The Therapeutic Goods Administration will publish its own findings into CSL flu shot irregularities in the wake of an investigation by US authorities in April and a follow-up letter accusing the company of failing to properly probe “dark particles” in its vials.

The US Food and Drug Administration’s two audits of CSL’s Parkville premises in April, which have been ignored by the Australian media despite stories appearing in the US business press and specialist publications this week, was followed up by a “please explain” letter sent on June 24 to CSL’s CEO Brian McNamee, the brother of tennis legend Paul McNamee. The letter was publically released this week on the FDA’s website alongside with an explanatory note on the reasons behind the probe.

It criticised the firm for not accounting for the possibility of a chemical reaction between the vaccine preservative and vials or rubber stoppers used to plug the flu shot containers, but said the vials had not endangered any patients. The investigation did not relate to the single dose syringes that were the subject of a recent seizure scare in Western Australia.

But until this morning the TGA had remained mute in line with the tight control it exercises over the information flow from Canberra. The TGA closely collaborated with the FDA during the probe and maintains strong links with the formerly government-owned manufacturer.

The TGA told Crikey it had “contributed detailed information to the public statements on the investigation of the flu vaccine issue made by the Chief Medical Officer”, and will soon publish on its website a summary of the findings:

“The TGA is aware that the US FDA’s Centre for Biologics Evaluation and Research  published an Untitled letter addressed to CSL Ltd citing deviations in the facility’s compliance with current Good Manufacturing Practices. This type of letter is a standard US regulatory practice whenever matters are identified during a manufacturing inspection. It relates to products supplied to the United States.”

However, it remains unclear whether the TGA had identified the problems with the CSL vaccine before its tenacious US counterpart raised the alarm.

“Importantly,” the local regulator said, “these findings do not relate to the single dose flu vaccine vials that have been associated with febrile convulsions in Australia.” The use of seasonal influenza vaccines were suspended for children under five after troubling reports of fevers, seizures and convulsions.

The FDA’s letter demanded follow-up meetings with McNamee to ensure his product remained legit: “We would like to meet with you and other senior management at CSL Biotherapies to further discuss the issues cited in this letter and how you will address them going forward. Given the potential contributions of safe, pure, and potent vaccines to the public health, we encourage frequent interactions between your technical staff and FDA in an effort to help CSL Biotherapies move forward with corrective actions as rapidly as possible.”

The FDA also told the company to ensure containers don’t react or leach into the product, that batches of vaccines are examined each year for deterioration, and to establish tests to assure the regulator they conform to standards of strength, quality and purity.

A CSL spokesperson said this week the company was taking the issues raised by the FDA “very seriously”.

“Our investigations show that the particles are a discoloration of the vaccine, and are not foreign-contaminating matter,” they said. “CSL … will work with the regulator to resolve its concerns.”

CSL shares fell 0.68% or 32 cents to $32.51 this week, outperforming the broader market which tumbled 5.1%.