New vaccines for COVID-19 are emerging. One such vaccine is Novavax. Early studies indicate that it may have similar efficacy to the Pfizer and Moderna vaccines but fewer side effects. Further trials and analyses of the initial results are underway to understand its effects better.

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What side effects can the Novavax vaccine cause? Image credit: Mariano Vimos/Vizzor Image/Getty Images.

Medical News Today has contacted over 20 experts for comment on the potential side effects of the Novavax COVID-19 vaccine, Nuvaxovid. As of the time of publication, they have declined to comment until additional peer-reviewed data become available.

On January 31, 2022, Novavax submitted a request to the Food and Drug Administration (FDA) for emergency use authorization for its COVID-19 vaccine candidate.

Over 30 countries, including the United Kingdom, Australia, and Germany, have already approved this vaccine for emergency use.

For more advice on COVID-19 prevention and treatment, visit our coronavirus hub.

Unlike mRNA vaccines, such as Pfizer and Moderna, the Novavax vaccine uses a longer-standing protein-based technology. The flu vaccine and the hepatitis B vaccine, which doctors have administered throughout the U.S. since 1986, use this technology.

The proteins inside the Novavax vaccine mimic COVID-19’s spike protein. They were created in moth cells and then assembled into nanoparticles – small particles made of a few hundred atoms. While they share COVID-19’s molecular structure, they do not replicate or cause COVID-19.

The vaccination involves injecting the nanoparticles into arm muscles alongside a compound extracted from the soapbark tree, which acts as an adjuvant to attract immune cells to the injection site.

A full course of the vaccine requires two doses taken 3 weeks apart.

The results from two large phase 3 trials on Novavax have been published.

One trial in the United States and Mexico included 29,949 participants ages 18 and over who had not previously contracted SARS-CoV-2. On a ratio of 2:1, they received two doses of either the Novavax vaccine or a placebo.

Overall, the researchers found that the Novavax vaccine was 92.6% effective against the Alpha and Beta variants of the virus. They also tracked side effects for 7 days after each dose.

While side effects occurred after the first dose, they were more common after the second dose. Common side effects included:

  • tenderness at the injection site for 73% of participants
  • pain upon and after vaccination for 60% of participants
  • fatigue for 50% of the participants
  • muscle pain for 48% of participants
  • headache for 44% of participants
  • malaise for 39% of participants

Less common side effects after the second dose included:

  • fever for 6% of participants, including severe cases for 0.37%
  • nausea and vomiting for 11% of participants, including severe cases for 0.23%
  • joint pain for 22% of participants, including severe cases for 2.44%

A smaller trial including 15,187 participants in the UK found similar results.

Data so far suggest, that on the whole, the Novavax vaccine may have fewer side effects than both the Pfizer and Moderna vaccines.

After a second dose of the Pfizer vaccine:

  • 66% reported pain
  • 60% fatigue
  • 52% headache
  • 38% muscle pain
  • 22% joint pain
  • 16% fever
  • 2% vomiting.

Meanwhile, after a second dose of the Moderna vaccine:

  • 88% experienced pain
  • 16% fever, including 1.4% severe cases
  • 59% headache
  • 66% fatigue
  • 43% joint pain
  • 19% vomiting.

Like the Novavax vaccine, side effects were more common after the second vaccine dose.

The World Health Organization (WHO) recommends Novavax for:

  • those living with conditions that increase the risk of severe COVID-19, such as cardiovascular disease, respiratory disease, and diabetes
  • people who have contracted COVID-19 in the past
  • people who are breastfeeding and those who are not

The WHO the following not to get the vaccine:

  • people with a history of anaphylaxis to any component inside the vaccine
  • people with symptomatic PCR-confirmed COVID-19 until they have recovered and finished self-isolation
  • people with a body temperature of over 38.5°C until they no longer have a fever
  • people under 18 years old, as research studying its safety and efficacy is still underway.

The WHO also highlights that data on having the vaccine during pregnancy is not yet available. However, as other protein-based vaccines have comparable efficacy in pregnant and non-pregnant people, they say that the Novavax vaccine may be the same.

Therefore, they recommend that pregnant people receive information about the risks of COVID-19 during pregnancy, the potential benefits of vaccination, and safety data limitations so that they can make their own decision. However, they recommend pregnant people get vaccinated in situations where the benefits outweigh the risks.

Any side effects from the vaccine were largely mild to moderate and transient. The phase 3 trial in the U.S. and Mexico, and the U.K did not raise any safety concerns.

According to Prof. Paul Heath, professor of paediatric infectious diseases and director of the Vaccine Institute, St George’s, University of London and St George’s Hospital, London, and chief investigator of the Novavax United Kingdom trial:

“The results are very reassuring and importantly show that this vaccine appears to be safe and effective in populations from a range of communities and demographic groups, and those with a range of underlying comorbidities, now (across both trials) with a total number of participants of more than 45,000.”

“Both the U.K. and the US. and Mexico trials used the same case definitions, and these consistent results, therefore, provide much confidence in the use of this vaccine for the global population. We now await the peer-reviewed publication. We also look forward to the results of the trial’s adolescent arm (12–17 years), which recently completed enrolment,” Prof Heath adds.

According to Dr. Peter English, a retired consultant in communicable disease control, former editor of Vaccines in Practice, and immediate past chair of the BMA Public Health Medicine Committee:

“[t]he vaccine is a much more traditional sort of vaccine than the mRNA and vector vaccines currently in use. The actual spike protein is injected, in the form of nanoparticles, instead of inserting the genetic material enabling our cells to create the spike protein.”

He adds that:

“It remains to be seen whether this will have consequences in terms of real-world effectiveness or safety; but the more different types of vaccine we have, the greater our ability will be to optimize effectiveness and safety in different groups.”

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