Written By: Mrs. Mayuri Mathur

Published On: 02 Jun, 2025 6:57 PM | Updated On: 02 Jun, 2025 7:15 PM

Vaccinated but Still Got COVID? Here’s Why That Happens

You’ve done your part—got the COVID-19 vaccine, maybe even a booster or two—yet you still ended up with a positive test. Frustrating? Definitely. But alarming? Not necessarily. Breakthrough infections (i.e., COVID-19 in vaccinated individuals) are expected and signal that the vaccines are working as intended: to prevent severe disease, not always infection itself.

Here’s what’s really going on—and why getting vaccinated is still one of the smartest moves you can make.

• COVID-19 and the Impact of Vaccination

Since the World Health Organization (WHO) declared COVID-19 a global pandemic in March 2020, the virus has affected millions of lives worldwide. Vaccination efforts have played a critical role in reducing the severity of illness, hospitalizations, and deaths. Additionally, studies have shown that vaccines can enhance natural immunity—particularly in individuals who have recovered from COVID-19—with some research indicating that strong protection can last over a year when vaccination follows infection. As a result, health experts strongly recommend vaccination for everyone, including those who have previously contracted the disease.

• Why Do Breakthrough Infections Happen?

Getting COVID despite being vaccinated isn’t a sign of failure—it’s proof that your immune system is actively fighting the virus. The combination of vaccination and recovery from a mild breakthrough infection creates what scientists call hybrid immunity, which offers broader and more durable protection than either vaccination or recovery from a mild breakthrough infection alone.

1. No Vaccine Offers 100% Protection Against Infection

COVID-19 vaccines are highly effective but not infallible. Most are designed to train the immune system to recognize and respond to the SARS-CoV-2 virus, especially its spike protein. However, as the virus evolves and new sub variants emerge (such as XBB.1.5, EG.5, or JN.1), mutations in the spike protein can reduce the ability of antibodies to recognize and neutralize it. 

While mRNA vaccines initially demonstrated nearly 95% efficacy in preventing symptomatic infection, their real-world effectiveness, especially against newer variants, has focused more on reducing the risk of hospitalization, ICU admission, and death.

2. Immunity Can Wane Over Time

The immunity gained from vaccination—or even prior infection—fades over time. Studies show that protection against symptomatic infection starts to decline around 4–6 months after the last dose. That’s why booster doses are recommended, especially for vulnerable populations.

Breakthrough infections are more likely the longer it’s been since your last dose. However, even as protection against mild infection decreases, defense against severe outcomes remains strong with timely boosters.

3. The Virus Is Evolving

SARS-CoV-2 continues to evolve rapidly, giving rise to new variants that spread more easily and are increasingly capable of evading the immune system. Since late 2021, Omicron and its subvariants have remained dominant, mainly due to changes in the spike protein that enable them to cause more breakthrough infections, even in vaccinated individuals.

Image Source: BMC

However, vaccination still makes a crucial difference. People who are vaccinated typically experience milder symptoms, shorter illness duration, and a faster recovery due to the immune system’s “memory” response.

4. Vaccines Focus on Severity, Not Prevention

It’s essential to recognize that vaccines do not provide impenetrable barriers. Instead, they function as immunological training tools, priming the immune system to recognize and respond more efficiently to the SARS-CoV-2 virus. Upon exposure, a vaccinated individual’s immune system can mount a faster and more effective response, significantly lowering the risk of severe disease, hospitalization, and long-term complications.

A meta-analysis published in The Lancet found that COVID-19 vaccination significantly reduces the risk of hospitalization (by 89%) and death (by 91%) even when breakthrough infection occurs.

5. Building Immunity Takes Time

It takes approximately two weeks for your body to build strong protection after each dose. That protection is strongest in the first few months after vaccination and then gradually declines over time. The duration of protection varies based on your vaccine type, past infections, and circulating virus strains.

• So, What Happens During a Breakthrough Infection?

