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Multiple Studies Assess COVID-19 Vaccine Effectiveness and Evolving Disease Severity

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COVID-19 Vaccine & Disease Update: What the Latest Data Shows

A series of recent studies and expert analyses provide updated data on COVID-19 vaccine effectiveness against cardiovascular events and severe illness, as well as the disease's changing public health impact as population immunity rises.

Vaccine Effectiveness Against Cardiovascular Events

A study published in JAMA Internal Medicine on February 20, 2025, analyzed data from over 1 million U.S. veterans who received flu vaccinations at VA health care facilities in 2024. Approximately one-third of this group also received a COVID-19 vaccine.

Those who received a COVID-19 vaccine had a 38% lower risk of major cardiovascular events associated with documented COVID-19 infection within eight months following vaccination.

This benefit was most pronounced among individuals aged 75 and older and those with chronic conditions such as kidney and lung disease.

The same study reported an unexpected 24% reduction in all-cause major cardiac events among COVID-19 vaccine recipients, regardless of documented COVID-19 infection. The authors estimated this could translate to the prevention of approximately 3,500 major cardiac events and 2,400 deaths annually per 1 million people.

Lead author Ziyad Al-Aly suggested that undiagnosed COVID-19 infections may account for many cardiovascular events not attributed to the virus.

Study limitations: The predominantly older, white, and male composition of the veteran population (average age 70.1 years), and the study did not analyze variant-specific vaccine effectiveness.

Additional Effectiveness Findings

Another study in the same journal, led by Ryan Wiegand at the CDC, assessed the effectiveness of 2024-2025 COVID-19 vaccines. For adults aged 18 and older:

  • 41% effectiveness against critical illness
  • Reduced likelihood of COVID-19-associated emergency room or urgent care visits

Vaccine Effectiveness in European Populations

A third study, funded by the European Centre for Disease Prevention and Control and published in JAMA Network Open, evaluated individuals aged 60 and older across multiple European countries.

Approximately 55% effectiveness in preventing symptomatic disease in the two months following vaccination for the 2025-2026 season.

COVID-19 Disease Severity Trends

Multiple experts indicate that SARS-CoV-2 has become less threatening due to widespread immunity from infection and vaccination, though it continues to pose significant risk to elderly, immunocompromised, and very young individuals.

Key Epidemiological Data

  • COVID-19 dropped from the third leading cause of death among U.S. adults in 2021 to 15th in 2024
  • Among children, it fell out of the top 10 causes of death in 2023
  • CDC estimates 45,000–64,000 COVID-19 deaths in the U.S. (October 2024 – September 2025), with 13,000–40,000 in the seven months since then
  • Wastewater levels of SARS-CoV-2 are reported as the lowest ever recorded (though researchers note this could reflect fewer infections or reduced viral shedding)
  • Booster uptake in the U.S. was low for the 2025–2026 season:
    • 9.4% among children
    • 17.5% among adults
    • 22.1% among adults aged 65+
  • Gavi discontinued support for COVID-19 vaccine purchases at the end of 2025

Expert Assessments

Lia van der Hoek (Amsterdam UMC): The Omicron variant's emergence in late 2021, which causes milder disease and evades immunity, is the primary reason for reduced severity. She considers SARS-CoV-2 now "number 5 of the common cold coronaviruses."

Fiona Havers (Emory University): COVID-19 deaths are often attributed to non-specific causes like pneumonia, with modeling suggesting a declining trend. Severe disease now mainly affects age extremes, similar to other respiratory viruses.

Stanley Perlman (University of Iowa): Recent death numbers remain higher than expected, with unclear demographics of the deceased.

Alexandria Boehm (WastewaterSCAN): Low wastewater levels reported, and it remains to be seen if a summer surge will occur.

Malik Peiris (University of Hong Kong): SARS-CoV-2 is now "another seasonal respiratory virus."

Vineet Menachery (Emory): New strains are more capable of immune evasion but cause milder illness, putting them on par with common cold coronaviruses.

Ben Cowling (Hong Kong University): Not yet convinced COVID-19 is as minor as other coronaviruses, but it is on that trajectory.

Stanley Plotkin (vaccinologist): Most healthy people can control infection, while severe cases occur in those with poor immune responses, including very young and very old individuals.

Marion Koopmans (Erasmus University): For low-risk individuals, annual boosting may have little effect; for high-risk individuals, boosters still reduce hospitalization risk.

Policy Context

The U.S. CDC's Advisory Committee on Immunization Practices (ACIP), which was disbanded in June 2025, had been considering moving from universal to targeted recommendations for COVID-19 boosters. A new ACIP recommended in September 2025 that everyone aged 6 months and older could receive a shot if desired.

A study showing 50% reduction in emergency care and hospitalization from winter 2025 boosters was shelved by the Department of Health and Human Services (HHS), according to The Washington Post.

Public Health Commentary

Former FDA commissioner Robert Califf stated that the evidence shows the benefits of COVID-19 vaccines outweigh risks, particularly for high-risk individuals.

Study authors and commentators noted that despite lower uptake compared to flu vaccines, COVID-19 vaccines continue to provide protection against severe outcomes.