Finally, Real-World Effectiveness Data on Pfizer Boosters Across Ages

A booster dose of Pfizer vaccine (Comirnaty) dramatically reduced the rate of both infection and severe disease across age groups, beginning at age 16, real-world data from Israel found.

Confirmed infection in individuals who received a booster was lower by a factor of about 10, while severe illness was lower by a factor of about 18 among those ages 60 and up, and by a factor of about 22 among those ages 40 to 59, reported Yair Goldberg, PhD, of Technion-Israel Institute of Technology in Haifa, and colleagues.

Per 100,000 person-days, the adjusted rate differences amounted to 57.0 to 89.5 fewer infections for the booster groups (across age groups), and 5.4 fewer severe cases among those ages 60 and up and 0.6 fewer severe cases among those ages 40 to 59, they wrote in the New England Journal of Medicine (NEJM).

Notably, the adjusted rate difference in deaths was 2.1 per 100,000 person-days in the primary analysis, with the rate of COVID-associated death lower in the booster group among people ages 60 and up by a factor of about 15, they noted.

Since August 29, Israel has recommended a booster dose of Pfizer vaccine for individuals as young as age 12. The U.S. currently recommends boosters for all those ages 18 and up.

Goldberg's group noted that while prior data found boosters were protective against severe disease in older adults, "the extent of protection in younger age groups requires further clarification."

They examined data from the Israel Ministry of Health database from July 30 to October 10 for about 5 million individuals who received the two-dose series of Pfizer vaccine. Those who received the booster at least 12 days earlier were the booster group (104 million person-days) and those who had not were the non-booster group (98 million person-days).

Overall, there were 6,160 confirmed infections, 175 cases of severe illness, and 35 deaths in the booster group, as well as 83,481 confirmed infections, 1,171 cases of severe illness, and 298 deaths in the non-booster group.

Goldberg's group noted the rate of confirmed infection was similarly lower across age groups when comparing the booster group to the non-booster group, with a range across groups from a factor of 9.0 (among ages 30-39) to 17.2 (among ages 16-29) lower.

They added that the rate of severe disease in these younger age groups was 26 cases in the non-booster group and one in the booster group, and not enough "to estimate the rate ratio reliably."

Limitations to the data included unmeasured confounders, which could bias the results. Goldberg's group also added that this analysis calculated "a spatial-temporal index of risk according to the number of infections in each area of residence" to measure exposure risk rather than using calendar dates.

Pfizer Booster Lowers Mortality Rate in Older Adults

A second NEJM study also examined real-world data from Israel. Ronen Arbel, PhD, of Clalit Health Services, and colleagues, found that adults ages 50 and up who received a booster at least 5 months after their two-dose Pfizer primary series had 90% lower mortality rate compared to those who did not receive boosters (adjusted HR 0.10, 95% CI 0.07-0.14, P<0.001).

They examined data from Clalit Health Services electronic health records for adults ages 50 and up from August 6 (a week after boosters were approved for those ages 60 and up) to September 29.

Overall, 843,208 adults were included in the analysis, and Arbel's group noted that by the end of the study, 90% of this population had received a booster dose. Mean age was about 69, and 60% of adults were ages 65 and up. About 46% had hypertension, 33% had obesity, and 29% had diabetes.

There were 65 deaths in the booster group (0.16 per 100,000 people per day) and 137 in the non-booster group (2.98 per 100,000 per day).

Interestingly, "socioeconomic status, diabetes, chronic obstructive pulmonary disease, ischemic heart disease, chronic heart failure, obesity, history of transient ischemic attack, and history of smoking did not have a significant association with death" due to COVID, Arbel's group wrote.

Primary Vaccinations Still a Global Priority

In an accompanying editorial, Minal Patel, MD, of the CDC in Atlanta, noted that boosters are being provided to some or all of the eligible population in 107 countries as of November 23, but population coverage with a primary series is less than 40% in 105 countries and less than 10% in 45 countries.

"Data provided by these two studies, along with other data regarding booster effectiveness and safety that are being generated, will provide valuable guidance for decision making in other countries, as the risk-benefit balance of introducing a booster dose is assessed," Patel wrote.

However, Patel emphasized the most useful tool in helping to combat the pandemic is vaccinating the unvaccinated.

"Vaccination with the primary series, especially in high-risk populations, remain a top priority everywhere, because this will ultimately lead to a greater reduction in severe disease and death," Patel added.