Why you should not miss the next flu vaccination season
Experts were expecting the flu (influenza) season to be quite problematic, especially in the Northern Hemisphere. But that was not the case. The measures to prevent the spread of COVID-19 — e.g., suspension of international travel, physical distancing, use of masks — also helped prevent the flu.
Dr. Rachel Baker from Princeton University commented that there was a clear decrease in flu cases when the lockdowns were announced. This finding was further exemplified by what happened in Hawaii, which usually has persistent cases throughout the year. While some researchers estimate that measures against COVID-19 have led to a 20% drop in the transmission of influenza and other respiratory diseases, a Hong Kong study showed a 44% decline in flu transmission after the introduction of these measures. “This is one of the clear signs that these interventions work”, added Dr. Baker. These measures are really effective in stopping the spread of viruses. Dr. Baker commented that the situation is remarkably different this year, with virtually no flu cases in the Northern Hemisphere during the winter of 2020 (full commentary here).
Dr. Ian Barr from the Peter Doherty Institute added that there was also no flu season in the Southern Hemisphere. This was also commented on by American health experts, such as Dr. Anthony Fauci from the U.S. National Institute of Allergy and Infectious Disease (NIAID). Australia and other Southern Hemisphere nations had easy flu seasons (the flu season there runs from March to August) apparently thanks to preventive measures against the coronavirus.
There could be other factors in the reduction of cases though. Dr. John McCauley from the Francis Crick Institute believes that part of the sudden decrease could be due to health officials being focused on COVID-19 and essentially not testing for influenza. In addition, the US Centers for Disease Control and Prevention (CDC) reported that more Americans chose to receive the flu vaccine during the last season than during the previous year.
Nonetheless, health experts in the United States had pointed out that the country could experience an easy flu season since measures against COVID-19 would also help prevent the spread of the flu. Reports from these experts now confirm that in fact the numbers were extremely low for cases of the flu and other common respiratory and gastrointestinal viruses.
The Washington Post cites data from the CDC clinical laboratory network: in the third week of December 2019, 16,2% of nearly 30,000 samples tested for influenza A were positive. During the same period in 2020, only 0.3% tested positive.
Why are these findings important?
Choosing which influenza strains to include in the next vaccination round has been difficult. Researchers who contribute to the global plan for the annual influenza vaccine indicate that there is a dearth of information about which strains are circulating in the population. But they are working on finding these data. All in all, more samples were tested in 2020 than in the previous year, but there was very little of the flu virus to be found. There were minimal outbreaks in Bangladesh, India, Southeast Asia, Western Africa, and Europe.
Here’s the dilemma for the team from the World Health Organization (WHO):
- Should the same strains of the last developed vaccine be maintained?; or
- Should it be assumed that the strains in circulation before the pandemic will be those that will return next season? Or will there be circulation of those strains that have now, even in small numbers, circulated around the world?
Researchers would obviously prefer to have more data to guide them in this difficult decision. Apparently, three of the four strains that will be present in the next vaccine should be the same as those already present in the last developed vaccine. The Influenza A H3 strain which was recently found in circulation is expected to be incorporated into the next vaccine as well.
No one should miss the coming vaccination season for influenza
Researchers suggest that as the population’s immunity decreases over this “lost flu season”, large outbreaks may become more likely when life returns to normal and public health measures implemented during the pandemic are relaxed. Experts are predicting substantial outbreaks of viruses in general, with a peak next winter in the Northern Hemisphere. For influenza the complete picture is complicated, since we must consider the transmissibility and evolutionary dynamics of the strains circulating alongside the effect of the vaccines. But a similar result is possible.
The potential good news is that, with fewer infections, the flu virus did not have as many opportunities to mutate and evolve. This could mean the strains that will emerge in the near future could be similar to those already circulating before the pandemic, making current vaccines still effective.
In addition, Dr. McCauley commented that viruses should start with a very low presence and then they may not have time to spread to large number of people during seasonal window. Other researchers have added that they believe it will probably take several years for the flu numbers to return to “normal levels”.
Despite these possibilities, Dr. McCauley cautions that “we have to plan for a worse season”. Effective vaccines can help protect against a major flu outbreak. This is especially important at a time when the COVID-19 pandemic is not completely controlled because “the two together, influenza and COVID-19, would be very difficult to control”, added Dr. McCauley.
News coming from Australia should be a warning sign. COVID-19 has a very low presence in the country, but in recent months the flu has returned. Influenza cases among children aged 5 years and under have increased sixfold by December, when these cases are generally lower.
How the influenza season will play out is still unknown. We must all track the start of the influenza vaccination season and ensure that we are all protected.
References:
- With No Flu Season, Next Year’s Vaccine Prep is Tricky — Medscape, March 03, 2021
- Washington Post — “Coronavirus shutdowns have quashed nearly all other common viruses. But scientists say a rebound is coming.” https://www.washingtonpost.com/health/2021/01/12/covid-shutdowns-viruses/
- COVID Protections Suppressed Flu Season in US — Medscape — Jan 13, 20
