London Barndance: COVID-19 Risk Assessment
Risk assessment 06/04/2023
Statistical background
The ONS Coronavirus (COVID-19) Infection Survey provided a reliable analysis of the prevalance of the disease across the UK. It was discontinued in March 2023 so we will now only update this risk assessment if significant new information becomes available. In the year March 2022 - March 2023 COVID-19 prevalence ranged from 1.5% to 8% of the population in England.
COVID-19 is almost certain to be present at all our events
With so many people now infected and the symptoms often being very mild we must now assume that one or more infected people will be present at all events. In fact it is quite likely that there will be more than one infected person in the room.
For the full details see our Covid-19 risk calculations spreadsheet - also available with example numbers in PDF.
Free test distribution ended some time ago so we have to assume that most people will not test themselves even if they have symptoms.
Available Mitigations
We must assume that several infected people will attend. This situation is likely to continue for the forseeable future.
Clinically vulnerable people will be advised not to attend.
We will continue to make full use of the ventilation system in the hall.
Dancers will be advised to wear FFP3 masks if they are concerned for their own health, but this does restrict breathing so we cannot advise it for everyone.
The ultimate line of defence is vaccination. Research shows that fully-vaccinated (2+ doses and reccommended boosters) people are very unlikely to need hospitalisation if they catch any COVID-19 variant. We will strongly advise people to stay at home if they do not have this level of protection.
Risk assessment below this line was updated 07/12/2021
The Covid-19 situation changed significantly with the arrival of the Omicron variant at the end of 2021. Some of the assumptions and conclusions that we made in 2021 are no longer valid. The December 2021 risk assessment is reproduced below as some of it is still useful although the numbers should be ignored.
See also: Cecil Sharp House Covid Secure page
Background
(Authoritative references have been added to back up some of these statements)
There are no legal restrictions on events at the moment. We will check the legal and health situation about a week before each event and post updates on the website if necessary.
COVID-19 is primarily spread by aerosols and droplets. This suggests that we should focus safety measures on that infection route rather than touch-based routes.
There are two main sources for information on how many people are infected: NHS Test & Trace, and the Office for National Statistics. The two sets of data cannot be directly compared
Case numbers for 6/12/2021 from Test and Trace show about 300-600 new cases per 100,000 per week in our catchment area. This is the number that tends to get reported in the press as it is updated daily, but it does not show how many people are actually infected on a given day.
ONS surveys show that about 1.6% of Londoners and 1.7% of people in the wider South East were infected on any given day in the week ending 27th November 2021. At that time, children of school age were much more likely to be infected (3.5% - 4.2%) than adults (0.5% - 1.2%). - Our audience is predominantly over the age of 18, so we could use a figure of around 1.5% if we count children as equivalent to four adults each.
We need to estimte how many infectious people might be present at one of our events. The audience in 'normal times' ranges from 80-130 people. We expect smaller numbers for the dances in 2021 so basing the calculation on 100 people seems reasonable. (In practice the number so far have been under 80 so this is conservative).
People are most infectious a day or two before they show symptoms and continue to be infectious for about another 7-10 days. There are some asymptomatic cases - at one time this was thought to be the majority but more recent work published in BMJ suggests a range of 17% to 20%. The same paper suggests that truly asymptomatic cases are 3-25 times less infectious than symptomatic or pre-symptomatic cases so taking these numbers together we can ignore asymptomatic cases in our calculation because other uncertainties are very much larger.
Very few people will go out socially if feeling ill (and we will specifically ask them not to) so the risk comes mainly from pre-symptomatic and untested mild-symptom cases. It seems reasonable to assume that on catching COVID-19, each person carries on as normal for the first 3 days of their infectious period and then continues to test positive (as defined by ONS) for a further 7 days while isolating. Taking this with a 1.5% infection rate for our target audience suggests that of 100 people we would expect 0.5 infected cases (i.e. one active case every other event).
The actual numbers will vary as the pandemic progresses, but for planning purposes it seems that we should assume that a very small number (1-2) of infected people might be present at each event.
The probability of catching COVID-19 from an infected person
This is referred to as the Secondary Attack Rate (SAR) in the literature. It depends on the setting and the duration of exposure.
Some numbers are available that we could use to estimate SAR for a contra dance event. The MRC/Imperial College Report 38 - SARS-CoV-2 setting-specific transmission rates: a systematic review and meta-analysis provides an overview of the available data, showing that SAR ranges from about 1.2% for casual close contacts to about 21% within households (see in particular Table 1 of the full paper). Within this range, 'social gatherings with family and friends' comes out around 6% (the 95% confidence interval is from 3.8% to 8.1%, reflecting the wide range of settings that this can cover in a global study). The data relates to studies done before vaccines were available, and the gatherings described were mainly indoors where the index case would have remained close to the same people for several hours. It would be reasonable to expect that dancers in a well ventilated hall would experience a SAR above the 'casual close contacts' rate and below the 'family and friends' rate.
Vaccines used in the UK have at least 60% efficacy after a single dose, rising to 90% or more after the second dose. On top of that they provide a reduced risk of hospitalisation in people who do catch COVID-19. If we assume unvaccinated SAR to be between 1.2% and 6% for our setting then if everyone is fully vaccinated we should see SAR drop to the range 0.12% to 0.6%. For people who have only received the first dose the range would be 0.48% to 2.4%. Vaccine rollout is now well advanced, and it is reasonable to assume that at least 80% of our likely audience is fully vaccinated. We make it clear that we are assuming that everyone is vaccinated for their own protection.
