A: If booster shots or vaccines adapted to new variants of the SARS-CoV-2 virus become necessary, it is likely they will be able to be used by those originally vaccinated with a different type of vaccine. This strategy might even have added benefits!
While it is currently not recommended that we mix and match COVID-19 vaccine types until more data on this approach is available, it is likely that the immune response may actually be enhanced with this strategy via something known as a, “heterologous prime-boost”. This is a phenomenon whereby different vaccines stimulate an immune response in slightly different ways, creating a more robust immune response overall (pretty cool, right?). Indeed, studies in mice have already shown that a combination of an RNA coronavirus vaccine and the AstraZeneca vaccine stimulated better CD8+ T cell responses than either vaccine alone. See link to our previous post on this (including some caveats) below!
To better understand how this works in humans, a trial is currently ongoing in the UK in which individuals are receiving various combinations of the Pfizer and AstraZeneca vaccines with data expected to be available as soon as June. Moderna has also stated that the booster doses currently being tested by their company will be able to be used among those previously vaccinated with the Moderna vaccine, who received another available vaccine or who were infected with the original SARS-CoV-2 virus. Overall, it may end up that a mix and match strategy for booster vaccines is not only approved, but preferred. Stay tuned for more information on this as it becomes available!
The good news is that regardless of whether it is determined that the same or a different vaccine is best, several strategies are currently being tested for boosting vaccine protection against new variants, so we should have several options either way!
First, almost all companies are testing (or plan to test) whether administering an *additional dose* of the original vaccine an individual received, improves protection against variants by increasing the level of antibodies targeted against the spike protein that are produced. For example, Pfizer is currently testing administration of a booster dose 6-12 months after the first dose in a subset of individuals who participated in the original Phase 1 trial.
Second, some companies are currently testing *new formulations* of the vaccine that specifically target mutations contained in a given variant. In fact, Moderna shipped their newly formulated vaccine (targeted to the B.1.351 variant) to the United States National Institutes of Health on February 24th to begin a new Phase 1 trial!
Third, companies may develop and test a *bi- or multi-valent vaccine* which targets the spike protein on the original SARS-CoV-2 virus as well as that on one or more new variants, in a single vaccine. Novavax, for example, announced in January that they have begun this process.
The other good news is that while studies have identified that available vaccines have lower efficacy against some new variants (B.1.351 in particular), efficacy wasn’t zero. Vaccines prompt the body to produce antibodies that target various regions of the spike protein on the SARS-CoV-2 virus. For this reason, even if mutations on the spike protein occur, it is unlikely that currently available vaccines will be completely ineffective against new variants. Also, all of the currently available vaccines were shown to be highly effective at preventing hospitalization and death-even those tested during periods or in geographic regions where certain variants were more dominant. So when it is your turn, don’t hesitate to get vaccinated with one of the currently available vaccines. *The best vaccine is the one you can get today!*
Overall, since it will take several months before booster vaccines are available, our best bet is to continue to use all our SMARTS (Space, Mask, Air, Restrict, Time and SHOTS) as the more we can continue to slow down transmission, the fewer chances there are for mutations in the virus to develop. Stay safe, stay sane!
Our previous posts on new variants:
Other recent articles on strategies to deal with variants: