Vaccination with two doses of the Pfizer jab stays highly effective against severe Covid — including the Delta variant — for at least six months, an analysis of US patients said Monday.
While previous data from clinical trials has shown jabs protect against hospitalisation, the study published in the Lancet measures one vaccine’s effectiveness over time in a real-world setting.
Pfizer and healthcare provider Kaiser Permanente looked at records from 3.4 million residents of southern California, about a third of whom were fully vaccinated between December 2020 and August 2021.
After an average period of three to four months, fully vaccinated people
were found to be 73 percent protected against infection and 90 percent
protected against hospitalisation.
But while protection against infection from Delta fell by 40 percent over
five months, protection against hospitalisation involving cases from all
variants remained very high for the duration of the study.
The results, the study notes, are consistent with preliminary data from US
and Israeli health authorities.
Reduced infection defence is “likely to be primarily due to waning vaccine
effectiveness rather than the delta variant escaping vaccine protection”, the
“Our findings underscore the importance of monitoring vaccine effectiveness
over time and suggest that booster doses are likely to be needed to restore
the initial high amounts of protection observed early in the vaccination
programme,” it says.
In August the US authorised an extra dose of Covid-19 vaccine for people
with weakened immune systems, while in France an extra shot has been offered
to the elderly.
Israel has gone further, offering children 12 and older a third dose five
months after receiving a second jab.
A September report, however, from the World Health Organization (WHO) found
current vaccines are effective enough against severe Covid to make a third
jab unnecessary for the general population.
The WHO last month called for a moratorium on booster jabs until the end of
the year to address the drastic inequity in dose distribution between rich
and poor nations.