ITV News Meridian's Penny Silvester reports.
People in the south are being urged to donate plasma, as the NHS says the number of donors is far behind target.
The Reading Donor Centre is only around 40% full each day, with around 140 appointments going empty every week.
Plasma is used to make lifesaving medicines - including antibody medicine.
This medicine, known as immunoglobulin, is used to strengthen or stabilise the immune systems of people with rare or life-threatening diseases.
Aiden Davis is one of the thousands who has benefited from access to lifesaving plasma medicines as a new born baby.
Aiden was born at Winchester Hospital in April 2019 but immediately transferred to the Neonatal Intensive Care Unit at Southampton Hospital for emergency care.
His mum's blood had crossed the placenta and reacting his against his own blood, destroying his red cells.
Mum Steph Davis, 38, a teacher from Eastleigh, said: "They said he was at risk of jaundice so they would keep him in overnight.
"They found his bilirubin level - a pigment showing the breakdown of red blood cells - was more than 90 times the normal.
"At that point they realised there was a battle going on his blood.
"They did further tests and we were told the only way he could survive was with a full blood exchange.
"He was newborn, I'd only held him a couple of times, and within a few hours was told this is the only way to save him."
Steph said: "I am forever grateful to the people who donated the blood.
"I am now a registered donor myself and actively promote and encourage blood donation as much as I can, especially around the time of Aiden's birthday each year.
"You take it for granted there will be blood there and that it will be compatible for your needs, and if it hadn't been there, we wouldn't have Aiden now."
She said of plasma donation and IVIG: "Plasma donation is really important as it can contribute to saving people's lives.
"Sometimes it's not until you are faced with a life or death situation that you really truly appreciate how incredible the people are who have been able to make a blood or platelet donation.
"Two weeks ago we got to celebrate Aiden's 2nd birthday and we know that it's thanks to a very thoughtful, selfless stranger (and a team of incredible consultants, doctors and nurses) that he is here with us today and we have been able to enjoy two wonderful years of him so far."
Last year, 704 people in Southampton and Hampshire received plasma medicines, 434 in Kent and the Medway, 555 in Sussex and Surrey, and 750 in the Thames Valley.
Paula Ussher, Reading Donor Centre Manager, said: "Plasma is a powerful, lifesaving part of your blood, which can be used to make unique, lifesaving medicines.
"Since donation restarted we've had many fantastic people come in to donate but we still see too many empty chairs every day.
"In the next few months, we need thousands more people to start donating at our donor centre."
The NHS has launched a campaign to drive up numbers, which includes adverts across social media and in public places.