COVID-19: analysing first vaccine effectiveness in the UK

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On 8 December 2020, the UK became the first country to rollout a COVID-19 vaccination programme, initially using the Pfizer-BioNTech vaccine.

Following advice from the Joint Committee on Vaccination and Immunisation (JCVI), care home residents and staff, people over the age of 80 and health and social care workers were the first to receive the vaccine.

The programme was extended to those aged over 75 and then over-70s and the clinically extremely vulnerable. By 15 February 2021, everyone in these four priority groups had been offered the first dose of the vaccine.

Since the beginning of the vaccination programme, Public Health England (PHE) has been monitoring the effectiveness of COVID-19 vaccines in the real world and has now published its first analysis of the impact of the Pfizer-BioNTech vaccine on:

  • Any infection (symptomatic or asymptomatic)
  • symptomatic disease
  • hospitalisation
  • death

Vaccine effectiveness against any COVID-19 infection (SIREN)

What does it show?

PHE’s SIREN (Sarscov2 Immunity & REinfection EvaluatioN) study shows that healthcare workers were 72% less likely to develop infection (with or without symptoms) after one dose of the vaccine, rising to 86% after the second dose.

Protection starts after two weeks. This protection will help to reduce the spread of infection, thus protecting the whole population – as you cannot spread the virus if you don’t have infection.

How was this worked out?

The SIREN study is following around 40,000 healthcare workers over a 12-month period to investigate COVID-19 reinfection rates and immune response. As part of the study, participants are tested every two weeks, whether or not they have symptoms.

By comparing the number of vaccinated participants with no previous infection who test positive for COVID-19 with the number of unvaccinated participants who receive a positive result, we can estimate how effective the vaccine is at preventing infection.

Of the SIREN participants, 15,121 had not previously tested positive when the vaccination programme started and were included in vaccine effectiveness analysis. The data go up to 8 February 2021.

Vaccine effectiveness against symptoms of COVID-19 in older people

What does it show?

Protection from any COVID-19 symptoms in over-80s is 57% from four weeks after vaccination. After the second dose, effectiveness rises to more than 85%.

How was this worked out?

12,754 over-80s who reported symptoms of COVID-19 and tested positive between 8 December 2020 and 12 February 2021 were included in the analysis.

By comparing how many of them were vaccinated when symptoms first appeared to how many were unvaccinated, we can estimate how effective the vaccine is at preventing symptomatic disease.

We then compared admission rates and death rates in cases in over-80s who were vaccinated compared to cases who were not. As the length of follow up is still quite limited, these data should be treated with caution.

Impact of vaccination on hospitalisation

What does it show?

Hospitalisation rates are falling in all age groups. However, people aged 75 and over, who were among the first to be offered vaccination, are seeing the fastest decline.

Those over 80 who develop COVID-19 infection after vaccination are around 40% less likely to be hospitalised than someone with infection who has not been vaccinated.

However, people who are vaccinated are less likely to catch COVID-19 in the first place.

How was this worked out?

Risk of admission within 21 days of sample date in those aged over 80 years with a confirmed PCR positive test was compared for cases with a history of vaccination at least 14 days before onset.

Impact of vaccine on the risk of death

What does it show?

Death rates are declining in all age groups. However, the rate of decline is slightly faster in the oldest age groups who have already been offered vaccination. This is in contrast to the first lockdown, when deaths in these age group stayed high for longer than younger age groups.

In older people (aged over 80) who develop COVID-19 infection, those who are vaccinated have a much lower chance of death (about 56% lower) than someone with infection who hasn’t been vaccinated.

How was this worked out?

Mortality in PCR positive cases is determined by linking on a daily basis to the Demographic Batch Service (DBS) to check NHS patient records for reports of individuals who died in the previous 24 hours.

Case fatality ratio within 14 days of a confirmed PCR positive test was lower in cases aged over 80 and vaccinated at least 14 days before onset than in unvaccinated cases. This indicates that within vaccinated individuals who do become symptomatic cases, the vaccine confers additional protection against death.

What does this mean?

Taken altogether, this means a single dose of the vaccine is providing a very high level of protection against hospitalisation and death from COVID-19.

When combining the lower risk of hospitalisation and deaths with our estimate for vaccine effectiveness against symptomatic disease, this suggest that a single dose of Pfizer-BioNTech vaccine is over 75% effective at preventing hospitalisation and death from COVID-19.

When added to the reduced spread from vaccinating health and social care workers, this means that our older population are now much better protected from COVID-19.

If the first dose is only 57% effective in those aged over 80, does this mean the decision to prioritise the first dose was wrong?

These data show clear protection from the first dose, particularly against severe disease, supporting the decision to maximise the number of people vaccinated with a single dose, as advised by the JCVI.

The current dosing strategy will save more lives by ensuring more people receive protection from severe disease following the first dose.

There is also good evidence suggesting that giving the second dose of AstraZeneca later will lead to much higher levels of protection. Offering the booster at twelve weeks will therefore help to ensure longer lasting protection beyond the current restrictions.

Data from Public Health Scotland show the Pfizer-BioNTech and AstraZeneca vaccines reduced the risk of hospitalisation from COVID-19 in up to 85% and 94%, respectively. Why is your data different to this?

These analyses used different methodologies. Both Scotland and England’s data show high levels of protection against hospitalisation and further analysis from PHE to be published in due course will show similar levels of protection to those observed in the Scotland study.

How does this compare to other countries?

These data are compatible with what is being seen in other countries, like Israel, although most cases in the UK are now of the variant of concern (B.1.1.7) first identified in South East England in December 2020 (the so-called Kent variant). This suggests that the vaccines are working against this variant.

What next?

We are just beginning to see a slightly higher rate of decline amongst hospitalisations and deaths in the age groups that have been offered vaccination. This is expected to increase over the next two weeks.

PHE is also monitoring the real-world impact of the AstraZeneca vaccine and will publish these findings in due course – but early signals in the data suggest it is providing similar protection to Pfizer-BioNTech after one dose.

Read our blog answering common questions about COVID-19 vaccination.