Vaccine Offers Long-Term Protection Against Patient Mortality Caused by SARS-CoV-2 Infection

Two or 3 doses of the COVID-19 vaccine—either the BNT162b2 mRNA vaccine (Pfizer-BioNTech) or inactivated CoronaVac vaccine (Sinovac)—had a durable response over time against the infection, according to a recent study published in JAMA Network Open. Vaccine efficacy (VE) waned after dose 2, although the vaccine was still able to protect against severe outcomes caused by the SARS-CoV-2 Omicron variant.

“Our study suggested that both CoronaVac and BNT162b2 provide protection against severe outcomes caused by the Omicron variant and the VE waned consistently after the second dose,” the authors wrote. However, “vaccine recipients retained cellular immunity that protected against progression to severe COVID-19 even after neutralizing antibodies waned.”

The SARS-CoV-2 Omicron variant began circulating in late 2021. It rapidly spread throughout Hong Kong (location of the present study)—a city that that authors did not consider to be well-protected against the emerging Omicron variant—and caused high rates of mortality. By June 2022, 85% of the Hong Kong population received 2 doses of the BNT162b2 mRNA or inactivated CoronaVac vaccines; however, many older residents were still not boosted.

VE often wanes with time, but few studies have reviewed these waning effects against severe outcomes caused by the Omicron variant, according to the investigators. The current study evaluated VE changes on hospitalizations and mortality from the Omicron variant over time among people in Hong Kong.

The case-control study included 32,823 participants in the case group and 131,328 patients in the control group, using linked administrative data from the Department of Health in Hong Kong. The data revealed that patients aged 18 to 49 years who received 2 doses of CoronaVac were protected against death by 86.4%, whereas 2 doses of BNT162b2 protected against death by 92.9%.

Two doses of the vaccine were less effective on mortality among older adults. The VE was estimated to wane 6 months following the second dose.

“This finding echoed a study in Finland showing that VE against hospitalization 6 months after 2 doses of BNT162b2 was only 61% in older patients during the Omicron-dominant period,” the study authors wrote.

The booster dose combatted this risk—neutralization tests show that a third dose of the BNT162b2 created a 7-fold increase in antibody levels in adults aged 65 to 85 years. Although antibodies increased in patients older and younger than 60 years of age, the older patient population appeared to have more antibodies after a third dose.

Generally, patients who received 3 doses of the CoronaVac or a heterologous booster experienced VE that protected against risk of death by 85%.

The study includes some limitations, the first of which being that the investigators missed some cases due to underreporting, Additionally, investigators excluded patients in ICUs when defining disease severity, did not include data on immunocompromised status, and did not adjust for behavioral and lifestyle factors as confounders.

“A booster dose is recommended for older individuals to restore immunity,” the study authors wrote. “This is especially critical in a setting like Hong Kong, where coverage of the third dose of the vaccine is still insufficient among older residents.”

Reference

Wei Y, Jia K, Zhao S, et al. Estimation of Vaccine Effectiveness of CoronaVac and BNT162b2 Against Severe Outcomes Over Time Among Patients With SARS-CoV-2 Omicron. JAMA Netw Open. 2023;6(2):e2254777. doi:10.1001/jamanetworkopen.2022.54777