Vaccine surveillance report

 UK Health Security Agency

 COVID-19 vaccine surveillance report Week 42

Contents

Summary

Vaccine effectiveness 

 Population impact

Vaccine effectiveness 

Effectiveness against symptomatic disease 

 Effectiveness against hospitalisation

 Effectiveness against mortality

 Effectiveness against infection 

 Population impact

 Vaccine coverage

Vaccination status 

Vaccine impact on proportion of population with antibodies to COVID-19 

Summary of impact on hospitalisations, infections and mortality

 References

Summary

Four coronavirus (COVID- 19) vaccines have now been approved for use in the UK. Rigorous clinical trials have been undertaken to understand the immune response, safety profile and efficacy of these vaccines as part of the regulatory process. Ongoing monitoring of the vaccines as they are rolled out in the population is important to continually ensure that clinical and public health guidance on the vaccination programme is built upon the best available evidence. 

UK Health Security Agency, UKHSA, formerly Public Health England (PHE), works closely with the Medicines and Healthcare Regulatory Agency (MHRA), NHS England, and other government, devolved administration and academic partners tO monitor the COVID-19 vaccination programme. Details of the vaccine surveillance strategy are set on the page COVID-19: vaccine surveillance strategy (1). AS with all vaccines, the safety of COVID-19 vaccines is continuously being monitored by the MHRA They conclude that overal, the benefits COVID-19 vaccines outweigh any potential risks (2).

 Vaccine effectiveness

Several studies of vaccine effectiveness have been conducted in the UK which indicate that 2 doses of vaccine are between 65% and 95% effective at preventing symptomatic disease with COVID-19 with the Delta variant, with higher levels of protection against severe disease including hospitalisation and death. There is some evidence of waning of protection against infection and symptomatic disease over time, though protection against severe disease remains high in most groups at least 5 months after the second dose

 Population impact

The impact of the vaccination programme on the population is assessed by taking into account vaccine coverage, evidence on vaccine effectiveness and the latest COVID-19 disease surveillance indicators. Vaccine coverage tells us about the proportion of the population that have received 1 and 2 doses of COVID-19 vaccines. By 10 October 2021, the overall vaccine uptake in England for dose 1 was 65.5% and 60.4% for dose 2. In line with the programme rollout, coverage is highest in the oldest age groups.

 We present data on COVID-19 cases, hospitalisations and deaths by vaccination status. 

Based on antibody testing of blood donors, 98.0% of the adult population now have antibodies to COVID-19 from either infection or vaccination compared to 18.7% that have antibodies from infection alone.

Vaccine effectiveness

Large clinical trials have been undertaken for each of the COVID-19 vaccines approved in the UK which found that they are highly efficacious at preventing symptomatic disease in the populations that were studied. The clinical trials have been designed to be able to assess the efficacy of the vaccine against laboratory confirmed symptomatic disease with a relatively short follow up period so that effective vaccines can be introduced as rapidly as possible. 

Nevertheless, understanding the effectiveness against different outcomes (such as severe disease and onwards transmission), effectiveness in different subgroups of the population and understanding the duration of protection are equally important in decision making around which vaccines should be implemented as the programme evolves, who they should be offered to and whether booster doses are required

 Vaccine effectiveness is estimated by comparing rates of disease in vaccinated individuals to rates in unvaccinated individuals. Below we outline the latest real-world evidence on vaccine effectiveness from studies in UK populations. We focus on data related to the Delta variant which is currently dominant in the UK. The findings are also summarised in Table 1.

 Effectiveness against symptomatic disease

Vaccine effectiveness against symptomatic COVID-19 has been assessed in England based on community testing data linked to vaccination data from the National Immunisation Management System (NIMS), cohort studies such as the COVID Infection Survey and GP electronic health record data. After 2 doses, observed vaccine effectiveness against symptomatic disease with the Delta variant reaches approximately 65 to 70% with AstraZeneca Vaxzevria and 80 to 95% with Pfizer-BioNTech Comirnaty and Moderna Spikevax (3, 4) Vaccine effectiveness is generally slightly higher in younger compared to older age groups. With both Vaxzevria and Comirnaty, there is evidence of waning of protection over time, most notably among older adults. There is not yet enough follow-up with Spikevax to assess waning (3) 

Data (based primarily on the Alpha variant) suggest that in most clinical risk groups, immune response to vaccination is maintained and high levels of VE are seen with both the Pfizer and AstraZeneca vaccines. Reduced antibody response and vaccine effectiveness were seen after one dose of vaccine among the immunosuppressed group, however, after a second dose the reduction in vaccine effectiveness is smaller (5).

