COVID-19 vaccination may actually improve the efficacy of certain cancer treatments, despite initial concerns, a new study suggests. The unexpected finding, that patients with nasopharyngeal cancer respond better to treatment after vaccination with SinoVac, may help put to bed fears that COVID-19 vaccines interfere with cancer treatment and reduce its effectiveness.

Nasopharyngeal cancer – a type of cancer that affects the part of the throat running between the back of the nose and the back of the mouth – is commonly treated with drugs that activate the immune system. Specifically, they block a protein on the surface of immune cells called PD-1 receptors. With PD-1 blocked, unfavorable interactions that are often exploited by cancers are prevented, and an immune cell’s ability to target tumors is unleashed. 

Vaccination against COVID also targets this same immune response, which has sparked some concern among experts that the interplay between the two might affect patient outcomes.

"It was feared that the vaccine would not be compatible with anti-PD-1 therapy," explained Dr Jian Li of the University of Bonn in a statement. "This risk is especially true for nasopharyngeal cancer, which, like the SARS CoV-2 virus, affects the upper respiratory tract."

But, in the new study, on which Li is a co-author, these doubts were mitigated: instead of minimizing the effects of treatment, SinoVac – the Chinese COVID vaccine – seemed to enhance it.

The researchers recruited 1,537 people with nasopharyngeal cancer from 23 hospitals across China. Of these, 373 were vaccinated with SinoVac.

"Surprisingly, they responded significantly better to anti-PD-1 therapy than the unvaccinated patients," Professor Christian Kurts, also at the University of Bonn, said. "Furthermore, they did not experience severe side effects more often."

While the researchers cannot say for sure why this might be the case, they do offer some suggestions:

"We assume that vaccination activates certain immune cells, which then attack the tumor," offered Professor Qi Mei of Shanxi University Hospital. "We will now investigate this hypothesis further."

Summing up their findings, the authors write that the association they’ve identified between COVID-19 vaccination and improved nasopharyngeal cancer treatment is “interesting”, but acknowledge that it “needs to be validated in a larger cohort study”. It remains to be seen whether the association holds true for other COVID vaccines or cancer types.

Nasopharyngeal cancer is widespread in Southeast Asia and southern China, where it is suspected that air pollution may play a part in its prevalence. It has also previously been linked to diet and the Epstein-Barr virus. In Taiwan, it is now one of the leading causes of death among young men. 

Earlier this year, nasopharyngeal cancer was revealed as the likely cause of death of the world’s first pregnant ancient Egyptian mummy.

The study is published in the Annals of Oncology.