Pfizer plans to ask US regulators to authorize a booster dose of its COVID-19 vaccine within the next month, the drugmaker's top scientist said on Thursday, according to Reuters.

The move is based on evidence of greater risk of reinfection six months after inoculation and due to the spread of the highly contagious Delta variant.

Pfizer Chief Scientific Officer Mikael Dolsten said the recently reported dip in the vaccine's effectiveness in Israel was mostly due to infections in people who had been vaccinated in January or February.

"The Pfizer vaccine is highly active against the Delta variant," Dolsten said in an interview, according to Reuters. But after six months, he said, "there likely is the risk of reinfection as antibodies, as predicted, wane."

He stressed that data from Israel and Britain suggests that even with waning antibody levels, the vaccine remains around 95% effective against severe disease.

Dolsten said that early data from the company's own studies shows that a third booster dose generates antibody levels that are five to 10-fold higher than after the second dose, suggesting that a third dose will offer promising protection.

Pfizer is already targeting production of 3 billion doses this year and 4 billion doses next year. Dolsten declined to give a forecast of exactly how many more doses the company could add, but said "we can step up billion after billion in '22."

Earlier this week, it was reported that the Israeli Health Ministry is planning to issue a recommendation for a third dose of coronavirus vaccine for people with underlying illnesses or weaknesses that render them more vulnerable to serious illness.

The first to receive a third dose will be those with heart issues and transplant patients, according to the report, followed later by those with other health issues.

Just last week, opposition leader Benjamin Netanyahu called on Health Minister Nitzan Horowitz to make the necessary preparations for a third vaccine dose for the entire population, explaining that no one knows how long the immunity provided by the vaccines will last.