According to a new study published Monday in the Lancet, the effectiveness of Pfizer/BioNTech vaccine in preventing COVID-19 infection declined to 47% from 88% six months following the second dose. The U.S. health agencies had considered the data when deciding on the need for a booster dose.

The study revealed that the vaccine′s effectiveness in preventing hospitalization and death continued to be high at 90% for at least six months, even against the Delta variant. Researchers evaluated electronic health records of around 3.4 million individuals who were members of Kaiser Permanente Southern California, between December last year and August of this year. Luis Jodar, senior vice president and chief medical officer at Pfizer vaccines, said that the variant-specific analysis demonstrated that the vaccine was effective against all variants of concern, including the Delta variant. The vaccine’s effectiveness against Delta was 93% after the first month, and came down to 53% after four months. Against other variants, the efficacy dropped from 97% to 67%... (Reuters, October 5, 2021)