COVID-19: Understanding What We Know After Five Years

Five years after COVID-19 transformed everyday life around the world, our understanding of the disease has changed considerably.

SARS-CoV-2 is still circulating, but COVID-19 today is very different from the early pandemic years. Immunity from vaccination and previous infections has changed the risk landscape, treatments have improved, and health systems have learned much more about who is most vulnerable.

But COVID-19 has not disappeared.

What have we learned?

1. COVID-19 can still become serious

For many people, infection is mild or moderate. But older adults and people with certain underlying health conditions remain at greater risk of hospitalization and severe disease.

Vaccination continues to provide meaningful protection against severe illness, hospitalization, and death. Protection against infection itself is less durable and changes as the virus evolves. (CDC)

2. The virus continues to evolve

SARS-CoV-2 has produced successive variants and subvariants. This is one reason COVID-19 vaccines are periodically updated—to better match viruses currently circulating.

The goal of vaccination is not necessarily to guarantee that someone will never become infected. A major goal is reducing the likelihood of severe disease and its complications. (CDC)

3. Long COVID is real

One of the most important discoveries of the past five years has been the recognition of Long COVID.

Some people develop symptoms or health problems that persist, return, or appear after the initial infection. These can involve multiple body systems and may last months or even years. There is currently no single laboratory test that can definitively diagnose Long COVID. (CDC)

Research also indicates that vaccination can reduce the risk of developing Long COVID. (CDC)

4. Prevention is now more individualized

COVID-19 prevention no longer looks exactly the same for everyone.

Someone who is older, immunocompromised, or has medical conditions that increase the risk of severe COVID-19 may benefit substantially from additional protection. For healthier younger people, the balance of risks and benefits can be different.

For the 2025–2026 season in the United States, CDC guidance uses individual/shared clinical decision-making for COVID-19 vaccination, with particularly strong emphasis on people at increased risk of severe disease. (CDC)

5. Previous infection isn’t permanent protection

Having COVID-19 can provide some immunity, but that protection varies and decreases over time. Reinfection is possible, and each infection carries some risk of complications, including Long COVID. (CDC)

What should we remember?

Five years of evidence has taught us that COVID-19 isn’t simply a story of either “nothing to worry about” or “everything is dangerous.”

The reality is more nuanced.

For most people, the risk of severe illness is considerably lower than it was during the earliest stages of the pandemic. At the same time, COVID-19 continues to cause serious illness and remains particularly important for vulnerable populations.

The most useful approach is to stay informed, pay attention to current local guidance, seek medical advice promptly if you are at high risk and become ill, and make vaccination decisions based on your age, health, previous infections, and individual risk.

Five years later, perhaps the biggest lesson is this: COVID-19 became less predictable when we treated everyone as having exactly the same risk. Understanding who is most vulnerable—and protecting those people—is one of the most important things we have learned. (CDC)