Long Covid is where symptoms arising from Covid are prolonged, typically regarded as more than 4 weeks or 12 weeks. Sometimes more than a year. The symptoms are described in various ways, and can include new symptoms where the virus has spread around the body due to its ability to attack other organs such as the heart and brain.
Some people find the symptoms debilitating, preventing them from working properly or indeed at all. Long Covid can be serious.
What about Long Covid arising from the Delta variant, which we can term Long Delta?
This last Friday the UK’s Office for National Statistics (ONS) published a report setting out three approaches to estimating Long Covid. That was through fieldwork up to 1 August, effectively the end of July. That covers two months of Delta dominance, mixed with data for the previous dominant variant Beta. Nonetheless we can begin to see the impact of ‘Long Delta’ in the 4-week data.
WHAT ARE THE CHANCES OF LONG COVID?
The ONS's CoronaVirus (COVID-19) Infection Survey (CIS) regularly tests a broad sample of people for COVID-19 using PCR tests. One approach to assess Long Covid was to follow up around 25,000 people who had tested positive to track their symptoms by comparison against the same number of equivalent ‘control’ people who had tested negative. Controls are the same age, sex etc, and aim to represent the general uninfected population.
The ONS gives a number of caveats as to the reliability of the data, given the difficulty in defining and proving Long Covid. But the data can be regarded as indicative.
WHAT ABOUT SYMPTOMS LASTING MORE THAN 4 WEEKS?
Let’s compare people with symptoms lasting more than 4 weeks. comparing incidence of people with tested positive with the controls tested negative, and ignoring severity of the symptoms. We see from the data in Table 1 of the report, by taking these differences as the chances of Long Covid:
- Younger people aged 2 to say 30 are some 2% likely to suffer Long Covid more than for 4 weeks, around 1 in 50
- This quickly rises for the over 30s to some 6-8%, or 1 in 14
- Females are 2% higher than males on average
- Prior health conditions double the chance. Conversely no health conditions only halve the chance.
WHAT ABOUT LONG DELTA?
The 4-week figures above are influenced by Delta, but are not just Delta. ONS has not attempted to assign the data to variants.
However we know that Delta is more transmissible than earlier variants which means:
- People are infected by a lower ‘viral dose’
- Once infected, the infection grows to a higher ‘viral load’
- That means a higher risk of serious illness and hospitalisation, which we know to be the case
- And PCR tests will need fewer number of cycles to confirm an infection.
- Likely to result in higher incidence and severity of Long Covid
The ONS study has confirmed that a low cycle threshold under 29 results in a nearly 3% increase over the average.
We might conclude that the chances of 'Long Delta' for people catching Delta are higher than the ONS figures, say:
- Under 30s of over 3%, more than 1 in 33
- Over 30s of over 9%, more than 1 in 11
WHAT ABOUT OVER 12 WEEKS?
Table 1 suggests for symptoms over 12 weeks, being based primarily on Beta infections, and ignoring any change in severity:
- Around half the people over 30 who had symptoms after 4 weeks will not have any symptoms after 12 weeks, but half will continue with symptoms
- People under 30 who have symptoms after 4 weeks will typically still have symptoms after 12 weeks
- The drop in rates for the control group suggests Long Covid can happen even for those with a negative PCR, who may nonetheless have been fighting off COVID-19. This may help to explain why the control group symptoms are not zero, and that Long Covid may still arise for people officially uninfected
WHAT ABOUT SEVERITY?
The ONS acknowledge that symptoms can be debilitating, making work difficult or impossible, but have not included any relevant data in the report.
WHAT DIFFERENCE DOES VACCINATION MAKE?
No account is made in the report of the impact of vaccination status. Vaccinations were ramping up during the fieldwork period, so the data represents a part-vaccinated population. Older people were more likely to have been vaccinated than younger people by end July, but few would have been vaccinated when tested positive weeks or months earlier.
We know vaccination reduces the chance of serious disease, so therefore likely to reduce the incidence of Long Covid. The figures above should reduce for those people exposed to Delta after vaccination.
IN CONCLUSION
Indicatively, we can conclude that:
- For the unvaccinated:
- More than around 1 in 33 of the under 30s will suffer from Long Delta for at least 4 weeks, and typically more than 12 weeks
- More than around 1 in 11 of the over 30s will suffer from Long Delta for at least 4 weeks, dropping to 1 in 22 after 12 weeks
- Females have a 2% higher chance than males
- Those without a prior medical condition are still around half as likely as those with
- Vaccination should improve the odds, but the report covers a period too early to say
- We need better data on serious, debilitating symptoms
- We also need to know the odds for infections only after 1 June, when Delta was dominant
With around 30,000 new confirmed cases a day in the UK at present, mainly in those unvaccinated, these odds mean thousands of people a day suffering long-term symptoms. That's not just those suffering, but this inevitably puts an additional strain on GPs who will be consulted, and the specialist services to which people will then be referred. So the strain on the NHS is not just those hospitalised.
Overall the risk of Long Delta to individuals and the NHS is yet another reason for everyone to get vaccinated.
