By IDSE News Staff
Protection from SARS-CoV-2 is extended with a messenger RNA (mRNA) booster. But that defense wanes over time, signaling the need for an additional booster, according to a large new study from the CDC.
Investigators at the CDC’s VISION Network analyzed data from nearly 893,500 patients (≥18 years of age) taken from 261 hospitals, 272 emergency departments and 119 urgent care clinics across 10 states between Jan. 17, 2021, and July 12, 2022 (BMJ 2022;379:e072141). This period correlated with cycles of omicron dominance—including subvariants BA.4 and BA.5—and the periods before delta became dominant and afterward.
Vaccine effectiveness against COVID-19–related hospitalization was 94% in the pre-delta period and 96% in the delta-dominant period during the first two months after receiving a second dose. By months 4 and 5, vaccine effectiveness had waned to 87% and 89% in the pre-delta and delta-dominant periods, respectively.
The investigators found that in the omicron-dominant period, the mRNA vaccine protection yielded an 89% effective rate against severe illness from SARS-CoV-2 within the first two months after receipt, but waned to 66% by months 4 and 5.
A third booster dose restored high levels of protection against hospital admissions and emergency department or urgent care visits, but then also waned. The analysis of the data taken from hospitals showed the vaccine effectiveness of three doses was initially 96% during the delta period and 83% during the omicron-dominant period. Effectiveness began to wane by four to five months after the third dose during the omicron period. Investigators reported vaccine effectiveness against hospital admission decreased to 66% and 46% against emergency department or urgent care visits.
The waning effect was documented across all subgroups, including young adults and people who were immunocompetent. However, the investigators noted vaccine effectiveness waned more significantly in individuals who were immunocompromised.
The investigators said the protection conferred by the mRNA vaccines against moderate and severe COVID-19 infections waned during the months after primary vaccination, increased substantially after the third dose and then waned again after four to five months. They said a fourth dose improved vaccine effectiveness among those recommended for an additional booster.
The investigators concluded the documented waning of vaccine effectiveness among adults of all ages supports recommendations for a third vaccine dose and consideration of additional booster doses in the future.
