Vaccination with two doses of the Pfizer jab remains highly effective against severe COVID-19 — including the delta version — for at least six months, an analysis of US patients said on Monday.
While previous data from clinical trials has shown jabs to protect against hospitalization, the study published in The Lancet measures the effectiveness of a vaccine over time in a real-world setting.
Pfizer and healthcare provider Kaiser Permanente looked at the records of 3.4 million residents of Southern California, about a third of whom were fully vaccinated between December 2020 and August 2021.
After an average duration of three to four months, those who were fully vaccinated were found to be 73 percent protected from infection and 90 percent from hospitalization.
But protection against infection from Delta dropped by 40 percent over five months, but protection from hospitalization remained high for all types of cases for the study period.
The results, the study notes, are in line with preliminary data from US and Israeli health officials.
The reduced infection defense “is likely due primarily to reduced vaccine effectiveness rather than a delta variant escaping vaccine protection”, the authors conclude.
“Our findings underscore the importance of monitoring vaccine effectiveness over time and suggest that booster doses are likely to be needed to restore protection at the initial high doses in the vaccination program,” it says.
In August the US authorized an additional dose of the COVID-19 vaccine for people with weakened immune systems, while France has offered an additional shot to the elderly.
Israel has gone ahead, offering children 12 years of age and older a third dose five months after receiving the second jab.
However, a September report by the World Health Organization (WHO) found that existing vaccines are effective enough to make a third jab unnecessary for the general population against severe COVID-19.
The WHO last month called for a halt to booster jabs by the end of the year to address the huge disparity in dose distribution between rich and poor countries.
(Except for the title, this story has not been edited by NB staff and is published from a syndicated feed.)