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Are vaccinated individuals more likely to be infected with and transmit virus variants?

This article was published on
April 23, 2021

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There is currently no research to suggest that vaccinated people would be more likely than their unvaccinated counterparts to transmit variants of SARS-CoV-2. The U.S. Centers for Disease Control and Prevention (CDC) has stated that "a growing body of evidence suggests that fully vaccinated people are less likely to have asymptomatic infection and potentially less likely to transmit SARS-CoV-2 to others." The U.S. CDC also says there is evidence that the currently authorized COVID-19 vaccines provide at least some level of protection against variants of concern, including B.1.1.7 originally identified in the U.K. and B.1.351 originally identified in South Africa. The World Health Organization (WHO) recommends widespread vaccinations to potentially help reduce the transmission of current variants, as well as prevent the emergence of new variants. More research is being conducted to learn more.

There is currently no research to suggest that vaccinated people would be more likely than their unvaccinated counterparts to transmit variants of SARS-CoV-2. The U.S. Centers for Disease Control and Prevention (CDC) has stated that "a growing body of evidence suggests that fully vaccinated people are less likely to have asymptomatic infection and potentially less likely to transmit SARS-CoV-2 to others." The U.S. CDC also says there is evidence that the currently authorized COVID-19 vaccines provide at least some level of protection against variants of concern, including B.1.1.7 originally identified in the U.K. and B.1.351 originally identified in South Africa. The World Health Organization (WHO) recommends widespread vaccinations to potentially help reduce the transmission of current variants, as well as prevent the emergence of new variants. More research is being conducted to learn more.

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What our experts say

Early research supports vaccines as an important tool for reducing the transmission of SARS-CoV-2 variants. Research suggests that current COVID-19 vaccines are at least partially effective against variants of concern. A study published in March 2021 in the peer-reviewed Journal of the American Medical Association (JAMA) indicated that vaccines may work against the B.1.1.7 variant that originated in the U.K.

Despite the growing challenges with variants of concern, the World Health Organization (WHO) continues to recommend vaccinations as a tool to potentially reduce the transmission of current variants and help prevent the emergence of new variants. The WHO says increasing vaccinations and reducing the amount of viral transmission can potentially also help with "reducing opportunities for the virus to mutate."

A higher viral load (the amount of virus measured in the body) has been identified in several studies as a driver for transmission, and research suggests that vaccinated people may have a lower viral load compared to unvaccinated individuals who become infected. Preliminary data from Israel, a country which has vaccinated a large proportion of citizens against COVID-19, suggests that infected vaccinated individuals may have a four-fold lower viral load, compared to infected unvaccinated individuals. This finding supports vaccination as a way to reduce the spread of COVID-19.

Context and background

Clinical trials for COVID-19 vaccines also demonstrated reduced likelihood of severe disease when infected and reduced likelihood of asymptomatic infection. Reducing asymptomatic infections through vaccinations can help reduce the chances of someone unknowingly transmitting the disease to others.

Moderna clinical trials looked at study participants who had received a first dose and tested positive for COVID-19 at their second dose appointment. Researchers found that the number of asymptomatic infections was two-thirds lower among those who received the vaccine, compared to those who received the placebo. This was further supported by a study of mRNA vaccines in real-world conditions, where results demonstrated that the Pfizer and Moderna vaccines reduced both symptomatic and asymptomatic transmission. 

Resources

  1. Science Brief: Background Rationale and Evidence for Public Health Recommendations for Fully Vaccinated People (U.S. Centers for Disease Control and Prevention)
  2. Interim guidance on the benefits of full vaccination against COVID-19 for transmission and implications for non-pharmaceutical interventions (European Centre for Disease Prevention and Control)
  3. Neutralizing Antibodies Against SARS-CoV-2 Variants After Infection and Vaccination (Journal of the American Medical Association)
  4. Decreased SARS-CoV-2 viral load following vaccination (Preprint in medRxiv)
  5. Transmission of COVID-19 in 282 clusters in Catalonia, Spain: a cohort study (The Lancet)
  6. Peer-reviewed report on Moderna COVID-19 vaccine publishes (U.S. National Institutes of Health)
  7. Efficacy and Safety of the mRNA-1273 SARS-CoV-2 Vaccine (New England Journal of Medicine)
  8. CDC Real-World Study Confirms Protective Benefits of mRNA COVID-19 Vaccines (U.S. Centers for Disease Control and Prevention)
  9. COVID-19 Vaccines vs Variants—Determining How Much Immunity Is Enough (Journal of the American Medical Association)
  10. The effects of virus variants on COVID-19 vaccines (World Health Organization)

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