Two is better than one: Combined COVID-19 and flu vaccination offers best shot for avoiding long COVID

The study presents a timely reminder of the far-reaching benefits of vaccination.

(April 2025) As the world moves on from the acute phase of the COVID-19 pandemic, long COVID continues to cast a long shadow.

Despite milder variants and widespread vaccination, it is estimated that at least 10% of those ever infected with COVID—especially older adults—still suffer from lingering symptoms: fatigue, brain fog, joint pain, memory loss, sleep disturbances and more.

At the same time, vaccine hesitancy is on the rise in many countries, and some national collaborations around flu vaccination have been scaled back. This makes recent findings from SHARE data all the timelier.

A cross-national study of older adults last April 2024 found that the best protection against long COVID came from receiving both the flu and COVID-19 vaccines. While each vaccine offered some individual protection, the combination was most effective.

The study, led by Wenyan Wu and colleagues and published in Human Vaccines & Immunotherapeutics, used data from SHARE (Survey of Health, Ageing and Retirement in Europe), covering 28 countries and focusing on individuals aged 50+. This group is at higher risk for both severe COVID-19 and long COVID, making it an ideal population for studying protective effects.

Could the Flu Vaccine Help Fight Long COVID?

We know that the COVID vaccination reduces the risk of severe illness and death in COVID-19 – and research goes further to suggest that vaccines may also reduce the risk of developing long COVID.

But surprisingly, there’s even a growing body of evidence suggesting that the influenza vaccine can do the same.

This effect is tied to the concept of trained immunity – the name given to the immune system’s ability to ‘remember’ past infections or vaccinations, even when they involve different pathogens. It’s thought the flu vaccine primes the innate immune system, making it more responsive and efficient at recognising and responding to new infections.

Vaccines essentially expose your immune system to pathogens it’s never encountered before, providing a practice drill to recognise and combat the real threat when it comes.

The flu shot may give the immune system a helpful boost that carries over into its fight against COVID-19.

What Happens When You Combine Flu and COVID-19 Vaccines?

The SHARE study, which includes data from 27 European countries and Israel, provides a unique opportunity to examine the relationship between vaccination and long COVID in a large representative sample. The study focuses on individuals aged 50 and over, a group at higher risk for both severe COVID-19 and long COVID. By analysing data from Waves 8 and 9 of the SHARE survey, along with the SHARE Corona Survey, the study offers valuable insights into how vaccination may influence the development of long COVID.

Researchers used SHARE data from 28 countries to analyse over 1,900 individuals with full vaccination records. They divided them into four groups:

Vaccinated for both flu and COVID-19
COVID-19 only
Flu only
Neither

They then looked at who developed long COVID, defined as the persistence of COVID-19-related symptoms for at least two months after the initial infection.

The Results: Best Protection with Both Shots

The group who received both vaccines had the lowest incidence of long COVID. While both vaccines individually offered some level of protection, the combined approach appeared to offer the greatest benefit.

Why This Matters Now

As flu and COVID-19 vaccinations are increasingly administered together in public health programmes, this finding strengthens the case for integrated vaccination strategies, especially for older adults.

Findings like this underline just how far the benefits of vaccination can reach — and how small actions, like getting your flu jab, might offer unexpected protection down the line.

Study by Wu, W., Zheng, X., Ding, H., Miao, T., Zang, Y., Shen, S., & Gao, Y. (2024). Association between combination COVID-19-influenza vaccination and long COVID in middle-aged and older Europeans: A cross-sectional study. Human Vaccines & Immunotherapeutics, 20(1). DOI: 10.1080/21645515.2024.2345505

URL: https://doi.org/10.1080/21645515.2024.2345505