Francisco R. Velázquez: After two light years, the 2022-2023 flu season may bring more sickness

By Francisco R. Velázquez, M.D., S.M., FCAP

Influenza is a viral infection that targets the respiratory system, nose, throat and lungs. It is commonly referred to as the “flu,” though it’s an entirely different entity than the stomach flu. The respiratory type spreads from person to person through sneezes, coughs or talking, which releases virus-containing respiratory droplets into the air. There is some data that suggests you may also get the flu by touching a contaminated surface and then touching your mouth, nose and, possibly, your eyes.

There are four types of influenza viruses: A, B, C and D. Influenza A viruses can be found in many animals including mammals, birds and humans. These are characterized by specific surface proteins which are used to further divide into several subtypes. Examples are H1N1 and H3N2. Type B can only infect humans and is usually characterized based on where it was originally identified. Some of the known lineages are B/Yamagata and B/Victoria. Influenza C can infect humans but typically causes mild illness and has not been associated with flu epidemics. The last type, D, usually affects cattle and is not known to affect humans.

More than 60 flu viruses have been identified. The predominance of one or more strains changes from year to year and is a key factor in the development of vaccines each year. Close to 144 influenza centers in more than 100 countries around the world collect data on circulating flu viruses, such as which strains are more common, the severity of disease, how fast the current strains are spreading, and historical effectiveness of vaccines with specific strains. These centers are part of the World Health Organization Global Influenza Surveillance and Response System. The information collected is sent to five WHO Collaborating Centers for Influenza. One of these is the Centers for Disease Control and Prevention in Atlanta. The best flu vaccine composition for the upcoming season in the United States is then determined by the Food and Drug Administration.

In the Northern Hemisphere the flu season usually starts in October, peaks in December and can last through May. In the Southern Hemisphere the usual flu season is April through October. This year, several countries, such as Australia, reported an early start and significant increases in flu activity, returning to pre-pandemic level case counts. This is compared to relatively mild flu seasons for the past couple of years.

There are several possible reasons for this trend. More than likely the ongoing COVID-19 pandemic with the precautionary, risk-mitigation strategies around it worked well for other respiratory viruses such as the flu. Many mitigation measures were discontinued as winter arrived in countries such as South Africa and Australia, allowing for more circulation of respiratory viruses in the population – a population with limited exposure to flu for the previous two years and no exposure at all for many young children.

In the 10 years prior to the pandemic, the U.S. saw millions of cases, generating hundreds of thousands of medical visits, tens of thousands of hospitalizations and several thousand deaths. In the 2020-21 season, we saw only a few thousand reported cases, though an increase in the tally of flu cases is expected in the final reports for the 2021-22 season which just ended. Looking ahead at the 2022-23 season, experts are once again expecting a significant number of flu cases. That’s because in the U.S. we have a similar situation to countries in the Southern Hemisphere, where masking and other mitigation efforts have decreased and access to activities has increased.

Although the flu does have seasonal predictability, the outcomes from the Southern Hemisphere are not guaranteed to reproduce in the Northern Hemisphere. Nonetheless it is worth noting the similarities in COVID-19 policies and guidance and the timing of decreased precautions. The flu is still the second most common cause of vaccine-preventable disease mortality, just behind COVID-19. Children tend to have a high incidence of infection, although the highest risk for severe disease, hospitalization and mortality remains with those over 65, children under 5, pregnant women and people with pre-existing conditions.

The good news is flu vaccines are widely available in the community and typically do a good job in preventing the more serious manifestations and complications of the disease. It is worth mentioning that flu vaccines and COVID-19 vaccines and boosters work very well but do not offer cross protection. Ideally, if you are eligible and your provider recommends it, you should get a flu and a COVID-19 vaccine/booster. You can get the two shots at the same time if clinically indicated. It’s generally recommended to get the flu shot before the end of October.

And if a fall gathering is in your future, don’t forget to get the shots at least two weeks prior. If we get vaccinated and boosted, we will have the greatest level of protection against two distinctive respiratory viruses that will co-exist this fall and winter.

Francisco R. Velázquez, M.D., S.M., FCAP is the health officer at Spokane Regional Health District.