 Analyses by dosing interval suggest that immune response to vaccination and vaccine effectiveness against symptomatic disease improves with a longer (greater than 6 week interval) compared to a shorter interval of 3 to 4 weeks (6, 3)

Effectiveness against hospitalisation

Several studies have estimated vaccine effectiveness against hospitalisation in older ages, all of which indicate higher levels of protection against hospitalisation with all vaccines against the Alpha variant (7, 8, 9, 10). Effectiveness against hospitalisation of over 90% is also observed with the Delta variant with all 3 vaccines (3). In most groups there is relatively limited waning of protection against hospitalisation over a period of at least 5 months after the second dose. Greater waning appears to occur among those in clinical risk groups (3)

 Effectiveness against mortality

High levels of protection (over 90%) are also seen against mortality with all 3 vaccines and against both the Alpha and Delta variants (7, 11, 3). Relatively limited waning of protection against mortality is seen over a period of at least 5 months.

 Effectiveness against infection

Although individuals may not develop symptoms of COVID-19 after vaccination, it is possible that they could still be infected with the virus and could transmit to others. Understanding how effective vaccines are at preventing infection is therefore important to predict the likely impact of the vaccination programme on the wider population. In order to estimate vaccine effectiveness against infection, repeat asymptomatic testing of a defined cohort of individuals is required. Studies have now reported on vaccine effectiveness against infection in healthcare workers, care home residents and the general population (12, 13, 14,15). With the delta variant, vaccine effectiveness against infection has been estimated at around 65% with Vaxzevria and 80% with Comirnaty (4).

Effectiveness against transmission

As described above, several studies have provided evidence that vaccines are effective at preventing infection. Uninfected individuals cannot transmit; therefore, the vaccines are also effective at preventing transmission. There may be additional benefit, beyond that due to prevention of infection, if some of those individuals who become infected despite vaccination are also at a reduced risk of transmitting (for example, because of reduced duration or level of viral shedding). A household transmission study in England found that household contacts of cases vaccinated with a single dose had approximately 35 to 50% reduced risk of becoming a confirmed case of COVID-19. This study used routine testing data so would only include household contacts that developed symptoms and went on to request a test via pillar 2. It cannot exclude asymptomatic secondary cases or mildly symptomatic cases who chose not to request a COVID-19 test (16). Data from Scotland has also shown that household contacts of vaccinated healthcare workers are at reduced risk of becoming a case, which is in line with the studies on infection (17). Both of these studies relate to a period when the Alpha variant dominated. An analysis from the ONS Community Infection Survey found that contacts of vaccinated index cases had around 65 to 80% reduced odds of testing positive with the Alpha variant and 35 to 65% reduced odds of testing positive with the Delta variant compare to contacts of unvaccinated index cases (18).

A summary of vaccine effectiveness evidence can be seen in Table 1.

Table 1. Summary of evidence on vaccine effectiveness against different outcomes Delta

•Outcome ; Vaccine effectiveness*: Pfizer-BioNTech  Cominarty¹ ; AstraZeneca Vaxzevria² ; Moderna Spikevax³.]

•Infection ; 75-85%¹; 60-70%²; —³.

•Symptomatic disease ; 80-90%¹; 65-75%²; 90-99%³.

•Hospitalisation ; 95-99%¹, 90-99%²; 95-99%³.

•Mortality ; 90-99%¹; 90-95%²; —³.

High Confidence =  Evidence from multiple studies which is consistent and  comprehensive 

Medium Confidence = Evidence is emerging from a limited number of studies or with a moderately level of uncertainty 

Low Confidence = Little evidence is available at present and results are inconclusive 

*Estimates of initial vaccine effectiveness in the general population after a 2 dose course. This typically applies for at least the first 3 to 4 months after vaccination. For some outcomes there may be waning of effectiveness beyond this point.

