Israel will roll out a booster dose of the Pfizer-BioNTech COVID-19 vaccine to older people, citing a drop in protection against severe disease driven by the Delta variant

• Israel will begin offering booster shots of Pfizer's coronavirus vaccine this weekend.
• The vaccine's protection against severe illness waned over time from 97% to 81%, officials said.
• With the rise of the Delta variant, many countries are considering booster doses.
• See more stories on Insider's business page.

Israel will start offering booster doses of the Pfizer-BioNTech coronavirus vaccine to its older citizens on Sunday, as health officials described new data showing a decline in the vaccine's protection against severe disease over time.

A key unknown with the COVID-19 vaccine is how long protection will last. The emergence and spread of the Delta variant has intensified that uncertainty, with the variant showing the ability to partially evade the vaccine's protection.

In response to the latest data, Israel is offering a third dose of the vaccine to its citizens who are 60 and older and at least five months removed from their second shot. Other countries are also considering if and when to roll out booster shots. Israel had already begun offering booster shots to some people with compromised immune systems, such as cancer patients.

There has been a trickle of studies in recent weeks suggesting protection from Pfizer's vaccine starts to wane after several months. Israel's decision was motivated by signals of decreased efficacy, The Wall Street Journal reported.

Read more: Pfizer doubles down on the case for COVID-19 vaccine booster shots

In particular, one Israeli scientist said the country had data showing the vaccine's protection against severe illness among this 60-plus age group dropped from 97% in April to 81% in July. Those results have yet to be published in a peer-reviewed medical journal or posted on a preprint server.

Eric Topol, the director and founder of the Scripps Research Translational Institute, said on Twitter that if these results held up, they would be "the first sign of a significant dropdown of protection against hospitalizations and death for these vaccines."

"I hope all of the data will be shared ASAP as the implications are big," he tweeted.

Israel's findings appear at odds with reports from the UK in June, with one large observational study finding Pfizer's vaccine reduced the risk of hospitalization from the Delta variant by 96%. One difference between the two findings is that Israel's results are specific to an older population.

Pfizer presented more results on Wednesday supporting the company's stance that boosters would be needed six to 12 months after initial vaccination. Laboratory testing by Pfizer showed neutralizing antibodies, a key part of the immune response, significantly declined eight months after the second dose of its vaccine among all age groups.

The New York drugmaking giant also posted new, detailed results from its clinical trial that enrolled more than 40,000 volunteers. Longer-term follow-up showed the vaccine's ability to prevent symptomatic COVID-19 cases, regardless of severity, dipped to 84% starting four months after the second dose, compared with 96% efficacy in the first two months.

The vaccine's overall efficacy against severe disease in that study was 97%, with 30 cases occurring among people who received placebo shots and one case in a person who got the vaccine.

Pfizer's findings have also yet to be published in a peer-reviewed medical journal, and the company said it would submit an application to US regulators in August to begin offering booster shots.