For most vaccinated individuals, breakthrough infections result in:

• Mild symptoms (fever, fatigue, sore throat, congestion)

• Shorter duration of illness

• Lower viral load, leading to less transmission risk (especially with boosters)

• Stronger and more hybrid immunity after recovery

In rare cases, especially among immunocompromised or elderly individuals, symptoms may be more pronounced—which is why booster strategies remain crucial for these groups.

• What to Do Next

In September 2024, the World Health Organization's Strategic Advisory Group of Experts (SAGE) reaffirmed the importance of COVID-19 vaccination, especially for individuals at a higher risk of severe illness or death.

Image Source: APP

Revaccination (a booster dose) is especially recommended for these groups, around 12 months after the last dose, to maintain protection.

1. Updated Vaccination Recommendations

WHO’s advice is based on two main factors:

1. Your age and health condition

2. Your previous vaccination history

Even if you've had COVID-19 before, get vaccinated when a dose is offered. Having both infection-acquired and vaccine-acquired immunity (hybrid immunity) offers stronger, longer-lasting protection.

2. Don’t Wait for Newer Vaccines

Don’t delay your shot while waiting for updated vaccine versions. All currently approved vaccines, including the original and bivalent types, continue to provide adequate and effective protection against severe disease.

Newer vaccines targeting emerging variants may become available, but for now, any available vaccine is better than no vaccine—especially for individuals at high risk.

3. Continue Protecting Yourself and Others

Even after vaccination, COVID-19 can still be transmitted. To reduce the spread and protect those around you:

• Wash your hands often, especially after being in public spaces

• Cover your mouth and nose when coughing or sneezing

• Follow public health advice from your local authorities

• Keep up with booster doses, especially if you’re in a high-risk group

• Isolate quickly if you test positive to avoid infecting others

• Treat symptoms at home if they’re mild—seek care if they worsen

• Wear a mask in crowded or high-risk settings, especially during waves or outbreaks

Image source: CDC

References

1. Asadi-Pooya AA, Nemati M, Shahisavandi M, Nemati H, Karimi A, Jafari A, Nasiri S, Mohammadi SS, Rahimian Z, Bayat H, Akbari A, Emami A, Eilami O. How does COVID-19 vaccination affect long-COVID symptoms? PLoS One. 2024 Feb 7;19(2):e0296680. doi: 10.1371/journal.pone.0296680. PMID: 38324547; PMCID: PMC10849259.https://pmc.ncbi.nlm.nih.gov/articles/PMC10849259/

2. CDC. (2023). Omicron Variant: What You Need to Know. https://www.cdc.gov/coronavirus/2019-ncov/variants/omicron-variant.html 

3. Polack, F. P., et al. (2020). Safety and Efficacy of the BNT162b2 mRNA Covid-19 Vaccine. NEJM, 383:2603–2615. 

4. Tenforde, M. W., et al. (2021). Effectiveness of COVID-19 Vaccines in Preventing Hospitalization. MMWR, 70(34):1156–1162. 

5. Chemaitelly, H., et al. (2021). Waning of BNT162b2 Vaccine Protection against SARS-CoV-2 Infection in Qatar. NEJM, 385:e83. 

6. Bar-On, Y. M., et al. (2021). Protection of BNT162b2 Booster against Covid-19 in Israel. NEJM, 385(15):1393–1400. 

7. Cao, Y., et al. (2022). Omicron escapes the majority of existing SARS-CoV-2 neutralizing antibodies. Nature, 602:657–663. 

8. Andrews, N., et al. (2022). Effectiveness of COVID-19 booster vaccines against Omicron-related severe outcomes. The Lancet, 399(10324):1303–1312. 

9. Levine-Tiefenbrun, M., et al. (2021). Decreased SARS-CoV-2 viral load following vaccination. Nature Medicine, 27(5):790–792. 

Goldberg, Y., et al. (2022). Protection and waning of natural and hybrid immunity. NEJM, 386:2201–2212.