New research published in JAMA Internal Medicine is offering the best insight to date into the long-term benefit of a third COVID-19 vaccine dose. Tracking over 300,000 subjects in Israel the research shows a third dose of Pfizer’s mRNA vaccine reduces a person’s chance of SARS-CoV-2 infection by 86 percent compared to two doses.
In light of the emergence of yet another concerning SARS-CoV-2 variant many countries around the world have started rolling out broad third-dose COVID-19 vaccine programs. Despite COVID-19 vaccines showing robust long-term protection from severe disease, hospitalization and death, protection from infection or mild illness has been seen to wane around five or six months following a second dose.
On the first of August this year Israel became the first country in the world to begin a national third-dose vaccination campaign, making it a perfect test case for studying the lasting effects of a third COVID-19 vaccine dose.
The new study compared positive COVID-19 cases between those who received two doses of Pfizer’s mRNA vaccine and those who received three doses. The data included more than 300,000 people over the age of 40 and covered a period of time up to early October.
The research found around two weeks after a third dose, rates of COVID-19 infection significantly dropped compared to what was seen in a matched two-dose cohort. Relatively, those receiving three vaccine doses were 86 percent less likely to report a positive infection, and this protection was consistent for the entire 65-day follow-up period in the study.
“These numbers should be interpreted as the reduction in the odds of infection in a person receiving the booster dose compared with a person receiving only the two primary doses,” the researchers stress in the study. “This reduction comes on top of the reduction in the risk conferred by the first two doses.”
The findings recall another recent real-world investigation into the effectiveness of third vaccine doses out of the United Kingdom. That research concluded a third dose provides 80 percent greater protection from symptomatic COVID-19 compared to two doses.
However, the UK research only offered insight into protection two weeks after a third vaccine dose. This new data out of Israel provides a valuable glimpse at how long that third dose protection could last by providing infection data more than two months beyond the booster shot.
Perhaps the key question yet to be answered is how long does third dose protection last? Will it decline at the same rate seen after two doses or will a third dose hold strong for a longer period of time?
Israel’s health minister recently suggested a fourth vaccine dose may be necessary if the country experiences a new wave of infections. But some preliminary research has indicated protection after a third dose may be more robust than what was seen after two doses. And, of course, none of these projections take into account the recent emergence of the Omicron variant.
The new study was published in the journal JAMA Internal Medicine.
