Decline in effectiveness of COVID vaccine suggests need for boosters


December 10, 2021 – The effectiveness of the two most common COVID-19 vaccines has declined over time in a group of older patients, suggesting that booster doses may be needed to protect recipients in the long term, according to a new study.

Also observed in this group of US veterans, who had a median age of 67 years: those who received “the Moderna vaccine consistently had higher antibody levels than recipients of the Pfizer-BioNTech vaccine, in all groups. ‘age and since vaccination,’ said Kristina L. Bajema, MD, of the CDC’s COVID-19 response team, and associates.

The efficacy of the Moderna vaccine was 89.6% 14 to 119 days after patients received the second dose, compared to 86.0% for the Pfizer vaccine. After 120 days or more, the vaccine’s efficacy had fallen to 86.1% for Moderna and 75.1% for Pfizer, investigators in the Morbidity and Mortality Weekly Report.

Levels of the relevant antibodies – anti-spike immunoglobulin (IgG) and anti-receptor binding domain (RBD) IgG – showed a similar pattern: lower after the 120 day mark for both vaccines, but higher at both time periods. for Moderna than for Pfizer. These differences in antibody levels are consistent with other studies, the researchers said, and may be the result of the higher antigen content of the Moderna vaccine and its longer interval between doses.

The 1,896 study veterans were enrolled while hospitalized with COVID-like illness at five veterans medical centers across the country (Atlanta, Houston, Los Angeles, New York, and Palo Alto, Calif.) . The group included patients who tested positive and those who tested negative for COVID-19 when they were first hospitalized; 799 were eventually fully vaccinated. About 58% of the group was 65 years of age or older.

Both vaccines were more effective in younger patients: 89.4% for those under 65 and 72.9% for those 65 and over in the Pfizer group, compared to 94.5% and 78.6%, respectively, for Moderna. The same drop in efficacy after 120 days was seen for both age groups, the researchers noted.

The effect of age can be of concern.

“Overall, for both vaccines, antibody levels in this cohort of older U.S. veterans with high prevalences of underlying medical problems were significantly lower than levels seen in healthy, younger volunteers or the health workers in other studies, ”they said, adding that this dose booster may be needed“ to help maintain long-term protection against severe COVID-19 ”.


Sara H. Byrd