Does the Novavax COVID-19 cause fewer side effects?


The Novavax COVID-19 vaccine (Nuvaxovid) causes slightly fewer side effects on average, but the difference is modest at best.

People who get the Novavax shot are somewhat less likely to report symptoms at the injection site (e.g. soreness) or throughout the body (e.g. fatigue). Mild to moderate side effects are still very common with Novavax. Regardless of which vaccine you get, your arm may feel a little sore and you may feel a bit off for a day or two. A small price to pay for strong protection!

As a reminder, the Novavax COVID-19 vaccine is a protein-based vaccine. The updated vaccine contains the spike protein from the SARS-Cov-2 virus (Omicron variant XBB.1.5), along with extra ingredients called “adjuvants” that help your body mount a strong immune response. By contrast, mRNA vaccines carry the instructions for your body to make enough of this viral protein for your immune system to recognize it. The updated Novavax vaccine has EUA approval from the US FDA and is expected to be approved soon in Canada.

The best way to get a sense of what to expect in terms of side effects is by looking at the results of clinical trials. This data-driven approach is far more objective than talking to your friends, though maybe not as fun! In short, these trials tell us that the chances of side effects are high with all COVID vaccines, but not quite as high for Novavax compared to mRNA vaccines. Across vaccines, the vast majority of side effects are mild to moderate and short-lived (1-3 days).

Here are some highlights from vaccine trials that included thousands of people:

➡️ Local side effects (like pain at injection site, redness, swelling). Across COVID vaccines, roughly 80-90% of adults (age 18-64) experienced some sort of local reaction after the second dose (numbers were somewhat lower after the first dose). Novavax was on the low end of this range, while the two mRNA vaccines (Moderna and Pfizer/BioNTech) were on the high end. Pain at injection site (mild to moderate) was the most common side effect across COVID vaccines. It was reported by roughly 80% of people who got Novavax or Pfizer, and 90% of people who got the Moderna shot.

➡️ Systemic side effects (like fatigue, fever, and headaches). Novavax had the lowest reported rate of systemic reactions at roughly 72% (age 18-64) for the second dose (numbers were somewhat lower after the first dose). In the same age range, Moderna and Pfizer reported 82% and 83% respectively. The most common side effect for all vaccines was fatigue, with rates ranging from 58% for Novavax (age 18-64, dose 2) to 82% or 83% for Moderna and Pfizer respectively after the second dose. Notably, the placebo group also had their fair share of fatigue (roughly 25% across all vaccines), which reminds us that we can’t be sure that the shot is fully responsible for the way we feel.

➡️ Serious adverse reactions. All COVID vaccines come with a small risk of serious vaccine reactions, and there is no evidence that this risk is lower for Novavax than other vaccines. Serious adverse events for all vaccines are continually monitored through government vaccine surveillance programs. Our most recent estimates suggest that the average risk of severe allergic reactions (anaphylaxis) is about 1 in 100,000, and the average risk of myocarditis and/or pericarditis is about 1 in 50,000 to 1 in 25,000, but ranges considerably by age and sex. It’s natural to worry about these rare but serious reactions – but don’t forget that the health risks that come from being infected with the SARS-CoV-2 virus are far greater.

‼️ Please note: Clinical trials can not perfectly predict what will happen for you – they should only be seen as rough guides. Your unique vaccine response is shaped by many factors including vaccine type, immunity, and age (for example, older adults tend to have fewer side effects). These numbers also have a few important limitations. First, data on side effects are a bit “noisy” because they are self-reported and subjective – in fact, we often see plenty of side effects in the placebo groups. Second, much of the data on side effects is from trials that took place in 2020 and 2021 when most people were COVID-19 “virgins” – we expect different responses now that most of us have encountered the virus (or a vaccine) more than once. Third, most of our data comes from single vaccine trials in different populations, not from trials that make direct comparisons between vaccines in the same population. That said, there was one small head-to-head vaccine comparison, and it found substantially fewer side effects for Novavax as a second shot after Pfizer, compared to Pfizer followed by mRNA).

⭐The Bottom Line⭐

The Novavax vaccine seems to have a slightly better side effect profile than mRNA vaccines, but it’s not a dramatic difference. No matter which shot you get, plan for a bit of downtime in the next couple of days if possible, and hope for the best!

NB: If you had a severe allergic reaction to an mRNA vaccine, that is a great reason to opt for Novavax.

Stay safe. Stay well.

Those Nerdy Girls


Article on Novavax vs other vaccines (Science magazine)

Vaccine side effect data from clinical trials (CDC):


UK study that compared vaccines head-to-head in 2021(Com-COV2)l

COVID-19 vaccine safety (Health Canada)

COVID vaccines and myocarditis: risks vs benefits. (US National Institutes of Health)

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