February 15
THE efficacy of third doses of the Pfizer and Moderna mRNA vaccines wanes substantially by the fourth month after administration, a new study by the US Centres of Disease Control and Prevention (CDC) said on Friday.
Though it’s now well documented that vaccine efficacy goes down after two doses, relatively little has been published on the duration of protection after a booster.
“COVID-19 vaccine boosters remain safe and continue to be highly effective against severe disease over time,’’ said Kristen Nordlund, a CDC spokesperson.
More than 241,204 visits
The new study was based on more than 241,204 visits to the emergency department or an urgent care clinic, and 93,408 hospitalizations, which are more serious, among adults with COVID-19-like illness during 26 August 2021-22 January 2022.
Vaccine efficacy was esti mated by comparing the odds of a positive COVID test between vaccinated and unvaccinated patients and using statistical methods to control for calendar week, geographic area, while adjusting for age, the level of local transmission, and patient characteristics like comorbidities.
During the Omicron-predominant period, vaccine efficacy against COVID-associated emergency department or urgent care visits was 87 per cent during the two months after a third dose, but fell to 66 per cent by the fourth month.
Vaccine efficacy against hospitalization was 91 per cent in the first two months, but fell to 78 per cent by the fourth month after a third dose.
“COVID-19 vaccine boosters remain safe and continue to be highly effective against severe disease over time,’’ said Kristen Nordlund, a CDC spokesperson.
“The finding that protection conferred by mRNA vaccines waned in the months after receipt of a third vaccine dose reinforces the importance of further consideration of additional doses to sustain or improve protection,” the authors concluded.
Speaking at a White House COVID briefing on Wednesday, President Joe Biden’s top medical advisor Anthony Fauci said it was likely that fourth doses would more likely be needed for subsets of people who mount weaker immune responses, such as the elderly and immunocompromised.
Effectiveness after a booster
Effectiveness after a booster was higher last year, when the delta variant was causing most US cases, the study noted.
Health experts expect protection from the vaccines to wane. The US booster campaign was based on evidence that emerged last year that vaccine protection was fading six months after people got their initial vaccinations.
And from the beginning, vac cines have offered less protection against the omicron mutant than earlier versions of the virus. The study couldn’t address how protection will hold up against the next variant to come along.
Still, the new study’s finding was notable, said Dr. William Schaffner, a Vanderbilt University vaccines expert.
“I’m a little surprised, according to the data, that it’s starting to wane already,” he said, adding that he would have anticipated higher estimates of vaccine effectiveness at the four-month post-booster mark.
But Schaffner also said he’d like to see more research about the durability of booster protection, adding “let’s take this with a grain of salt.’’
Dr Michael Saag, an infectious diseases physician at the University of Alabama at Birmingham, said 78 per cent effectiveness against hospitalisation “is still pretty effective.”
“Anecdotally, I’m seeing very few people die who got boosted,” he said, even among those with weakened immune systems. “The vaccines are still working.’’
New antibody authorized
In a separate development on Friday, the Food and Drug Administration (FDA) authorised a new lab-grown antibody treatment by pharmaceutical company Lilly called bebtelovimab.
The drug is administered as an intravenous injection over at least 30 seconds and has been green lighted for the treatment of mild-to-moderate COVID among people 12 and over at high risk of severe disease. Data supporting the authorization came from a clinical trial that showed the drug has strong promise against Omicron. Lilly’s previous antibody treatment was de-authorized by the FDA after it was found to be ineffective against this variant. SOURCE: AFP
