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How will scientists decide when to update vaccines in response to new SARS-CoV-2 variants?

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SciLine tracks common science questions that reporters have about the coronavirus pandemic – and reaches out to our network of scientific experts for quotable comments in response. Reporters can use the comments below in news stories, with attribution to the scientist who made them.

This article was published on
February 3, 2021

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Expert Comments: 

Dave O’Connor, PhD

Scientists can draw blood from people who have received the vaccine and extract the serum (liquid) part of the blood that contains antibodies. They can then ask how well those antibodies work to prevent the virus from infecting cells in the lab. The good news, for the moment, is that the antibody responses to the virus by vaccinated people are strong. This means that even a 2-fold or 5-fold reduction in antibody recognition due to a particular variant would still be expected to be protective. As new variants of concern arise and spread, they can be tested in the lab against the blood of vaccine recipients using the same types of tests to determine the new variant’s susceptibility to vaccine-induced antibodies. There are efforts underway to create standardized ‘panels’ of antibodies from diverse groups of vaccine recipients so these experiments can be done by researchers from around the world against whatever viruses emerge in their own neighborhoods. The standard scientist caveat of ‘we need more data’ is true here too. Since we only have two months of ‘real world’ vaccine effectiveness data, and very limited data against the variants, these lab-based predictions will need to be validated in the real-world and could be wrong.

Jiang Zhu, PhD

Updating vaccines for each emerging new strain is not practical. Since all first-generation vaccines are based on the spike gene of the ancestral strain from Wuhan, perhaps the first step should be testing serum antibodies in animals and humans immunized with these vaccines against the new variants. If a there is a significant (e.g., more than 50%) reduction in the ability of antibodies found in the blood of vaccinated people and animals to neutralize the virus, an update may be considered. However, it is unclear what the right threshold should be for such evaluation. A more stringent test would be a virus challenge in live animals susceptible to SARS-CoV-2 infection. If current vaccines fail to confer protection against new variants, they must be updated.

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