When can we expect a variant specific (i.e. Delta variant) booster shot?


A: Variant specific boosters are currently being tested, but it’s not clear whether we need them just yet.

Here is a run-down of ongoing trials:

Pfizer/BioNTech has two Phase 2/3 trials ongoing, one with a booster designed to target the Beta variant (the one that emerged in South Africa in late 2020) and one that is designed to target the Delta variant (the now dominant variant).

Moderna is also testing boosters targeted against just Beta, just Delta, BOTH Beta and Delta, and one that targets the original SARS-CoV-2 virus as well as the Beta variant in Phase 2/3 trials. Interim findings showed that ALL boosters increased neutralizing antibodies against the original SARS-CoV-2 virus as well as the Beta and Delta variants to levels that were equal to or greater than that observed 1 month after the original vaccine series. This trial is ongoing.

AstraZeneca is also carrying out Phase 2/3 trials testing a Beta variant-specific booster in those who were previously vaccinated (with the AstraZeneca vaccine or a mRNA vaccine) as well as unvaccinated adults. Unvaccinated adults will receive 2 doses of the Beta variant specific vaccine either 4 or 12 weeks apart or one dose of the original AstraZeneca vaccine and a second dose of the Beta variant specific vaccine 4 weeks later.

Results from all these trials are expected later this year.

But are variant specific boosters even necessary?

Across the board, antibody responses triggered by additional doses of the *original* vaccine formulations for currently approved COVID-19 vaccines have been reported to be very robust-including against the Delta variant. For this reason, booster doses of the original vaccines may be sufficient and variant specific boosters may not be needed.

Indeed, a booster dose of the original Pfizer vaccine was already approved by the Food and Drug Administration (FDA) in the U.S. for certain groups (see our post on this here.).

The FDA is also meeting on Oct 14th to talk about booster shots for those who received the Moderna or J&J vaccines, so we should have more information on booster recommendations for people who received these vaccines soon.

There is also the potential for a mix-and-match booster strategy to be approved in which people get a booster with the original formulation of a vaccine other than the one they initially received. In the UK, the Joint Committee on Vaccinations and Immunizations recently approved booster shots for adults aged 50+ who are 6 months past their 2nd dose as well as vulnerable younger populations (original formulation of the Pfizer vaccine or ½ dose of the Moderna vaccine recommended) regardless of original vaccine received. For more info on this, see our previous post.

The FDA will be discussing the results from ongoing “mix-and-match” trials on October 15th-and if a mix-and-match strategy is approved, this would further expand our booster options.

Until we see trial results for variant specific boosters, it is hard to say whether they will prove to provide better protection than boosters of the original vaccine formulations or a mix-and-match strategy. It is possible that variant specific boosters will become another tool in our toolbox, but we just don’t know yet. In general, if you are eligible for a booster vaccine now, it doesn’t make sense to hold out for a variant specific vaccine at this point.

Keep tuning back in and Those Nerdy Girls will keep pushing out updates as we hear more.

For Moderna variant specific booster trial interim results, see here.

For our previous post on J & J vaccine and preliminary findings regarding boosters, see here.

For more information on what a mix-and-match strategy is, see here  or here.

For our most recent Facebook Live ALL about boosters, see here.

For further reading on whether there is a need for variant specific boosters, see here  or here.

Link to Original FB Post