COVID-19 in 2021: Higher mortality rate among unvaccinated population

COVID-19 deaths in Malaysia were consistently lower among vaccinated populations versus unvaccinated in the 7 months following the vaccine rollout, according to a recent study.

A recent retrospective analysis by a cross-university team from Malaysia and Singapore examined data on the 20,823 COVID-19 deaths in Malaysia between 24 February to 14 September 2021, as released by the MOH for public use on open-source platform GitHub. [Lancet Reg Health West Pac 2022;18:100354. Available at https://doi.org/10.1016/j.lanwpc.2021.100354]

This data was organized by vaccination status (unvaccinated, partially or fully vaccinated) and vaccine type (BNT162b2 mRNA, inactivated whole-virion, or ChAdOx1), and stratified by age and comorbidities.* The team then calculated age-standardized mortality rate per 100,000 population (ASMR) among the different populations.

The numbers of deaths per 100 000 persons, in any population is influenced by the age distribution of the population. ASMR adjusts for these differences in the calculation of the death rates.

In general, the median age of those who died from COVID-19 in the period was 61.0 years (interquartile range 49–72 years), with 24 percent of deaths occurring in the 60–69 years age group (4,946 individuals). More deaths occurred among men than women (1.33:1 ratio).

The study group reported that overall ASMR for the unvaccinated population (47.5 per 100,000 individuals) was 43.2 times higher than those fully vaccinated with BNT162b2 (1.1 per 100,000) and 12.5 times higher than those fully vaccinated with inactivated whole-virion (3.8 per 100,000). Partial vaccination with any vaccine also seemed to provide significant reductions in ASMR compared to non-vaccination.

The study also did not provide an inference regarding vaccine effectiveness, as it lacked detailed information regarding those who received the vaccine but avoided infection or death.

Comorbidities add risk for all

Within the vaccinated population, higher ASMR was seen in individuals with comorbidities versus those without. ASMRs for those with comorbidities were 8.9 times, 4.1 times, and 1.5 times higher than those without comorbidities among recipients of BNT162b2, inactivated vaccine, and ChAdOx1 vaccine, respectively.

“In this study, we could not further describe the risk of death by the types of comorbidities. Nevertheless, other studies in Malaysia have reported that persons with diabetes, hypertension, kidney diseases, heart diseases, and cancer were at higher risk of COVID-19-related deaths,” said the authors.

A noted data limitation was that vaccine allocation was not randomized; BNT162b2 was prioritized for frontline workers and older adults with comorbidities. The ChAdOx1 vaccines were allocated on a voluntary opt-in basis due to initial safety concerns, which may have led to a mostly younger population (at lower risk of severe illness) compared to the other vaccine groups.

A need for boosters

The study also found among vaccinated individuals, the ASMR of those who received inactivated vaccines was higher than the recipients of the BNT162b2 and ChAdOx1 vaccines.

“While we did not analyse immunological data […] the higher mortality rate among recipients of inactivated vaccines calls for close monitoring of breakthrough infections and deaths by vaccine types and further investigations into the recipients’ immunological profiles,” noted the authors. They highlighted a Hong Kong study which found lower concentrations of neutralizing antibodies in recipients of inactivated versus BNT162b2 vaccines. [Lancet Microbe 2021;2(9):e423]

“Our study findings also concur with the recent recommendations by the WHO to offer a third dose to persons aged ≥60 who received inactivated vaccines,” they added.