Public Health England data compares the number of deaths registered with how many were predicted based on previous mortality rates to calculate the number of excess deaths in an area.
Based on estimates for 2015-19, West Sussex was predicted to see 4,966 deaths from any causes in the first 26 weeks of the year (January 2 and July 2).
But there were 5,274 deaths during this period – 308 more than were estimated.
Of the deaths registered in the first half of 2021, 1,023 (19 per cent) had Covid-19 on the death certificate.
Excess deaths are considered a better measure of the overall impact of Covid-19 than simply looking at mortality directly linked to the virus, as they capture deaths that may have been indirectly caused by the crisis.
Across England, there were 29,700 excess deaths during the first eight weeks of the year, as the effects of the second coronavirus wave were felt.
But between March and the start of July, there were 10,700 fewer deaths than expected.
The King’s Fund said Covid-19 may have caused the premature deaths of some people, particularly the elderly, who would have died of other causes in the weeks and months following the peak periods of the pandemic.
It added that the number of excess deaths has followed the waves of Covid-19 infections rather than any seasonal trends as is usually the case.
Dr Veena Raleigh, senior fellow at the think tank, said: “Compared with the 2015-19 average, the waves of high excess deaths in both 2020 and 2021 have been followed by a fall in deaths.
“In total, there were more excess deaths in the second wave than the first wave of the pandemic, which may explain why there is a bigger deficit in deaths between March and July 2021.”
The week ending February 5 was the deadliest of the first half of 2021 in England, when there were 5,004 excess deaths.
This was also the week that West Sussex had its highest excess death total in the first six months of 2021, when the area recorded 120 excess deaths.
By contrast, there were 44 fewer deaths in the week ending July 2 than had been predicted.
Of the first 26 weeks of the year, there were 11 when registered deaths surpassed the estimate and 15 when the death toll fell below this point.
Sarah Scobie, deputy director of research at the Nuffield Trust, said England has seen fewer deaths from other illnesses such as flu this year because of social distancing and lockdowns.
She added: “Case numbers are beginning to fall again, but excess deaths for this time of year against the average have been creeping up.
“This rise is in line with the recent case rise over the last few weeks, but thanks to the vaccine effect, not as rapidly as cases, or in line with previous waves.”