COVID vaccines being used in Australia are still effective, especially against hospitalisation and death, but less so since new variants came through, according to US research.
In a study published last week in The New England Journal of Medicine, the team of US clinicians compared COVID outcomes in almost 1.8 million people across the US, about 12% of whom had been boosted or vaccinated with one of the newer vaccines targeting subvariant XBB.1.5 (the vaccines currently preferred in Australia.)
Specifically, 218,250 persons (11.9%) received XBB.1.5 vaccines, of whom 133,403 (61.1%) received the Pfizer–BioNTech vaccine and 84,307 (38.6%) received the Moderna vaccine. A total of 21,988 SARS-CoV-2 infections, 1,364 COVID–related hospitalizations, and 237 COVID-related deaths were reported.
Compared with the general population, which includes unvaccinated people and people vaccinated with earlier versions of the vaccines, the researchers calculated the XBB.1.5 vaccines were 52.2% effective against symptomatic infection after four weeks, down to 32.6% and 20.4% at 10 and 20 weeks respectively.
Effectiveness against hospitalisation at four and 10 weeks was 66.8% and 57.1%, respectively, and while its effectiveness against death was higher, it was also less certain because there were very few deaths.
The team also noted that over the course of the study the effectiveness of vaccine appeared to reduce somewhat as newer, non XBB.1.5 variants began to spread.
“During the study period, the dominant circulating variants changed from EG.5 and XBB.1.16 to HV.1 and then to JN.1, and the prevalence of the XBB.1.5 subvariant decreased from 10% to less than 1%,” Dr Patrick Maloney, from the University of Nebraska said.
“We also analysed the data separately for two vaccination cohorts: persons who received the XBB.1.5 vaccines on or before October 25, 2023, and those who received them after October 25, 2023. Each cohort had approximately the same number of XBB.1.5 vaccine recipients.
“The vaccine effectiveness was lower in the second cohort than in the first, which indicates that the XBB.1.5 vaccines were less protective against JN.1 than against XBB sub-lineages.”
The vaccine effectiveness against infection reached a level of 52.2% after four weeks. It decreased to 32.6% (95% CI, 28.1 to 36.8) after 10 weeks and to 20.4% (95% CI, 6.2 to 32.5) after 20 weeks.
The effectiveness against hospitalisation reached a level of 66.8% after four weeks and decreased to 57.1% after 10 weeks.
Additional analyses showed that the XBB.1.5 vaccines were effective across age groups and in persons who had not been previously infected or previously vaccinated, when considering four clinical end points: infection, hospitalization, hospitalization, or death (whichever occurred first), and death.