‘Immune memory’

“Individual variations in immune response, influenced by age, genetics and underlying health conditions, play a significant role in varying Covid symptoms,” Dr Simon Theobalds, a GP at Pall Mall Medical, tells Stylist.

Generally, the more immunity people build up to a virus from vaccinations or infections, the milder their symptoms of subsequent infections tend to be. However, as Dr Ziyad Al-Aly, the chief of research and education services at the VA St. Louis Health Care System, tells the New York Times: “Anything from developing new medical conditions or ageing can affect how sick you get.” He even notes that small variations in our microbiome health can alter how we respond to an infection at one time or another.

We all have our own individual ‘immune memory’, explains Dr Theobalds. This is created from previous infections or vaccinations and it will affect how symptoms manifest themselves when we catch Covid.

Multiple organs

Covid is a complex virus that can affect huge areas of our body, which is another reason medics and scientists believe symptoms can vary so widely.

“The virus has the ability to infect multiple organs, such as the lungs, heart and nervous system,” says Dr Theobalds. “This leads to diverse clinical presentations.”

Why do Covid infections feel so different every time?