All viruses change over time. These changes are called “mutations.” A virus with one or more new mutations is called a “variant” of the original virus. Most viral mutations have little to no impact on the virus’ ability to cause disease. But depending on where the changes are located in the virus’s genetic material, they may affect a virus’ properties, such as transmission (it may spread more or less easily) or severity (it may cause more severe disease). Since the COVID-19 outbreak began, the virus that causes the disease (SARS-CoV-2) has changed to create “variants.” Currently, there are eight variants. Vaccines differ in their effectiveness against variants.


The alpha variant was first identified in the United Kingdom in September 2020. The alpha variant is 30-40% more transmissible than the original virus. Vaccination against the alpha variant is 75% effective with the AstraZeneca vaccine, 94% with the Pfizer vaccine, 86% with the Novavax vaccine, and 100% with the Moderna vaccine.


The beta variant was first seen in South Africa in May 2020 and has a 50% increase in transmission. Both Pfizer and Moderna say that their vaccines are still 95% effective against the beta variant, including against severe disease and death. Novavax (60%) and Johnson &Johnson (57%) seem to be less effective against beta. Recent data indicate that the AstraZeneca vaccine is 82% effective in preventing severe disease and death from COVID after a single vaccine dose.


The gamma variant was first identified in Brazil in November 2020 and is concerning. It remains the dominant variant in South America. Research suggests that gamma is up to 2.4 times more transmissible than the original virus. Few studies have been conducted to determine vaccine efficacy against the gamma variant.


The delta variant is now dominant in Europe and the U.S. and continues to cause new cases throughout much of Asia as well as in India, where it was first identified in October 2020. Delta is the most transmissible form of COVID detected so far. The data are hopeful regarding existing vaccines: research suggests vaccine effectiveness of 67% with the AstraZeneca vaccine and 88% with Pfizer against the delta variant.

More variants are appearing

Other variants include eta, iota, kappa and lamda. Although these have appeared in many countries, little is known about them including how effective vaccines are against them. Ensuring equitable access to COVID-19 vaccines is more critical than ever. As more people get vaccinated, the fewer virus mutations.


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