Understanding Flu and COVID Vaccine Studies

vaxopedia.org

Mar 26, 2026

Have you ever wondered why flu and COVID vaccine studies aren’t as perfect as anti-vaccine influencers want them to be?

Is Alex Berenson going full anti-vaccine?

After all, there are plenty of flu and COVID vaccine studies that say they are safe and effective.

Understanding Flu and COVID Vaccine Studies

Of course, none of those studies are good enough for folks like Alex Berenson and other anti-vaccine influencers.

Ironically, most seem to love any study that says vaccines are harmful or don’t work, even the ones that get retracted!

Still, it is important to understand that flu and COVID vaccine studies do have some limitations.

Why?

It seems that it is mostly because:

the studies typically have to be completed during a single season, because flu and COVID viruses quickly change, and you want the strain to be (hopefully) matched to the vaccine you are giving
even within that season, many of the cases occur during a short window of peak cases and that makes it hard to find everyone who has the flu
flu and COVID symptoms are very variable, in fact, some people are infected and have no symptoms at all and people with mild symptoms might not seek treatment and could be missed

And no, you can’t do a randomized, placebo controlled double-blind flu vaccine clinical trial.

“So-called "universal vaccine recommendations" introduce ethical challenges in performing RCTs that assign people to a placebo group, which could place them at elevated risk for serious complications from flu. Also, observational studies often are the only option to measure vaccine effectiveness against more severe, less common flu outcomes, such as hospitalization.”
How Flu Vaccine Effectiveness and Efficacy Are Measured

Why not?

“Requiring placebos for improved vaccine variants would needlessly expose research participants to deadly diseases for which effective vaccines are available. Placebo testing is therefore not appropriate for already approved vaccines and should only be done when no other options exist and a fatal epidemic is looming against which only a novel vaccine would be available.”
Fool’s-gold science

Mostly because it is not ethical, but also because observational studies are thought to be better for this purpose.

“The challenges of estimating influenza VE are numerous and complex. Evidence continues to suggest that influenza vaccines are protective against infection; however, depending on the season, vaccine, and study, estimates of VE vary.”
Challenges in estimating influenza vaccine effectiveness

Nonetheless, even with all of these known issues, current evidence does show that flu and COVID vaccines work.

Maybe not perfectly, but they work well enough that you shouldn’t hesitate to get vaccinated and protected with a flu vaccine each year and a COVID vaccine if you are high risk.

The RSV vaccine works well too!

“Ongoing peer-reviewed evidence supports the safety and effectiveness of immunizations against Covid-19, RSV, and influenza during the 2025–2026 season.”
Updated Evidence for Covid-19, RSV, and Influenza Vaccines for 2025-2026

Not surprisingly, these studies also show that all of these vaccines are safe, with few risks.

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Mike S

Mar 27Edited

It took me 2 minutes using a search engine to find reference to studies in kids that not only were RCTs with placebo, but placebo consisting of normal saline (0.9% NaCl). This was quadrivalent flu vax versus trivalent flu vax versus saline placebo.

"Children from 6 to 35 months -

In one study, 1614 children from 6 to 35 months of age received 2 doses (0.5 mL) of Vaxigrip Tetra, 1612 received 2 doses (0.5 mL) of placebo (NaCl 0.9%) and 367 received 2 doses (0.5 mL) of Vaxigrip."

https://www.tga.gov.au/sites/default/files/auspar-inactivated-quadrivalent-influenza-vaccine-split-virion-191219-pi.pdf