Eyeing delta surge, Pfizer will file COVID-19 booster next month

With the COVID-19 delta variant becoming the dominant strain circulating in the US, Pfizer and BioNTech have said they will ask the FDA and other regulators to approve a third dose of their Comirnaty vaccine to guard against a winter surge in cases.

The two companies have revealed data from an ongoing trial of the booster Comirnaty (BNT162b2) jab, saying that a dose given six months after the second dose stimulates a strong antibody response against both the original wild type and the worrisome beta strain of SARS-CoV-2.

The antibody responses after a booster "are five to 10 times higher than after two primary doses," they said, adding the plan is to file for approvals in the US and Europe for a third dose in the coming weeks.

Meanwhile, sera taken from patients after a second dose show that antibodies generated by the vaccine have a strong neutralising effect on the delta variant in lab tests, according to Pfizer, although an Israeli study reported a decline in efficacy for the shot against delta earlier this week.

The results are encouraging as beta has been shown to be the most likely of the variants identified to date to evade the immune response generated by COVID-19 vaccines, while delta is more transmissible and – according to federal data – accounted for almost 52% of all COVID-19 infections in the two weeks to 3 July.

Delta is also more likely to cause severe disease in the unvaccinated, which is a concern as some areas of the US are experiencing vaccine hesitancy and a slowdown in vaccination rollout.

"As seen in real world data released from the Israel Ministry of Health, vaccine efficacy in preventing both infection and symptomatic disease has declined six months post-vaccination, although efficacy in preventing serious illnesses remains high," said the companies in a statement.

"We continue to believe that it is likely, based on the totality of the data we have to date, that a third dose may be needed within six to 12 months after full vaccination," they added.

Pfizer and BioNTech have said they are already working on an updated version of Comirnaty that targets the full spike protein of the delta variant, with a first batch now manufactured and due to start clinical testing next month, subject to regulatory approvals.

The updated version may not be needed however, if the two companies' hypothesis that the current version of Comirnaty produces effective antibodies against the variant proves correct. That is backed up by a Public Health England study reported in May which suggested that the Pfizer/BioNTech shot provided 88% protection against the delta variant after two doses.