults followed from January 2021 to December 2023, individuals who received three or more mRNA vaccine doses had a substantially lower adjusted all-cause mortality rate than unvaccinated individuals, with fully vaccinated adul…
DOI: 10.1136/bmjph-2024-001859