28 things your doctor wishes you knew about vaccines

Some people believe that certain batches of vaccines – known as “hot lots” – are responsible for more side effects than normal batches of vaccines. There was a suggestion that certain lots were linked with more fever than others in the 1990s, says Dr Edwards. But since then, “there doesn’t seem to have been any particular association.” Adverse events and possible side effects are reported to the CDC after every vaccine in introduced, but this doesn’t mean that the virus caused them, the WHO points out. And because lots vary in size from a few hundred thousand to several millions, it’s like comparing apples to oranges. Larger lots will be associated with more adverse effects because more people get them.

The WHO assures people that combo vaccines as well as giving more than one vaccine at the same time for different diseases have no adverse health effects. The organisation notes that vaccines don’t burden a child’s immune system more than common illnesses like strep throat and upper respiratory infections. Even new foods introduce new bacteria into the body, says the WHO. There have been plenty of studies on the issue and none have found an increased risk of problems. Indeed, there are advantages to combining vaccines in one injection, namely fewer visits to the doctor and fewer jabs.

The human papillomavirus vaccine protects against the human papillomavirus (HPV). Some types of HPV can cause genital warts and others are the main cause of cervical and other cancers. (There are more than 100 types of HPV, some more dangerous than others.) Vaccines can protect against most of the cancer-causing HPV types. Some parents are resistant to the idea of their children getting the shots because they worry their kids will see it as permission to have sex – unprotected. Several studies have busted this myth, including one published in 2019. The researchers found no link between sexual behaviour and getting the HPV vaccine: Participants did not start having sex earlier because of the vaccine, nor did they take on more sexual partners. Kids are smarter than that, says Dr Schaffner. (The vaccine is recommended for adolescent boys and girls, and can be given as early as age nine, because it’s thought to be most effective if someone has not yet been exposed to HPV.)

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The HPV vaccine is not only for girls, confirms Dr Schaffner. “The vaccine was originally touted as preventing cancer of the cervix, and while that is wonderfully true, it also prevents head, neck and anal cancers,” which are not gender-specific, he says. The vaccine can also prevent vaginal cancer. In Australia, HPV vaccine is currently provided free to both boys and girls aged 12-13 years through the National Immunisation Program (NIP). The vaccine requires two doses, the second six months to a year after the first.

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The HPV vaccine was first recommended in 2006. In the decade after it was introduced, HPV infections dropped by 86 percent in females aged 14 to 19 and 71 percent among women in their early 20s. What’s more, fewer cases of genital warts and precancerous cervical lesions have been noted. Protection from the vaccine also seems to be long-lasting with studies so far going out to 10 years. Even with the vaccine, experts still recommend that women get screened for cervical cancer starting at age 21 until they’re 65. The vaccine is also safe, with few side effects noted even though 120 million doses have been given.

Some people believe that the immunity gained through getting a virus is better than a vaccination. “That’s a disturbing notion,” says Dr Schaffner, “and it must come from people who have had no exposure to diseases that can be prevented through vaccination. Their assumption must be that the disease is trivial.” Schaffner says that this dangerous idea has become more common because we have eliminated so many diseases with vaccines that people don’t have experience with how traumatic and fatal viruses can be. Even though immunity from a disease may be higher than a vaccine (in measles, it is 100 percent versus 98-99 percent, respectively), you still have to get the disease, says Dr Edwards. And that’s way worse than the vaccine.

Low-grade fever, headaches and muscle aches are common side effects of the influenza vaccine. But this vaccine cannot give you the actual flu, reassures the CDC. That’s because flu shots are made with inactivated (killed) viruses, says Dr Kuhn. “I hear some people say ‘I got the flu shot and I got the flu’ but the flu vaccine is by definition incapable of causing disease,” he adds. “It may be you didn’t get it in time or didn’t mount a good immune response.”

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It’s possible, though less likely, to still contract the flu despite getting the vaccine. Sometimes the actual bugs circulating are different from the ones scientists predicted and that are included in the annual vaccine. Other times, a person’s immune system simply did not respond to the vaccine as well as it should. Several factors can affect immune response to the annual shot, including genetic make-up, any pre-existing immunity and underlying health conditions, according to an article in Human Vaccines & Immunotherapeutics. Age is also a factor, with older people responding less well to standard-dose vaccines. Then there’s the vaccination itself, which varies in effectiveness from year to year. On the other hand, we know that even if you do get sick, it should be less severe, says Dr Edwards. Flu shots can reduce hospitalisations and deaths, even if they don’t prevent every symptom.

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It’s true that children ages 6 months to 4 years, people 65 or older, pregnant women and anyone with a disease that compromises their immune system should definitely get a flu shot. But just because you don’t fall into one of those categories doesn’t mean you should skip vaccination. Flu shots are now recommended for everyone 6 months or older, every year, except in certain rare cases. “Herd immunity is an important concept,” says Dr Schaffner. “A vaccine not only protects the person vaccinated, but it also protects the community.” That includes those who can’t get flu shots, including babies under six months of age and those with severe, life threatening allergies to vaccine components.

Although there have been reports that the flu vaccine might increase a person’s risk of contracting other respiratory illnesses, this is not the case. “The current flu vaccine is an inactivated influenza virus that is incapable of causing any flu-like disease since there is no live virus involved,” says Dr Kuhn. Of course, plenty of other viruses are circulating at the same time as the flu so you do have a chance of contracting other illnesses, just not because of the flu vaccine.