While clinical trials assess the effectiveness of a vaccine, such trials are not designed to designed to assess the population impact of vaccination.
The efficacy of the currently available vaccines has been demonstrated in clinical studies but of greater importance, is an assessment of the real-world effectiveness, especially the effect on disease severity leading to hospitalisation and potentially death. A good deal of evidence on the impact of the COVID-19 vaccination programme has been gathered from Israel. As with the UK, the programme began in December 2020 and by February 2021, over 84% of people aged 70 years and older had received a second dose of the BNT162b2 vaccine.
Armed with this trove of data, a team from the Department of Public Health, Ben-Gurion University, Beer-Sheva, Israel, undertook an ecologic study to assess the effect of the BNT162b2 vaccine on the occurrence of severe disease. The researchers looked at the need for mechanical ventilation among hospitalised patients as a proxy measure of the severity of infection, among those who had already received a dose of the vaccine. The researchers examined the comparative number hospitalised patients needing mechanical ventilation aged 70 years and over with those under 50 years. Data on the number of people in receipt of mechanical ventilation were obtained from the Israel Ministry of Health COVID-19 dashboard.
By 9 February 2021, a total of 2,224,176 people had received a second vaccine dose, of which 84.3% were aged 70 and over and 9.9% were aged less than 50. During the period between October 2020 and December 2020, there were 15 and 84 people aged over 70 and under 50 respectively, who were in hospital and needed mechanical ventilation, giving a mean ratio 5.8:1 (> 70 to <50 years). However, by 9 February, the 7-day rolling average of hospitalised and ventilated patients aged over 70 years was 109 compared to 57.7 in those under 50. Thus, the ratio had reduced by 67% to 1.9:1 compared with the October to December figures.
The authors concluded that this represents the first evidence that, at a population level, the vaccine programme is leading to a reduced risk of severe COVID-19 and helping to limit the spread of disease.
Rinott E, Youngster I, Lewis YE. Reduction in COVID-19 Patients Requiring Mechanical Ventilation Following Implementation of a National COVID-19 Vaccination Program — Israel, December 2020–February 2021. MMWR Morb Mortal Wkly Rep 26th February 2021 doi:http://dx.doi.org/10.15585/mmwr.mm7009e3