Strep A is surging in the UK and has already killed at least 19 children. Here's why it's taken so long to make a vaccine against this deadly pathogen.

• Strep A is surging in the UK and has killed at least 19 kids, the UK Health Security Agency said.
• The disease, which can lead to serious complications, can often be treated with antibiotics.

A surge of group-A streptococcal infections, or strep-A infections, is causing concern in the UK. As of December 15, at least 19 child deaths had been reported by the UK Health Security Agency.

These numbers are unusual — this is the largest surge of severe strep A in years. It's unclear why this large of a surge is happening, though the lifting of pandemic restrictions may be playing a part.

Some researchers have hypothesized that during lockdown periods, children weren't exposed to strep A, so they did not develop any immune resistance to the disease. This theory has not been proved.

The US Centers for Disease Control and Prevention is also investigating a whether there's been an increase in severe strep-A cases in its country. It advises parents to be on the lookout for severe symptoms and to make sure their children are keeping up with their flu and chickenpox vaccines.

Strep A usually causes a sore throat and sometimes a skin rash. If it becomes advanced enough, in rare cases, it can lead to complications including scarlet fever, rheumatic heart disease, necrotizing fasciitis, and streptococcal toxic-shock syndrome, which can be fatal.

According to the Strep A Vaccine Global Consortium, strep results in an estimated 500,000 annual deaths, many of which are in countries whose residents bring in middle and lower income. Of these deaths, 350,000 are attributed to rheumatic heart disease caused by strep A, while 150,000 are caused by acute infection.

Researchers have been trying to make a strep-A vaccine for decades

If it's caught in time, strep A can be treated with antibiotics. But what is perhaps needed is a vaccine that can prevent infection.

Vaccine development has been in progress for decades. One of the first attempts was in 1946, but it had a lot of side effects and didn't protect against infection. There's a vaccine that protects against different but related bacteria, streptococcus pneumonia.

But strep A is difficult to vaccinate against for a few reasons: There's a lot of variation in parts of the bacteria to target, vaccines need to be safe and not trigger any autoimmune responses, and animal models aren't ideal for studying how strep-A infection works. Additionally, there has not been a significant monetary incentive for companies to attempt to develop a vaccine.

There is no vaccine commercially available, but several research groups are working on developing one. Candidates are in trials, but these are all early-stage or preclinical trials — meaning it will likely be several more years until any of them are available to the public.

Many of the research groups working on a strep-A vaccine have hit roadblocks

One of the groups furthest along in developing a strep-A vaccine is made up of researchers from the University of Tennessee and Dalhousie University in Nova Scotia. The group developed a vaccine candidate called StreptAnova and published a phase-one trial in 2011. It has also completed some early safety trials.

But James Dale, one of the main developers of StreptAnova and a primary author of the study, told Insider there had been no progress since that first trial.

"There has not been any interest from pharma or the vaccine industry in supporting further clinical development," he told Insider in an email. "Until we have substantial financial support, StreptAnova remains an 'impeded' vaccine."

Researchers at the Queensland Institute of Medical Research also completed a phase-one trial, in 2018, with 10 adult participants. Those researchers did not respond to a request for comment about whether their vaccine was still in development.

The most recent strep-A vaccine candidate comes from two groups at the University of Alberta and Griffith University, which began a phase-one trial with 20 participants in late November. They hope to train the immune system to identify a protein that's a fusion of two common proteins on the strep-A bacteria so the vaccine will be effective against a wide variety of strains in the strep group.

A GSK spokesperson confirmed to Insider that it's also in the early stages of developing a strep-A vaccine but that it had not started human testing.

"We are hopeful that our experience of developing innovative vaccines for pathogens for which vaccines have not previously existed, and technological advances in vaccinology, could lead to a successful Strep A vaccine in the coming years," a company spokesperson said.