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Which COVID-19 shot causes fewer side effects? new study compares novavax and pfizer

NCT ID NCT06633835

Knowledge-focused Sponsor: Novavax Source: ClinicalTrials.gov ↗

What the study statuses mean

This study's is highlighted.

Recruitment status, easiest to join first

Recruiting now
This trial is taking on new participants right now.
Not yet recruiting
Registered, but not yet taking participants.
By invitation only
Not open to general applications. Only people the study team invites can take part.
Paused
Paused for now. It may or may not start again.
Ongoing
Running, but no longer taking on new participants.
Completed This study
The trial has finished. Results may not be published yet.
Stopped early
Stopped early, before it reached the end. That can be for many reasons, including safety.
Cancelled
Cancelled before anyone took part.

Expanded access (not trials)

Expanded access
Not a trial. This treatment can be requested outside a study, case by case, for people who qualify.
Expanded access (paused)
Not a trial. The treatment can normally be requested outside a study, but is unavailable right now.
Expanded access (ended)
Not a trial. The treatment could once be requested outside a study, but no longer can.
Approved
The treatment has been approved, so it is available normally rather than through this programme.

When the status isn't known

Details not published
The full record has not been published yet, so there is little to show here.
Status unknown
This status has not been confirmed recently, so it may be out of date.

First seen Jun 24, 2026 · Last updated Jun 27, 2026 · Updated 1 time

Summary

This completed study looked at how often healthcare workers and first responders experienced short-term side effects (like fever or sore arm) after getting either the updated Novavax or Pfizer COVID-19 vaccine. About 660 adults who had at least one prior COVID-19 shot took part. The goal was to see which vaccine caused fewer reactions in the first two days after vaccination.

What this could mean

Our plain-language read of the trial. This is informational only, not medical advice or a prediction.

Active substance
Novavax COVID-19 vaccine (protein subunit) and Pfizer mRNA COVID-19 vaccine
What this could lead to
If successful, this study could help people choose which COVID-19 vaccine might cause fewer short-term side effects.
What could go wrong
This is a completed observational comparison, not a test of whether the vaccines prevent disease. Results only cover the first two days after vaccination and may not apply to the general public.

This is an AI summary of the original study and may miss details. Read our disclaimer.

Study facts

What this study's own registry entry says, in plain language.

Phase

Phase 4

Runs after approval, following long-term safety and how well the treatment works in everyday use.

Participants

660 people

The number who actually took part.

Started

Sep 2024

Finished

Jun 2025

Lead sponsor

A company

The lead sponsor is a pharmaceutical, biotech, or medical-device company.

Who can take part

This study's own entry requirements. Only the study team can say for certain whether you qualify.

Ages

18 years and older

Sex

Anyone

Healthy volunteers

Accepted

You do not need to have the condition being studied to take part.

Show the full entry requirements

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * Adults aged 18 years and older who have received at least one COVID-19 vaccination in the past 4 years * Health care workers or first responders who have direct face-to-face contact, defined as being within 3 feet, or about an arm's length, with patients as part of their full-time or part-time (greater than or equal to 20 hours per week) job responsibilities * Intends to receive a dose of the updated 2024-25 COVID-19 vaccine * Able to understand and provide informed consent * Comfortable reading and responding to text messages and emails sent in English or having an interpreter assist them * Able and willing to comply with all study requirements * Access to a smartphone, tablet, or computer to complete the consent, screener and study questionnaires Exclusion Criteria: * Ongoing participation in other vaccine or investigational product trials within 90 days of study enrollment * History of self-reported severe allergic reaction to prior COVID-19 vaccine * Receipt of COVID-19 vaccine within 60 days of enrollment * Plans to receive additional vaccines within 7 days after the vaccination visit for study enrollment. (Co-administered vaccinations at time or day of COVID-19 vaccination are permissible)

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Conditions

The condition(s) this trial relates to.

COVID-19 Vaccine-Preventable Diseases

As listed by the trial registrant

The condition terms exactly as the trial's registrant entered them.

COVID -19 SARS-CoV-2 infection Vaccine-preventable diseases

Contacts and locations

Locations

  • University of Utah School of Medicine

    Salt Lake City, Utah, 84108, United States

More trials for these conditions

Other studies related to the condition(s) this trial covers.