COVID-19 – should we be concerned about high case numbers?

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Scotland has witnessed record COVID-19 infections over the last week. Despite this, the Scottish Government is still planning to lift remaining restrictions by 9 August. So why the lack of alarm?

Scottish Government approach to the pandemic

Until now, the Scottish Government’s approach to the pandemic has been aimed at suppressing case numbers. However, case numbers were never really the main concern. They were merely a proxy for hospitalisations and deaths.

During the first and second waves of the pandemic, there was a fairly straightforward relationship between infections, severe illness and deaths, with scientists assuming a two-three week lag for infection numbers to filter through. A surge in cases meant pressure on the NHS and people dying.

Has this changed now that the vaccination programme is underway?

In the wake of case numbers rising recently, the First Minister announced to the Scottish Parliament that the aim had changed from suppressing the virus to the lowest level possible, to suppressing it ‘to a level consistent with alleviating its harms’. This is a significant change in approach.

Link between case numbers, illness and deaths

Data from Public Health England provides reassurance that the most common strain of the virus currently in circulation (Delta) is resulting in fewer hospital admissions and deaths than some of its predecessors, most notably, the Alpha variant (sometimes referred to as the Kent variant).

This is shown in the figure below which illustrates the proportion of attendances at emergency care with the alpha or delta variants which then resulted in an admission or death.

Case numbers started rising again in Scotland at the start of May and have hit record levels over the last week. However, the following chart shows that, as yet, the same growth has not been seen in hospitalisations, ICU admissions or deaths. They have risen, but at nowhere near the same rate as infections.

The previous peak in confirmed cases was on 7 January 2021, when they reached 2,649 in one day. The resulting peak in deaths occurred in the week beginning 18 January, with 452 weekly deaths involving COVID-19.

Compare that to the most recent weekly death figure of 17, shortly before cases reached a record 4,234, and it does seem like we may be in different territory.

This is reflected in public statements from the Scottish Government and its officials, who are now much more certain that the link has at least been weakened.

The updated strategic framework also highlights that more cases are occurring in younger people – who are at less risk of severe disease – and those who are admitted to hospital have a shorter length of stay.

However, some are now questioning whether we should be lifting restrictions at a time when infections are so high. The reasoning behind this includes:

  • the vaccine is not 100% effective
  • a significant proportion of people will not be vaccinated
  • mutations and length of immunity
  • the long term effects of COVID
  • the harmful effect of restrictions.

These issues are explored in more detail below.

Vaccine effectiveness

Of the three vaccines being rolled out in the UK, none of them are 100% effective in reducing infections, onward transmission, or the risk of hospitalisation and death.

The following table shows the assumptions on effectiveness that the Scottish Government uses in its modelling, broken down by vaccine type:

Vaccine
Reduction in risk of infection
Reduction in risk of hospitalisation or death
Pfizer/BioNTech – 1st dose
65%
91%
Pfizer/BioNTech – 2nd dose
70%
95%
Oxford/AstraZ – 1st dose
65%
88%
Oxford/AstraZ – 2nd dose
70%
93%
Moderna – 1st dose
65%
90%
Moderna – 2nd dose
70%
95%
Scottish Government Vaccine Effectiveness Assumptions – Source: SAGE papers from SPI-M-O

This shows that the Scottish Government expects fully vaccinated people will still have a 30% risk of infection if exposed, but those who become infected will have their risk of hospitalisation or death reduced by 93-95%.

The updated strategic framework notes that the proportion of positive cases ending up in hospital has fallen from a peak of over 14% in January to less than 4% in June.

Unvaccinated population

The UK and Scottish Governments have paused the easing of restrictions while they try to vaccinate as many people as possible. However, there will always be a proportion of the population who will be unvaccinated, but what size that proportion will be is uncertain.

Population coverage with the vaccine is important for achieving “herd immunity”. Herd immunity has become a loaded term, but it simply refers to the proportion of a population who need to be immune (either through a vaccine or previous infection) to stop widespread community transmission.

The level of coverage required is directly linked to the transmissibility of the virus. The more infectious the virus, the greater the coverage required.

The Delta variant is believed to be more transmissible than its predecessors with estimates that we would need to achieve 80-90% coverage to achieve herd immunity.

It is unlikely that this will be possible without vaccinating under 18s and, if not, it raises questions as to how ethical that would be. This is because children and young people are at less risk of the disease therefore you could effectively be vaccinating them for the benefit of others.

The Joint Committee on Vaccination and Immunisation (JCVI) has not issued its advice on vaccinating under 18s yet but – to date – its strategy has been aimed at protecting those at higher risk of disease rather than trying to limit transmission. It will be interesting to see if this changes.

Mutations and length of immunity

Even if we assume that the link with severe illness and death has been weakened, widespread transmission may increase the risk of new variants emerging.

So far the vaccines seem to be holding up well to the strains in circulation. However, the virus is always changing and high case numbers coinciding with not everyone being vaccinated gives new variants the opportunity to gain a foothold.

There is now increasing concern about the Lambda variant which has emerged from Peru and is already in the UK. It is a ‘variant under investigation’ and believed to be highly transmissible but we do not know if the approved vaccines offer protection against it or if it has a higher mortality rate.

Immunity is being monitored by the SIREN project which tests a cohort of NHS workers who were either previously infected or have vaccine induced immunity. The frequency of PCR positivity in the SIREN cohort overall has increased in June, after very low levels March-May, but remains low.

Long-COVID and chronic health conditions

It has also been argued that we should not be complacent about high infection rates until we fully understand the long-term implications of COVID-19.

Long COVID is already causing concern, with an estimated 89,000 people in Scotland experiencing a wide range of symptoms of varying severity. However, there is also growing evidence that it may lead to multi-organ damage and cause chronic diseases such as diabetes and lung disease, even in those who had mild or moderate symptoms.

Effect of the restrictions

One final area of concern relates not to the high number of infections themselves, but the associated restrictions.

Restrictions aim to minimise harm, but it is widely recognised that they cause their own harms.

The guidance on self-isolation has not changed since the vaccination programme was rolled out. As a result, the recent increase in cases has been accompanied by an increase in COVID-related staff absences in the NHS as more people are required to self-isolate.

The majority of these absences are in nursing and midwifery staff and so, although demand for hospital and ICU beds may not have increased drastically, the lack of staff makes it harder to meet current demand.

This is highlighted in the recent reports of Raigmore hospital in Inverness being placed in ‘code black status’ due to large numbers of staff having to self-isolate.

However, the strategic framework does hint that this may be an area for change:

Evidence is emerging that the vaccination programme is having an effect on the link between infection and hospitalisations. As this evidence base develops, we will continue to review whether existing self-isolation requirements remain necessary and appropriate.

Conclusion

There is encouraging evidence that we do not need to be quite so concerned about the record case numbers of recent days. However, a number of uncertainties remain and hospital cases and deaths are still rising. What level is tolerable is likely to be the subject of much debate as restrictions are lifted.

Kathleen Robson, Senior Researcher