Dolsten said Pfizer interprets the Israeli finding as a sign that blood-antibody levels have faded somewhat since people in Israel started being vaccinated in January and February. In the presence of a highly transmissible strain, that may allow mild cases to slip through even though people remain protected against severe disease, he said.
Even when front-line antibodies have faded slightly, the vaccine still produces a variety of memory responses that can stave off serious illness, Dolsten said.
“When you have low blood levels of an antibody, viruses that are highly contagious may reinfect and cause mild disease,” Dolsten said.
Separately, Pfizer plans to begin human trials of a new booster customized against the delta strain. But Dolsten said it was unlikely that this customized vaccine would be needed, as the existing vaccine does a good job of producing antibodies against the variant.
Even preventing mild cases can be useful because it will help slow infections that can lead to new variants, and will prevent cases of long Covid that can occur even after mild infections, Dolsten said.
In the past, Pfizer Chief Executive Officer Albert Bourla has suggested that Covid booster shots might be needed for most people within 12 months, and annual boosters might be necessary after that. But medical experts have cautioned that it isn’t clear whether and when boosters will be needed.
With only a small portion of the world vaccinated so far and variants emerging like wildfire, booster shots may be an important way to keep vaccinated parts of the world from having to continually going back to disruptive social distancing measures, Dolsten said.
“For the next few years, it is better to be prepared for what seems like a sober reality than to hold for miracles,” he said.
The Pfizer shot is one of the leading Covid vaccines globally. As of July 1, Pfizer said it had shipped more than 860 million doses of its vaccine around the world, including over 330 million doses to the EU and over 200 million doses to the U.S.
In the U.S., over 184 million doses of the Pfizer vaccine have been administered so far, outpacing 135 million doses of Moderna Inc.’s vaccine that have been used in the country, according to the Centers for Disease Control and Prevention.
This article was provided by Bloomberg News.