Why getting a flu shot is a good idea in countries heading into winter

As the southern hemisphere moves closer to winter, virologists are concerned about the upcoming influenza season. This may result in more people needing medical care for flu—including hospitalization—while the health system is still battling the coronavirus. This may swing the pendulum in favor of SARS-CoV-2 by making it harder to control the pandemic, especially in Africa, which has recorded the lowest number of cases thus far.

There are many other respiratory viruses that circulate throughout the year. But the influenza virus can be deadly. Influenza epidemics occur in late autumn and winter—between May and August—in the southern hemisphere and during the rainy season, which may be year round in the tropics.

Most people who get influenza only have a mild illness: a fever, cough (usually dry), headache, muscle and joint pain, severe malaise (feeling unwell), sore throat and a runny nose. But influenza can also cause more severe illness. This includes lower respiratory tract diseases that cause difficulty breathing, such as bronchitis or pneumonia. These conditions may require hospitalization or even be fatal.

These signs are very similar to those caused by COVID-19. It may create additional anxiety for patients and stress on the healthcare system this year. This is why it's advisable that everybody get the influenza vaccine. It will not protect people from COVID-19, but it will reduce influenza-related illness and in effect ease stress on health services during this pandemic.

COVID-19 and influenza

People older than 65 are most at risk and could die of either flu or COVID-19. Influenza also causes severe disease in young children. This is different to COVID-19, which has so far caused very few fatalities in children under nine. Pregnant women and people with HIV or other immune suppressive conditions are at high risk for severe disease and even death due to influenza. People with underlying health conditions may also experience COVID-19 more severely.

It would appear that COVID-19 has a higher fatality rate (1%-5%) than influenza (less than 0.5%). But during winter influenza can infect up to a third of the population. Every year seasonal influenza kills between 100,000 and 600,000 people worldwide. There are around 11,500 deaths in South Africa alone.

So why should the annual influenza season concern us at a time when COVID-19 appears to be much worse than flu?

Well, firstly we want to avoid visits to doctors if possible during the pandemic. This will reduce the stress on the healthcare system and help patients to avoid exposure to COVID-19 infected patients, so as to avoid the risk of having influenza and COVID-19 co-infections. Little information is available on the severity of COVID-19 and other viral co-infections. But a recent report suggests that influenza and COVID-19 co-infections may result in more severe disease in high-risk patients and complicate the diagnoses.

This further emphasizes the importance of getting the influenza vaccine. The pneumococcus vaccine can also reduce the number of bacterial secondary infections that can compound disease, especially in children and the elderly.

So who should get the vaccine?

The World Health Organisation (WHO) recommends annual vaccination for high-risk population groups. These include pregnant women, children aged between six months and five years, people older than 65 years, those with chronic medical conditions such as HIV, heart or lung problems, and healthcare workers.

Most countries provide vaccines for free to these high risk groups. But people of all ages will benefit from getting the flu vaccine. High-risk people should however be prioritized if the vaccine stocks run low.

There are, however, myths and questions about the flu vaccine that influence people's decisions about whether to get the vaccine. These must be addressed.

• How do I know the influenza vaccine matches the strains circulating during our season? There are three influenza subtypes that circulate globally at the same time that are included in the flu vaccine. Every year the WHO's global network of National Influenza Centres collaborate to identify the most common strains that are circulating in the northern and southern hemispheres. These strains are then used to produce specific vaccines for each hemisphere that are ready in time for the following year's influenza season. Influenza strains may mutate or drift genetically from year to year. But most of the time the strains in the vaccine are a very close match to the current circulating strains and provide protection against most if not all the strains in the vaccine.
• Can the influenza vaccine make you sick? No, the influenza vaccine only contains dead flu virus so it cannot give you flu. The flu vaccine is produced in eggs and killed to make the vaccine. Some people who are allergic to eggs may have a reaction to the egg proteins and shouldn't get the vaccine, but this is rare.
• Is it true that there is mercury in the vaccine that could be toxic? In the past, a preservative called Thimerosal was used in vaccines that contained trace amounts of ethyl-mercury. Etyl-mercury is not the same as methyl-mercury, which is found in certain fish and can be toxic if consumed at high levels. Nevertheless, due to public concerns Thimerosal was removed from all vaccines in 1999.
• I still got sick in the past after getting the flu vaccine. Other viruses such as rhinovirus or respiratory syncytial virus circulating at the same time as flu can also cause an infection with the same symptoms. The vaccine is about 50%-70% effective in preventing the flu. But if you do still get sick or if you get a co-infection with another virus, the flu vaccine will still reduce the severity of disease.

The flu vaccine will not protect you from getting COVID-19. But by being protected from influenza, people could avoid unnecessary doctors' visits and protect vulnerable groups from potentially more severe disease.