We in the Northern Hemisphere know which strains of the virus to incorporate in the vaccine by the flu season happening in the Southern Hemisphere. The flu is a wintertime virus, so the virus circulating during the Northern Hemisphere outbreak informs the viruses in the vaccine for the Southern Hemisphere, and vice versa.
This year, due in part to COVID restrictions, and now lack thereof, the Southern Hemisphere experienced a much earlier and more severe season than previous years. We believe we may experience something similar here.
The flu dropped off dramatically in 2020 when we all went into isolation and heavily masked when we did go out. Flu and COVID are transmitted the same way, so avoidance of one led to avoidance of the other. We also had large outbreaks of COVID over the last two winters that kept people home. Now, as restrictions or mitigation efforts are reduced, people haven’t seen flu in the last few years, which means their odds of getting infected are substantially greater.
This is a huge concern. This could be a particularly rough winter for individuals getting the flu and having severe complications.
People with preexisting conditions that make them more susceptible to complications, such as cardiovascular diseases, lung diseases, asthma, are at a higher risk of having more severe infection. Elderly people are at increased risk of severe disease, as they generate poorer immune responses. Infants and toddlers may have more severe infections if they contract the flu since it may be their first exposure to the disease.
It really restricted the amount the virus spread. When you reduce the amount the virus spreads, the less likely it is to mutate. This reduced the population of influenza viruses that exists in the world and actually may have made predicting the strains to include in the influenza vaccine easier.
The surge was relatively small, but I think what that indicates to me is that we’re in for a rocky flu season this winter. It’s likely going to start early and last longer.
The media is calling it a “twindemic.” What’s going to end up happening is this could put a massive strain on our healthcare system. As the number of infections go up for flu, we could experience a similar wave of COVID again this winter, and our healthcare system could be further strained by an influx of flu and COVID cases.
You’ll generate a response against both viruses just as well as if you were to receive them individually. If you are at the pharmacy getting your COVID booster, you should absolutely get your flu shot at the same visit.
The more a population vaccinates, the more they’re immune to strains, and the more effective the vaccine is. However, most people do not receive the vaccine, and the largest populations that do, such as the elderly, are those that are least likely to generate a protective response. In addition, previous immunity can shape how you respond to the virus, and vaccines have been very effective against components of infection. Preexisting immunity also shapes which strains are dominant, which dictates how vaccines work against strains.
Overall, I highly recommend people get the flu vaccine sooner rather than later. As evidenced in the Southern Hemisphere, the winter flu season may start earlier than normal and may be worse than anything we’ve seen in years.
December 5, 2023