BioNTech has said that repeat shots of its COVID-19 vaccine, of which more than a billion doses have now been supplied worldwide, was a better strategy than tailoring the product it developed with Pfizer to new variants.

The German biotech firm said that offering a third dose of its established two-shot vaccine remained the best response to concerns over waning immune protection in the face of the highly contagious Delta variant, as worse strains may emerge.

BioNTech said the more than one billion supply tally as per 21st July was up from 700 million-plus doses it announced in June.

This compares with AstraZeneca saying last month that it and manufacturing partner Serum Institute of India had supplied a billion doses of its vaccine globally.

Based on delivery contracts signed for more than 2.2 billion doses so far, BioNTech said in a statement detailing its second quarter earnings that it expects to accrue 15.9 billion Euros ($18.7 billion) in revenue from the vaccine this year, up from a May forecast of 12.4 billion Euros.

That includes sales, milestone payments and a share of gross profit in its partners’ territories, BioNTech added.

Pfizer late last month raised its forecast for its share of 2021 vaccine sales to $33.5 billion and said at the time it believes people will need a third dose of the shot.

Pfizer and BioNTech’s decision in early July to seek authorisation for a third dose drew criticism from the US health regulators, who said there was not yet enough data to show booster shots are needed.

The US health agencies have since discussed additional doses for people with compromised immune systems, while Germany and France said they would roll out a third dose for the most vulnerable from September.

That jars with a call by the World Health Organization (WHO) to use doses instead to jump-start vaccination campaigns in poorer nations which have so far been left behind.

BioNTech Chief Executive Ugur Sahin said that although work was ongoing to adjust the vaccine to variants, it was not clear whether yet another version of the pathogen would supplant the now-prevalent Delta variant.

“Making a decision at the moment might turn out to be wrong in three or six months if another variant is dominating,” Sahin said during an analyst call.

Oezlem Tuereci, Chief Medical Officer, BioNTech, said that lab experiments had shown that a third shot of the established product generated neutralising antibodies against a range of strains and that the antibody boost was above the one following a second dose.

Still, the company reiterated plans to start testing a vaccine adjusted to the Delta variant on humans this month, part of a “comprehensive strategy to address variants.”