Displaced mortality, where deaths that would have occurred later in the year happened earlier for an unusual reason, could be the reason why the excess number of deaths has dropped below the five-year average for the fifth consecutive week, say experts.
Excess deaths compare the number of deaths in a given week and the five-year average for that week. They are considered the most reliable measure of the impact of Covid-19.
There have now been almost 58,000 excess deaths since the first deaths due to Covid-19 were reported in England and Wales, ONS data shows.
At the height of the pandemic, deaths were consistently above average, and for two weeks in April reached double their usual number.
However, as the first wave of Covid deaths has declined, the trend has appeared in the reverse, with lower than average deaths reported for five weeks in a row.
The number of deaths registered was 3% below the five-year average in the week ending 17 July (week 29) the figures show. In that week the number of deaths attributed to Covid-19 dropped to 295 deaths – the lowest death toll reported for 17 weeks. Experts say that this could be due to “displaced mortality”.
Sarah Caul, head of mortality at the ONS, said: “It could be that we’re seeing a dip below average because people died earlier than they would have usually, because we saw such a big excess [earlier in the pandemic].
“Because Covid particularly affects the most vulnerable, those who were potentially likely to die during this current period may have already died.”
More than nine in 10 patients who died from Covid-19 were aged over 60, analysis of ONS figures shows. Data from NHS England shows that a similar proportion of those who died in hospital had an existing health condition before infection.
In a blog post for the ONS, Caul also wrote that longer-term mortality trends might be causing this discrepancy.
“Another reason why the number of deaths may continue to fall below the average is due to the fall in the number of deaths experienced in recent periods before the start of the pandemic.
“The number of deaths registered in 2019 was 2% lower than 2018, and as mentioned earlier, we saw the number of death registrations fall below average for the start of 2020. Deaths falling below average could be a continuation of this trend.”
The ONS issued a note of caution over fatality figures for recent weeks, because the figures could be revised subsequently due to a lag in death registrations.
Therefore the full impact of lockdown on health remains uncertain, particularly in the case of deaths due to suicide or substance abuse, which can take a long time to confirm.