This is a pilot study to assess the feasibility of establishing a national sero-epidemiological survey in England in individuals aged 0-24 years, focusing on assessing humoral immunity against diphtheria, Group C invasive meningococcus and SARS-CoV-2. The investigators will recruit 2800 to 3800 individuals, divided into three groups:

Group one (N= 2300):

This will include all age groups (0-24years), with recruitment restricted by postcodes provided by Public Health England (PHE) to recruit a representative population for the region as assessed by the IMD (Index of Multiple Deprivation scores).

Group two (N= up to 1200):

This group has been added following additional funding to enhance the sample size in response to the COVID-19 pandemic. This will recruit 0-19 year olds and will not be restricted by post code sampling. Instead recruitment will be by public promotion within the normal recruiting regions for each site.

Group three (N= up to 300):

Addition of Group 3 which is enhanced surveillance in participants from Black, Asian or minority ethnic groups (BAME). Since the start of recruitment we have noted that only 11% of participants are from BAME population, despite recruiting in ethnically diverse regions. Given the increased risk of COVID-19 disease in the BAME community, this is a potential limitation of the study as it stands, not only because it may not reflect the diversity of the UK population, but because it does not allow assessment of whether the differing disease rates and seropositivity in adults are reflected in differences in seropositivity rates in children. Similarly to Group 2, this will recruit 0-19 year olds and will not be restricted by post code sampling.

Public Health England has an ongoing sero-prevalence programme to assess how well the population is protected from vaccine preventable diseases. The current way to check this is by testing left over blood samples from participating healthcare laboratories around the country. However, these samples may not be representative of the general population, particularly in younger age groups who are often most at risk from vaccine preventable diseases. In the Netherlands, they use a different system to assess how well the population is protected from vaccine preventable diseases, actively collecting blood samples from a representative cross section of society. This type of approach would address the limitations of using residual serum samples and allows the collection of additional relevant history e.g. number of family members and previous vaccines received. The investigators are therefore proposing a pilot study to assess the feasibility of establishing a national sero- epidemiological survey in England in individuals aged 0 - 24 years. The investigators will be focusing initially on diphtheria and group C invasive meningococcal disease, both of which are vaccine preventable. This will involve enrolling 2300 participants in the study from different geographical and socioeconomic backgrounds across our test sites and taking a blood sample. This blood will be analysed to look at the level of immunity to vaccine preventable diseases.

The original protocol has been amended to include the testing of antibodies against other infectious diseases, specifically COVID-19. A second group has been added to recruit an additional 500 to 1200 participants between the ages of 0-19 years. The additional funding has been used to open two more sites to recruit to group two across regions on England that are currently not represented by this study. Having a large number of blood samples from a range of age groups is useful when gathering information about an emerging disease such as the current novel coronavirus (COVID-19). These samples can help provide answers regarding the true number of infections with SARS-CoV-2 (the virus which causes COVID-19 disease) in this population. Group 2 can be enhanced by the samples received from other ethically approved research projects where participants have consented for their samples being used outside of the study.

Additional funding has been granted for the addition of 300 participants from the BAME community, who will form Group 3. Data from Group 3 would be invaluable in understanding whether higher rates of disease in the BAME community are a result of greater exposure to COVID-19 contact, a higher likelihood of being infected once exposed or a greater risk of disease once infection occurs.

In addition to increasing the sample size and the number of regions in the UK that are being sampled, a longitudinal sampling cohort has been introduced. A subset of participants equally distributed over the age bands will be enrolled into the longitudinal aspect of the study where repeat blood and saliva samples are taken to look for antibodies against SARS-CoV-2. A questionnaire to ascertain whether the participant or any household contacts have had any symptoms of or been tested positive for COVID-19 will also be collected.

A proportion of participants from this group from selected sites will also provide up to a maximum of three blood samples for separation of peripheral blood mononuclear cells (PBMCs) to evaluate T cell responses. These participants can be either seronegative or seropositive at their Visit 1.

With the latter addition of four more sites, all NHS regions are now represented in the study.

Inclusion Criteria:

• Parents/legal guardians or adult participant* is willing and able to give informed consent for participation in the study.
• Male or Female, aged 0 - 24 years inclusive (Group 1)
• Male or Female, aged 0 - 19 years inclusive (Group 2)
• Male or Female, aged 0 - 19 years inclusive with BAME background (Group 3)
• Parents/legal guardians or adult participants are willing to allow their General Practitioner or relevant NHS databases to be contacted for a full immunisation history

Exclusion Criteria:

• If participants do not live in the postcode districts selected by PHE (Group 1 only)
• If participants are not from the BAME population (Group 3 only
• Medically diagnosed bleeding disorder
• Medically diagnosed platelet disorder
• Anticoagulation medication
• Pregnancy
• If another member of their household is participating who is within 5 years of age of the potential participants age

Temporary exclusion criteria:

The participant may not enter the study if they or any member of their household is under temporary isolation measures for suspected SARS-CoV-2 infection.

Basic demographic characteristics will be collected by questionnaire and/or case report form (CRF) and will include: DOB, gender, GP details, ethnic group, association with communities of special interest (e.g. faith communities) household income and vaccination history.

Vaccination history will be verified during serum sample collection using the Red Book or other vaccination records, or checking with the general practitioner or the Child Health Immunisation Service (CHIS) database. Where possible this will include batch information for diphtheria pre-school booster to determine which specific product was received.