Protective essential oil attenuates influenza virus infection: an in vitro study in MDCK cells.
Abstract
BACKGROUND:

Influenza is a significant cause of morbidity and mortality. The recent pandemic of a novel H1N1 influenza virus has stressed the importance of the search for effective treatments for this disease. Essential oils from aromatic plants have been used for a wide variety of applications, such as personal hygiene, therapeutic massage and even medical practice. In this paper, we investigate the potential role of an essential oil in antiviral activity.
CONCLUSIONS:

An essential oil blend significantly attenuates influenza virus PR8 infectivity in vitro without affecting viral binding or cellular internalization in MDCK cells. Oil treated virus continued to express viral mRNAs but had minimal expression of viral proteins, suggesting that the antiviral effect may be due to inhibition of viral protein translation.

https://www.ncbi.nlm.nih.gov/pubmed/21078173
What essential oils are good for the flu?

https://www.medicalnewstoday.com/articles/321401#essential-oils

Researchers are exploring both the effectiveness of essential oils for flu treatment and the best ways to apply these oils.

Research has found that the following essential oils have significant anti-influenza virus properties:

Bergamot oil is effective against flu viruses as a vapor after just 10 minutes of exposure.
Eucalyptus oil shows anti-viral activity as a vapor.
Red thyme oil is effective against flu viruses as a liquid phase.
Cinnamon leaf oil also shows antiviral activity as a liquid.
Tea tree oil is effective against the flu virus within 5 to 10 minutes of exposure, as found in another study.
Lemon balm is also shown to prevent the avian influenza (bird flu) virus from reproducing.

Researchers have found that a commercial blend of essential oils significantly reduced the influenza virus’ ability to spread.

This product, sold as doTERRA On Guard, contains essential oils of wild orange peel, clove bud, cinnamon leaf, cinnamon bark, eucalyptus leaves, and rosemary.