Assuming that we have one active case and 100 attendees at each event, this suggests that less than one person will become infected as a result of attending.
Another way of looking at the transmission risk is to use the same rules as the NHS COVID-19 app. This requires 15 minutes or more within 2m of an infected person before it registers a risk of infection. A typical contra dance runs for about 5 minutes and most people then change partners, so they would never reach this threshold.
Face masks can cut transmission risk, but are most effective when worn by the infected person. As mask use in general is declining, it is not reasonable to assume that all infected people will wear masks. Dancing is an aerobic and social activity, so masks are not desirable to most people even if they would happily wear one in a shop. People who are at greater risk if they catch COVID-19 might want to consider using masks certified to the FFP3 or FFP2 standard, as FFP3 in particular has been shown to be very effective in this role: https://www.cam.ac.uk/research/news/upgrading-ppe-for-staff-working-on-covid-19-wards-cut-hospital-acquired-infections-dramatically
UK vaccine rollout is well advanced, but has slowed considerably. We cannot realistically verify the vaccine status of our audience, but we can strongly suggest that vaccination is desirable.
Consequences of catching COVID-19
For most people, COVID-19 is a mild illness, and for many the symptoms will ease within 10 days.
It can be more serious for older people and for those with some types of underlying illness.
There has been much press discussion of 'Long COVID' and this is clearly an issue of national proportions, but the vast majority of people are expected to recover from COVID-19 without any long-term effects.
In all cases vaccination has been shown to reduce the risks considerably but particularly vulnerable people should continue to be cautious.
Specific risks and mitigations
Risk: group event with people coming from far and wide
Mitigations:
- Group size: our events normally attract about 130 people, so at late-2021 peak infection rates we would expect to have one infected dancer every other event.
- Vaccine: We will strongly encourage people to get vaccinated before coming to our events as vaccination reduces the risk of catching COVID-19 by a large factor and reduces the risk of severe disease by a very large factor. It also reduces the risk of onward transmission by an infected person by about 40%.
- Testing: we will ask that people use a lateral-flow test before coming to our events.
- Registration: people will be asked to scan the NHS QR code or to leave contact details in case an infection is confirmed. This is less important for vaccinated people, as from 16th August the UK Government does not require vaccinated contacts of active cases to self-isolate.
Risk: aerosol/droplet transmission
Mitigations:
- Ventilation: Kennedy Hall has forced-air ventilation that can be set to draw air entirely from outside. When heating is required much of the air is recirculated through HEPA filters. We are not allowed to open the external doors while music is being played, so we will make sure that the fans are always on. [ For those who know the venue: the air-handling equipment was replaced recently and is much better than you probably remember! ]
- Space: Kennedy Hall has a nominal capacity of 400 people. We will be operating with much smaller numbers - probably well under 100 in 2021. The hall is 21m x 12m, so with 100 people each would have 2.5 square metres - obviously dancers will be organised into sets rather than spread uniformly so some people will be closer together. The ceiling is high (about 6m) so aerosol dilution will be good even if air is recirculated (15 cubic metres of space per person).
- In Contra dance you tend to be within 2m of your chosen partner much of the time, and your partner's mouth will be less than 1m from yours in some moves. The dances are progressive though, moving on to meet another couple at 30s intervals, so you are likely to spend less than one minute at a time near any other specific person. That suggests that if we have one infected dancer they are unlikely to be able to infect people other than their chosen partners (between 1 and 10 people depending on who it is and whether they stick to the same partner all evening). We will suggest that particularly vulnerable people limit the number of different partners they take during the evening to further reduce the chance of them spending time near an infected person.
Risk: people with specific vulnerabilities - We know that some members of bands and audience have respiratory issues.
Mitigations:
- Band members are normally several metres from the nearest dancers.
- Vulnerable people will be advised to wear masks to FFP2/FFP3 standard when near other people.
- Vulnerable people will be advised to limit the number of different partners they take during the evening.
- There will be an area of the dance-floor designated for 'more distant' dancing, so vulnerable people can avoid being close to other people.
- Some moves (particularly the swing) bring dancers close together. In 2021 we will ask callers to avoid dances where people swing anyone other than their chosen partner. This allows them to agree in advance to use a more distant form of the move (e.g. cross-hands swing rather than ballroom-hold).
Risk: touch-based transmission
Dancers touch the hands of most other people in the set, and also touch waist and shoulders of partners and neighbouring dancers. If this transfers virus particles there is a risk of infection when the receiving person touches their own eyes nose or mouth.
Mitigations:
- The venue provides hand-wash facilites and hand-gel
- People will be advised to bring their own hand-gel and to use it particularly before touching their face.
- There was a lot of focus on touch in the early stages of the pandemic, but more recent (2021) research suggests that touch is a relatively minor factor in transmission of COVID-19.
Summary
We are likely to get one or two COVID-infected people at some of our events. With the mitigations listed above and assuming the vast majority of the audience is vaccinated, it is unlikely that even one more person will become infected as a result of attending.