Population impact

Vaccines typically have both direct effects on those who are vaccinated and indirect effects on the wider population due to a reduced probability that people will come into contact with an infected individual. The overall impact of the vaccination programme may therefore extend beyond that estimated through vaccine effectiveness analysis.

 Estimating the impact of a vaccination programme is challenging as there is no completely unaffected control group. Furthermore, the effects of the vaccination programme need to be differentiated from that of other interventions (for example, lockdowns or outbreak control measures), changes in behaviour and any seasonal variation in COVID-19 activity. 

UKHSA and other government and academic partners monitor the impact of the vaccination programme on levels of COVID-19 antibodies in the population and different disease indicators, including hospitalisations and mortality. This is done through population- based testing and through modelling which combines vaccine coverage rates in different populations, estimates of vaccine effectiveness and disease surveillance indicators,

 Vaccine coverage

Please note that in order to undertake preparatory work prior to a change in the definition of age-cohorts and to ensure alignment across publications of weekly data, data on vaccine uptake are not being updated this week. Normal publication willesume next week. Daily figures on uptake can be found on the COVID-19 Data Dashboard.

 The data in this week's report covers the period from 8 December 2020 to 10 October 2021 (week 40) (Figure 1). It shows the provisional number and percentage of people in England who have had received 1 dose or 2 doses of a COVID-19 vaccination by age group and week since the start of the programme.

 Up to 30 September 2021 84,122 women of child-bearing age in England (under 50) who reported that they were pregnant or could be pregnant at the time received at least one dose of COVID-19 vaccination and of these, 67,144 have received their second dose. This is in response to the self-reported pre-screening question "Are you or could you be pregnant?". The true number of pregnant women who have had a COVID-19 vaccination is likely to be greater than this

 Please note that pregnant women are not a separate priority group as defined by JCVI who have advised that "women who are pregnant should be offered vaccination at the same time as non-pregnant women, based on their age and clinical risk group" therefore comparing vaccine uptake in pregnant women to other vaccination programmes is not currently appropriate. The MHRA closely monitors the safety of COVID-19 vaccine exposures in pregnancy, including Yellow Card reports for COVID-19 vaccines used in pregnancy, for the latest information please see the webpage Coronavirus vaccine - weekly summary of Yellow Card reporting.

Vaccination status

Vaccination status of COVID-19 cases, deaths and hospitalisations by week of specimen date over the past 4 weeks up to week 41 (up to 17 October 2021) are shown in Table 2 to 4 and Figure 2 .

 Please note that data on vaccine uptake are not being updated this week, and as such the population sizes used to calculate rates relate to last week's data.

 Methods

COVID-19 cases and deaths identified through routine collection from the Second Generation Surveillance System (SGSS) and from UKHSA EpiCel's deaths data as described here, were linked to the National Immunisation Management System (NIMS) to derive vaccination status. using an individual's NHS number as the unique identifier. 

Attendance to emergency care at NHS trusts was derived from the Emergency Care DataSet (ECDS) managed by NHS Digital. The same data source was used to identify COVID-19 cases where the attendance to emergency care resulted in admission to an NHS trust. 

ECDS is updated weekly, and cases are linked to these data twice weekly. Data from ECDS are subject to reporting delays as, although NHS trusts may update data daily, the mandatory deadline for submission is by the 21st of every month. This means that for weeks immediately following the 21st of a month, numbers may be artificially low and are likely to be higher in later versions of the report .

Data from ECDS also only report on cases who have been presented to emergency care and had a related overnight patient admission and do not show those who are currently in hospital with COVID-19. As such, it is not appropriate for use for surveillance of those currently hospitalised with COVID-19. In addition, these data will not show cases who were directly admitted as inpatients without presenting to emergency care. 

The outcome of overnight inpatient admission following presentation to emergency care, was limited to those occurring within 28 days of the earliest specimen date for a COVID-19 case. 

Deaths include those who died (a) within 28 days of the earliest specimen date or (b) within 60 days of the first specimen date or more than 60 days after the first specimen date with COVID- 19 mentioned on the death certificate. 

