Johnson & Johnson is the second company to hit the pause button for a COVID-19 vaccine phase 3 trial.

This trial aims to recruit 60,000 participants, one of whom developed “an unexplained illness.” A study pause by the company is standard protocol in these cases.

According to a release issued by Johnson & Johnson, the patient’s illness is being reviewed by the trial’s independent Data Safety Monitoring Board, as well as the company’s clinical and safety physicians.

“ Adverse events – illnesses, accidents, etc. - even those that are serious - are an expected part of any clinical study, especially large studies," the release said.

The company is not releasing any information about the patient and the illness that caused the temporary hold. Because the study is a randomized, double-blind, placebo-controlled trial, neither the participant nor the investigators who administered the vaccine know if the participant received the actual vaccine or a placebo. This will be part of the investigation.

In early September, AstraZeneca also put a trial on hold as the company investigated a participant’s illness. The J&J vaccine and the AstraZeneca vaccine have two things in common. Both vaccines are based on what's called an adenovirus, which instructs cells to manufacture the necessary vaccine proteins. They also are part of the U.S. government's Operation Warp Speed, the public-private cooperative effort to get a vaccine approved and distributed. Warp Speed has been heavily criticized recently after an NPR investigation showed that at least $6 billion in US funding was awarded to various pharma companies, including J&J, through a third-party, a defense contract management firm. This side-step of the established acquisitions process, which details how federal contracts are to be awarded, allows the awarding process to be kept under wraps.

Related article: AstraZeneca Pauses COVID-19 Vaccine Trial Due to Volunteer's Illness

The AZ trial has since resumed in all participating countries, except the United States. According to STAT, this has caused concern among some American study participants. They received their first dose of the 2-dose vaccine candidate, but cannot get the follow-up injection until the trial is restarted. The Johnson and Johnson vaccine candidate is a single-dose vaccine.