Vaccine efficacy against the severity of COVID-19 in the elderly
Vaccine efficacy against the severity of COVID-19 in the elderly

Vaccine efficacy against the severity of COVID-19 in the elderly

A recent study posted to medRxiv* Pre-print server evaluated vaccine efficacy (VE) for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in elderly patients before and after the spread of the SARS-CoV-2 Omicron variant of concern (VOC).

Examination: High vaccine efficacy against severe Covid-19 in the elderly in Finland before and after the advent of Omicron. Image credit: Rido / Shutterstock

SARS-CoV-2 vaccines have played a contributing role in curbing the impact of the 2019 pandemic with coronavirus disease (COVID-19). However, with the advent of new SARS-CoV-2 VOCs, VE against infections caused by the VOCs requires extensive research.

About the study

This study estimated VE of SARS-CoV-2 vaccines against the severity of the disease, related hospitalizations and intensive care units (ICU) admissions in elderly COVID-19 patients in Finland after two and three vaccine doses. The study also assessed the effect of SARS-CoV-2 Omicron VOC infection on elderly patients.

The study population included people aged 70 and over, while demographic data at the individual level were retrieved from the population information system in Finland. Data such as age, gender, residence, hospital stay, influenza vaccination, hospitalization time from 2015 to 2019, and comorbidities were also collected.

The team evaluated the differences between the three approved vaccine brands, namely Spikevax, Vaxzevria and Comirnaty, and the number of doses administered of each vaccine. The study also considered the time elapsed since vaccination at specific time points, for example 21 and 84 days after the first dose, 14, 91 and 181 days after the second dose, and 14 and 61 days after the third dose.

The primary outcome of this study was the duration between COVID-19 related hospitalization and a SARS-CoV-2 positive polymerase chain reaction (PCR) test. COVID-19-related hospitalizations were defined as patient hospitalization with the primary diagnosis of COVID-19, acute respiratory infections, or severe complications of lower respiratory tract infections. A timely association of hospitalization with COVID-19 infection occurred only if the patient was tested COVID-19 positive 14 days before or seven days after hospitalization.

The secondary outcome was evaluated for COVID-19-related intensive care unit, which was considered SARS-CoV-2-related if the patient’s physician marked it or if the patient tested COVID-19-positive during the hospital stay. ICU admissions were identified on the basis of patient record data obtained from the Finnish Intensive Care Consortium’s quality register for intensive care.


The study results showed that out of the 897,932 people who qualified for the study, 4% were unvaccinated, 6% were vaccinated with two doses of Comirnaty vaccine, and 66% were vaccinated with three doses of Comirnaty. There was a dosing interval of 84 days between the first and second doses and 187 days between the second and third doses.

There were 637 unvaccinated individuals among the 1,522 COVID-19 inpatients and 131 unvaccinated individuals among the 234 intensive care units. Within 14 to 90 days and 91 to 180 days after administration of the second dose of Comirnaty, 93% and 87% of hospital admissions against hospitalization were observed. These values ​​increased to 96% within 14 to 60 days after the third dose of vaccination. VE against ICU hospitalization at these times was higher than against hospitalization. A 76% VE was also found against hospitalization after two homologous doses of Vaxzevria in the first 91 to 180 days.

A slight decrease in RE as a subject of increasing age and the presence of comorbidities was also observed. In people aged 70 to 79 years, Comirnatys VE after the second dose was 95% in the first 14 to 90 days and 88% in the 91 to 180 days; whereas VE at the same times corresponded to 89% and 83% for patients aged 80 to 89 years, respectively. The presence of predisposed comorbidities lowered VE from 92% to 83% in the 91 to 180 days after administration of the second Comirnaty vaccine dose, whereas a 99% to 95% reduction was found 14 to 60 days after the third Comirnaty -dosage.

Comirnaty’s VE against COVID-19 related hospitalization in the fourth quarter of 2021 was 90% in the first 14 to 90 days after the second vaccination, which increased to 96% in the 14 to 60 days after the third vaccination, while the same in the SARS The CoV-2 Omicron-dominated first quarter of 2022 was 91% and 95%, respectively. While in the fourth quarter no significant difference was found in VE 14 to 90 days and 91 to 180 days after the second dose, VE was reduced in the first quarter to 76% in 91 to 180 days after the second dose.


Overall, the results of the study showed that COVID-19 vaccines have provided adequate protection against COVID-19-related hospitalization and hospitalization in the intensive care unit of the elderly high-risk population. The team also found evidence of decreasing RE in the first six months after vaccination with the two-dose series, while the third dose significantly improved VE for at least two to three months after administration of the third dose.

*Important message

medRxiv publishes preliminary scientific reports that are not peer-reviewed and therefore should not be considered as crucial, guide clinical practice / health-related behavior or be treated as established information.

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