The reasons for the disease being milder in vaccinated people could be because vaccines, if they don’t block infection, seem to lead to infected people having fewer virus particles in their body.

COVID-19 vaccines and prior coronavirus infections can provide broad immunity against other, similar coronavirus es, according to a study.

The findings, published in the Journal of Clinical Investigation, build a rationale for universal coronavirus vaccines that could prove useful in the face of future epidemics.

“Until our study, what hasn’t been clear is if you get exposed to one coronavirus , could you have cross-protection across other coronavirus es? And we showed that is the case,” said study lead author Pablo Penaloza-MacMaster, assistant professor at Northwestern University Feinberg School of Medicine, US.

The three main families of coronavirus es that cause human disease include Sarbecovirus, which includes the SARS-CoV-1 strain responsible for the 2003 outbreak of Severe Acute Respiratory Syndrome (SARS), as well as SARS-CoV-2, which causes COVID-19 .

The other two are Embecovirus, which includes OC43, often responsible for the common cold, and Merbecovirus, which is the virus responsible for Middle East Respiratory Syndrome (MERS), first reported in 2012.

The study found that plasma from humans who had been vaccinated against SARS-CoV-2 produced antibodies that were cross-reactive, or provided protection, against SARS-CoV-1 and the common cold coronavirus (OC43).

The researchers found that mice immunised with a SARS-CoV-1 vaccine developed in 2004 generated immune responses that protected them from intranasal exposure by SARS-CoV-2.

They also found prior coronavirus infections can protect against subsequent infections with other coronavirus es.

Mice that had been immunised with COVID-19 vaccines and later were exposed to the common cold coronavirus (HCoV-OC43) were partially protected against the common cold, but the protection was much less robust, according to the study.

The reason, the scientists explained, is because both SARS-CoV-1 and SARS-CoV-2 are genetically similar — like cousins of one another — while the common cold coronavirus is more divergent from SARS-CoV-2.

“As long as the coronavirus is greater than 70 per cent related, the mice were protected,” Penaloza-MacMaster said.

“If they were exposed to a very different family of coronavirus es, the vaccines might confer less protection,” he said.

Given how different each coronavirus family is, the study authors said a universal coronavirus vaccine may not be possible.

However, there may be a path forward for developing a vaccine for each coronavirus family, they said.

“Our study helps us re-evaluate the concept of a universal coronavirus vaccine,” Penaloza-MacMaster said.

“It’s likely there isn’t one, but we might end up with a generic vaccine for each of the main families of coronavirus es,” he said.

For example, the scientist said, a universal Sarbecovirus vaccine can be made for SARS-CoV-1, SARS-CoV-2 and other SARS-related coronavirus es, and a universal Embecovirus for HCoV-OC43 and HKU1 that cause common colds.

In the study, Penaloza-MacMaster and Northwestern Medicine physician Igor Koralnik evaluated immune responses in humans who received SARS-CoV-2 vaccines, as well as in COVID-19 patients admitted to Northwestern Memorial Hospital.

“We found that these individuals developed antibody responses that neutralised a common cold coronavirus , HCoV-OC43,” Penaloza-MacMaster said.

“We are now measuring how long this cross-protection lasts,” he added.