Coronavirus (COVID-19): state of the epidemic - 11 March 2022

Resilience: Vaccinations and Antibody Estimates

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. For more information, see the PHS weekly report.

By 9 March, over 4.4 million people had received their first dose, an estimated 92.3% of the population aged 12 and older, and almost 4.2 million people had received their second dose, an estimated 87.0% of the population aged 12 and older. Almost 3.5 million people in Scotland had received a third vaccine dose or booster, an estimated 72.3% of the population aged 12 and older^[53].

By 9 March, booster vaccine uptake is at least 91% for those aged 55 and over, 86% for those aged 50 to 54, 76% for those aged 40 to 49, 61% for those aged 30 to 39, 51% for those aged 18 to 29, 15% for those aged 16-17 and 1% for those aged 12 to 15^[54].

By local authority, the highest uptake of dose 3 or booster of the Covid-19 vaccination by 9 March was seen in East Dunbartonshire (82.1%), Argyll and Bute (79.8%), Shetland Islands (79.8%), Scottish Borders (79.4%), Orkney Islands (79.1%), and South Ayrshire (78.5%). The lowest uptake of dose 3 or booster of the Covid-19 vaccination by 9 March was seen in Edinburgh (68.8%), Glasgow City (62.2%), Dundee City (65.1%), and Aberdeen City (65.6%)^[55].

Antibodies Estimates

The ONS Covid-19 Infection Survey estimated that in the week ending 20 February 2022, 99.6% (95% credible interval: 99.4% to 99.7%) of the adult population (aged 16 or older) living in private residential households in Scotland would have tested positive for antibodies against SARS-CoV-2 at the standard threshold, as a result of having the infection in the past or being vaccinated. This compares to:

• 99.5% in England (95% credible interval: 99.3% to 99.6%),
• 99.4% in Wales (95% credible interval: 99.1% to 99.6%),
• 99.7% in Northern Ireland (95% credible interval: 99.4% to 99.9%).

In Scotland, estimates for the percentage of adults (aged 16+) testing positive for antibodies at the standard antibody threshold ranged from 98.8% in those aged 80 and over (95% credible interval: 97.4% to 99.4%) to 99.8% in those aged 50 to 59 and 65 to 69 (95% credible interval: 99.6% to 99.9%) in the week ending 20 February 2022.

Academic research on antibody thresholds using data from when the Delta variant was the dominant strain indicate that a higher threshold of antibodies is needed to provide protection from new Covid-19 infections for those who are vaccinated^[56]. In Scotland, 98.3% of the adult (aged 16 or older) population living in private residential households (95% credible interval: 97.8% to 98.6%) are estimated to have antibodies against SARS-CoV-2 at the higher antibody threshold of 179 ng/ml in the week ending 20 February 2022. In the same week, the percentage of children aged 8 to 15 years with levels of antibodies to SARS-CoV-2 at or above the higher antibody threshold of 179 ng/ml was also at a high level, and has been increasing across all UK countries in recent weeks.

This higher antibody threshold was identified as providing a 67% lower risk of getting a new Covid-19 infection with the Delta variant after two vaccinations with either Pfizer or AstraZeneca vaccines, compared with someone who was unvaccinated and had not had Covid-19 before^[57]. It is unlikely that this threshold will provide equivalent protection against the Omicron variant and ONs will keep the threshold used in the analysis of antibodies under regular review.

For context, the increase in the percentage of individuals recording antibody levels above the higher threshold value also coincides with the uptake of the booster vaccine in Scotland which started in September 2021. The modelled percentage of adults aged 16 years and over testing positive for antibodies to SARS-CoV-2, higher antibody threshold, in Scotland surpassed 90% by 26 December 2021^[58]. This is in line with 70% of Scotland's population aged 16 and over having received a third or booster dose by 26 December 2021^[59].

Vaccine Effectiveness Against Omicron

The Omicron variant (parent Pango lineage B.1.1.529) can be separated into three main groups: BA.1, BA.2 and BA.3. The original Omicron lineage, BA.1, was dominant in the UK, however, the BA.2 lineage of Omicron is now the dominant variant within Scotland based on unpublished data generated by PHS. Details of risk assessments for both BA.1 and BA.2 carried out by UKHSA can be found on the UK government's website^[60] and in the State of the Epidemic reports published on 4 February and 28 January 2022. The latest BA.2 risk assessment update issued on 25 February indicates that BA.2 has a growth advantage compared to BA.1, however it is likely that the clinical severity of BA.2 is similar to that of BA.1^[61].

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 after a Pfizer booster started at around 90% dropping to around 75% after 10 to 14 weeks. Moderna booster restored vaccine effectiveness against hospitalisation to around 90 to 95% up to 9 weeks after vaccination. The high level of protection against mortality was also restored after the booster dose with vaccine effectiveness of 95% 2 or more weeks following vaccination for those aged 50 and older^[62].

Vaccine effectiveness against symptomatic disease with BA.2 compared to BA.1, showed similar results with BA.1 having an effectiveness of around 10% and BA.2 having an effectiveness of around 18% after 25 or more weeks following the second dose. These estimates have large overlapping confidence intervals. The booster dose of vaccine increased effectiveness to around 69% for BA.1 and 74% for BA.2 at 2 to 4 weeks following a booster vaccine. Effectiveness dropped to around 49% for BA.1 and 46% for BA.2 10 weeks after vaccination^[63].

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^{[64] [65]}, with the most recent estimate of the risk of presentation to emergency care or hospital admission with Omicron was approximately half of that for Delta^[66]. A recent, non-peer reviewed UK study revealed that risk of COVID-19 related death was 67% lower for Omicron when compared with Delta^[67].