The rate of COVID-19 cases, hospitalisation, and deaths in fully vaccinated and unvaccinated groups was calculated using vaccine coverage data for each age group extracted from the National Immunisation Management Service.

Results

The rate of a positive COVID-19 test varies by age and vaccination status. The rate of a positive COVID-19 test is substantially lower in vaccinated individuals compared to unvaccinated individuals up to the age of 29. In individuals aged greater than 30, the rate of a positive COVID-19 test is higher in vaccinated individuals compared to unvaccinated. This is likely to be due to a variety of reasons, including differences in the population of vaccinated and unvaccinated people as well as differences in testing patterns.

 The rate of hospitalisation within 28 days of a positive COVID-19 test increases with age, and is substantially greater in unvaccinated individuals compared to vaccinated individuals. 

The rate of death within 28 days or within 60 days of a positive COVID-19 test increases with age, and again is substantially greater in unvaccinated individuals compared to fully vaccinated individuals.

 Interpretation of data

These data should be considered in the context of vaccination status of the population groups shown in the rest of this report. The vaccination status of cases, inpatients and deaths is not the most appropriate method to assess vaccine effectiveness and there is a high risk of misinterpretation. Vaccine effectiveness has been formally estimated from a number of different sources and is described earlier in this report.

 In the context of very high vaccine coverage in the population, even with a highly effective vaccine, it is expected that a large proportion of cases, hospitalisations and deaths would occur in vaccinated individuals, simply because a larger proportion of the population are vaccinated than unvaccinated and no vaccine is 100% effective. This is especially true because vaccination has been prioritised in individuals who are more susceptible or more at risk of severe disease, Individuals in risk groups may also be more at risk of hospitalisation or death due to non- COVID-19 causes, and thus may be hospitalised or die with COVID-19 rather than because of COVID-19.

 The case rates in the vaccinated and unvaccinated populations are crude rates that do not take into account underlying statistical biases in the data. There are likely to be systematic differences in who chooses to be tested and the COVID risk of people who are vaccinated.

 These biases become more evident as more people are vaccinated and the differences between the vaccinated and unvaccinated population become systematically different in ways that are not accounted for without undertaken formal analysis of vaccine effectiveness as is made clear.

 NIMS is used as a denominator because it is a database of named individuals eligible for vaccination in which there is a record of each individual's vaccination status.

Table 2. COVID-19 cases by vaccination status between week 38 and week 41, 2021

1. Cases reported by specimen date between week 38 and week 41 2021;

2. Total ;

3. Unlinked*

4. Not vaccinated

5. Received one dose (1-20 days before spocimen date)

6. Received one dose, ≽21 days before specimen date 

11.001 8.404 6,545 3,800 1.632 617 215 215

7. Second dose ≽14 days before specimen date

8. Rates among persons vaccinated with 2 doses (per 100,000)

9. Rates among persons not vaccinated (per 100,000)

1

• Under 18 

•18-29 

•30-39 

•40-49 

•50-59

•60-69

•70-79 

• ≽80

2

•397.882 

•62,885 

•92,257 

•130,904 

•88,020 

•45,155 

•27,360 

•11,907

3

• 24.292 

•7,512 

•7,346 

•7,297 

•4,790 

•2,614 

•1,559 

•854

4

• 351,148 

•20,902 

•21,726 

•13,022 

•5,399 

•1,872 

•658 

•382

5

•10,698; 

•758; 

•636; 

•293; 

•80; 

•24; 

•12; 

•7

6

•11,001 

•8,404 

•6,545 

•3,800 

•1,632 

•617 

•215 

•215

7

• 743 

•25,309 

•56,004 

•106,492 

•76,119 

•40,028 

•24,916 

•10,449

8

•314.1 

•462.1 

•966.7 

•1,731.3 

•1,075.3 

•704.1 

•537.9 

•408.8

9

•3,013.6 

•615.4 

•751.1 

•772.9 

•528.6 

•347.1 

•267.6 

•304.1

 *Individuals whose NHS numbers were unavailable to link to the NIMS

 **Interpretation of the case rates in vaccinated and unvaccinated population is particulariy susceptible to changes in denominators and should be interpreted with extra caution.