Vaccine provides long-term protection against patient mortality caused by SARS-CoV-2 infection

According to a recent study published in JAMA network open. Vaccine efficacy (VE) decreased after dose 2, although the vaccine was still able to protect against severe consequences caused by the SARS-CoV-2 Omicron variant.

“Our study suggested that CoronaVac and BNT162b2 provide protection against the severe consequences caused by the Omicron variant and that VE decreased 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 quickly spread throughout Hong Kong (location of this study) – a city the authors did not consider to be well protected against the emerging variant of Omicron – and caused a high mortality rate. By June 2022, 85% of Hong Kong’s population had received 2 doses of BNT162b2 mRNA or inactivated CoronaVac vaccines; however, many older residents were still unstimulated.

VE often declines over time, but few studies have examined these diminishing effects against the severe consequences caused by the Omicron variant, the researchers say. The current study assessed changes in VE on Omicron variant hospitalizations and mortality over time in 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 Hong Kong Department of Health. The data revealed that patients aged 18-49 who received 2 doses of CoronaVac protected against death by 86.4%, while 2 doses of BNT162b2 protected against death by 92.9%.

Two doses of the vaccine were less effective on mortality in the elderly. VE was estimated to decline 6 months after the second dose.

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

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

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

The study has some limitations, the first being that the investigators missed some cases due to under-reporting. In addition, investigators excluded intensive care unit patients when defining disease severity, did not include data on immunocompromised status, and did not adjust for behavioral and style factors. life. as confusing.

“A booster dose is recommended for the elderly to restore immunity,” the study authors wrote. “This is particularly 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. Estimated Vaccine Efficacy of CoronaVac and BNT162b2 Against Severe Outcomes Over Time in SARS-CoV-2 Patients Omicron. JAMA Netw Open. 2023;6(2):e2254777. doi:10.1001/jamanetworkopen.2022.54777