Coronavirus (COVID-19): state of the epidemic - 14 April 2022

Resilience: Vaccinations, Antibody Estimates, and Variants

Vaccinations

Vaccinations started in Scotland on 8 December 2020 and there has been a very high uptake. Covid-19 vaccines protect most people against severe outcomes of a Covid-19 infection, but some people will still get sick because no vaccine is 100% effective. The current evidence suggests that you may test positive for Covid-19 or be reinfected even if you are vaccinated, especially since the emergence of the Omicron variant in the UK. The major benefit of vaccination against Omicron is to protect from severe disease. More information is available on the PHS website.

As at 12 April, almost 4.4 million people had received their first dose, an estimated 90.4% of the population in Scotland aged 12 and older. Around 4.1 million people had received their second dose, an estimated 85.7% of the population aged 12 and older. Additionally, over 3.4 million people in Scotland had received a third vaccine dose, which is an estimated 72.4% of the population aged 12 and older^[66].

The JCVI now advise a spring booster dose of the Covid-19 vaccine for: adults aged 75 years and over, residents in care homes for older adults, and individuals aged 12 years and over who have a weakened immune system^[67]. By 12 April, 180,396 fourth dose vaccinations had been administered, with 50.9% of all care home residents having received their fourth dose^[68].

Antibodies Estimates

The analysis of antibody prevalence can be used to identify individuals who have had Covid-19 in the past or who have developed antibodies as a result of vaccination. As detailed by the ONS, there is a clear pattern between vaccination and testing positive for Covid-19 antibodies but the detection of antibodies alone is not a precise measure of the immunity protection given by vaccination.

The ONS Covid-19 Infection Survey estimated that in Scotland, 98.9% of the adult (aged 16+) population living in private residential households (95% credible interval: 98.5% to 99.1%) had antibodies against SARS-CoV-2 at the 179 ng/ml threshold, from a blood sample in the week beginning 14 March 2022. This would be as a result of having the infection in the past or being vaccinated. This compares to:

• 98.8% in England (95% credible interval: 98.5% to 99.0%),
• 98.8% in Wales (95% credible interval: 98.4% to 99.1%),
• 99.0% in Northern Ireland (95% credible interval: 98.4% to 99.4%)^[69].

The estimated percentage of the adult (aged 16+) population living in private residential households in Scotland testing positive for antibodies against SARS-CoV-2 at the 179 ng/ml threshold ranged from 98.0% for those aged 80 years and over (95% credible interval: 96.3% to 98.9%) and 99.4% for those aged 65 to 69 years (95% credible interval: 99.2% to 99.6%) and 70 to 74 years (95% credible interval: 99.1% to 99.6%), in the week beginning 14 March 2022^[70].

The percentage of children living in private residential households in Scotland who are estimated to have antibodies against SARS-CoV-2 at the 179 ng/ml threshold was 85.3% for those aged 8 to 11 years (95% credible interval: 75.5% to 91.8%) and 97.2% for those aged 12 to 15 years (95% credible interval: 94.6% to 98.6%), from a blood sample in the week beginning 14 March 2022.

Vaccine Effectiveness Against Omicron

The UKHSA reported that vaccine effectiveness against symptomatic disease, hospitalisation, or mortality with the Omicron variant is lower compared to the Delta variant and that it wanes rapidly. Vaccine effectiveness against all outcomes is restored after the booster dose, with effectiveness against symptomatic disease ranging initially from around 60% to 75% and dropping to around 25% to 40% after 15 weeks. Vaccine effectiveness against hospitalisation ranged from 85% to 95% up to six months after the booster dose with little variation between the type of vaccine used for priming or boost. The high level of protection against mortality was also restored after the booster dose with vaccine effectiveness of 95% two or more weeks following vaccination for those aged 50 and older^[71].

Vaccine effectiveness against symptomatic disease with Omicron BA.2 compared to Omicron BA.1, showed similar results, with BA.1 having an effectiveness of below 20% and BA.2 having an effectiveness of above 20% after 25 or more weeks following the second dose. The booster dose of vaccine increased effectiveness to around 70% for BA.1 and BA.2 at two to four weeks following a booster vaccine. Effectiveness dropped to around 50% for BA.1 and BA.2 15 weeks after vaccination. Vaccine effectiveness against hospitalisation ranged from 83% for BA.1 to 87% for BA.2 at 14 to 34 days after the booster dose, and dropped to 73% for BA.1 and 70% for BA.2 after 70 days. These estimates have large overlapping confidence intervals^[72].

More data on vaccine effectiveness against the Omicron variant can be found in the UKHSA vaccine surveillance reports. There is evidence that there is reduced overall risk of hospitalisation for Omicron compared to Delta^{[73] [74]}, with the most recent estimate of the risk of presentation to emergency care or hospital admission with Omicron approximately half of that for Delta^[75]. A recent, non-peer reviewed UK study revealed that risk of Covid-19 related death was 67% lower for Omicron when compared with Delta^[76].