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Dr Rod Pearce
HEALTH
COVID-19 vaccines – will the immunity last? C
OVID-19 vaccines available in Australia are going to provide us with good protection. Overseas supply of the AstraZeneca (AZ) and Pfizer vaccines is limited but an Australian factory is making 1 million doses of AZ a week from late March 2021. Everyone in Australia will be able to get a vaccination over the next six months. After the first dose of any infection or vaccine, you will develop some immunity. Most times the body needs a reminder to develop long-term protection, and a second dose would normally be used to lock in that long-term immunity. What we don’t know is how long that immunity will last, and we don’t know how long natural immunity lasts. COVID-19 vaccines are some of the most studied vaccines ever produced. This is because of the number of people on whom we can test them. Other vaccines are developed at the same speed, but the testing process takes time because recruiting patients for trials normally takes years. The first two vaccines for COVID-19 used in Australia have: • Had the proper research done on development. • Been tested on small numbers of healthy volunteers and then tested on healthy patients. • Had double-blind placebo-controlled trials. Double-blind means the person administering the vaccine doesn’t know what he or she is giving (trial vaccine, placebo or another vaccine) and the recipient doesn’t know what he or she is receiving.
We might need yearly vaccinations for a few years until we all have immunity, and the strains get under control.
Anything that goes wrong in the next few weeks is recorded to see if there are more things happening to those getting the vaccine than those getting saline. These are known as adverse events following immunization (AEFI) and are closely followed in Australia and around the world. An example is someone having a car accident the day after an immunization. If it appeared that a vaccine was causing drowsiness, it might be that it was causing accidents. If a signal occurs during a trial, the trial is stopped, the “blind” injection is decoded and, if it is found that all the accidents occurred in the placebo group, the trial will continue. This happened with the AZ vaccine when a case of transverse myelitis (spinal cord problem and paralysis) halted the trial temporarily. But a review did not indicate that the vaccine had caused the problem. Post-vaccination deaths reported in Norway in January were related to pre-existing illness and poor health and clotting and bleeding concerns have been shown to be coincidental to the time the vaccine(s) were given. It has taken a while to work out how far apart the vaccine doses need to be to get maximum effect. The Pfizer vaccine is achieving good results with doses three weeks apart. We get the same benefit from the AZ vaccine if the doses are 12 weeks apart. In the real world (real-world evidence – RWE) both the vaccines available in Australia are showing they can reduce
the severity of disease, reduce deaths and reduce transmission (both around 80 per cent). We have not done routine testing and trials with pregnant women or children. About 20,000 women who had a COVID-19 vaccine found out later they were pregnant. There has been no problem, and pregnant women can have the vaccine if they want to after discussing it with their doctors. AZ has been tested on 18-year-olds and older. Pfizer is registered in Australia for 16 and older and we are waiting for specific testing on children before recommending vaccination. About a third of people will have side effects from the vaccine, usually a sore arm. Some people get an immune reaction looking like a red arm with an infection. Tiredness seems to happen as the immune system kicks in, slightly worse with the second injection. It is important to report all side effects and anything that happens after the vaccination so we can monitor AEFI to see if: • Thousands of other people are getting the same problem. • The effects are the same as predicted in the trial(s). • There is something new happening with the Australian vaccine (AZ). At this stage, the AZ and Pfizer vaccines will stop any spread in Australia. There is not enough of the “variant mutation” strains to cause problems here and shutting down any disease means less mutations and less risk. We might need yearly vaccinations for a few years until we all have immunity, and the strains get under control. It is expected that in about three to four years it will be less severe as a combination of natural immunity and vaccines make it a disease with which we can all live.
April 2021
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