Dealing with the Respiratory Viruses that Cause Covid-19 or Flu

Influenza and COVID-19: what are they in common?

Currently, the two most important respiratory viruses the healthcare authority is paying attention to are SARS-COV-2 (causing COVID-19) and influenza A and B viruses (Flu A and B). The Flu A and B viruses (named by the core protein types) are the major flu viruses. Flu A virus is the cause of the annual flu epidemic, whereas Flu B virus outbreaks occur every 2 to 4 years.

What is in common between these two types of viruses? First, they are the only two types of viruses that have led to the five pandemics in the past century. The flu viruses caused the first 4 pandemics in 1918 (H1N1), 1957 (H2N2), 1968 (H3N2), and 2009-2010 (4 strains including H1N1), and SARS-COV-2 resulted in the current pandemic started in 2019 and have created six waves of spreads through different variants. Secondly, both types of viruses induce similar symptoms in the human body, such as dry cough, headache, fever, and fatigue. However, COVID-19 may also have the symptoms of loss of taste and smell and shortness of breath. These symptoms are quite different from a common cold, with symptoms of sneezing, running or stuffy nose, and sore throat.

Coinfection by COVID-19 and Flu viruses

These viruses not only cause similar symptoms by infecting people separately, but they can also infect the same person during the same period (coinfection). Since Flu viruses have a short incubation and shedding period compared to SARS-COV-2, the flu viruses may not be detected when COVID-19 is detected in a coinfected person.

You may be very curious about the severity of the syndromes in a coinfected person compared with a person who is infected by only one type of virus. Due to the limited studies, the reported results are not consistent or even contradictory. Animal studies have indicated that coinfection causes severe weight loss and lung damage due to inflammation. A recent study shows that coinfected patients have more severe syndrome. In addition, a study by Public Health England has found that the risk of death in coinfected patients is about 2 times higher than that for patients with COVID-19 alone. These findings make testing both Flu A&B and SARS-COV-2 simultaneously important for the appropriate therapies for severe cases.

Testing of both COVID-19 and Flu A and B viruses

In the 2019-2020 winter, the flu cases have significantly fallen due to the policies and actions to prevent the spread of COVID-19. Even with a low number of cases of Flu virus infection, a low coinfection rate (0.7% in one case and 1.3% in another study of the total COVID-19 cases) is still detected. With the COVID-19 policy loosened up, the Flu viruses may come back strongly this winter. The good news is that the testing kits for the detection of both types of viruses together are available now.

Both rapid antigen testing kits and gold-standard qPCR kits are commonly used for testing. The antigen test does not need special equipment and can be easily used at home, schools, and workplaces. These kits are especially beneficial and accurate for the detection of people who have shown symptoms. However, for asymptomatic people, these rapid kits may not be sensitive enough, producing false-negative results. In these cases, the qPCR method or other nucleic-acid-based methods should kick in to confirm. For accuracy, the qPCR method should be always used if time and condition allow.

DiaCarta COVID-19 and Flu A&B combo test

DiaCarta has developed the qPCR-based COVID-19 and Flu A&B combo test kit using nasopharyngeal samples. The kit has achieved the CE mark and is in the process of FDA EUA application. The healthcare providers that recognize CE-IVD can use these kits for testing. In the US, CLIA labs can validate the test in their own lab for testing (under regulation by the State of New York, only FDA EUA test kits are allowed for testing). This highly sensitive kit (detecting three viruses from 100 to 300 copies per ml sample) shows high clinical sensitivity and specificity on three validated qPCR instruments.

Vaccination to prevent COVID-19 and Flu A and B

Although therapy is always a good choice once an infection occurs, it is more important to prevent the infection if we can. Both flu vaccines and COVID-19 vaccines are available separately to prepare for the flu season, which comes in October and peaks between next January to February. It is always a good idea to get vaccinated ahead of time.

Finally, it is also good to know that the combined vaccine against both flu and covid-19 is on the way. Once available, you only need one shot to get immunity to both types of viruses.

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