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Bringing it forward

August 27, 2021 - 09:11 -- Admin

As I have related here, I had my first AstraZeneca vaccination at lunchtime on the last day of June and was due to get the second dose the requisite 12 weeks later (i.e. September 22)1. However, as things have become more desperate in New South Wales and that has overflowed into the Australian Capital Territory, it has been suggested by the Australian Technical Advisory Group on Immunisation (ATAGI) for people in areas where there are outbreaks, that they should bring forward their second dose of AstraZeneca. ATAGI has also urged younger people who are unable to get access to the Pfizer vaccine because of its limited supply, to consider getting the AstraZeneca vaccine2. The AstraZeneca vaccine (two doses) has been shown to lead to a 60-67% reduction in the likelihood of symptomatic disease and a 92% decrease in the likelihood of hospitalisation3.

Most of the side effects of the AstraZeneca vaccine were much as I had after my first dose, just a feeling of tiredness and mild illness1. However, in rare cases there are severe side effects. These can include anaphylaxis3, the possibility of which is the reason I had to hang around in the doctors’ surgery for 15 minutes after my first dose1. The other side effect is perhaps the more dangerous TTS, which is shorthand for thrombosis with thrombocytopenia syndrome3.  

TTS involves blood clots (thrombosis) and low levels of blood platelets (thrombocytopenia), In Australia symptoms of TTS have occurred between 4 and 42 days after the first dose of the AstraZeneca vaccine. The blood clots can occur in various parts of the body, and can lead to death. The mechanism that causes TTS is not fully understood, but fortunately, TTS is very rare and only averages 1.4 cases per 100,000 in my age group (60-69). The risk increases as you get older (it is 1.9 per 100,000 for those over 80), but the risk is greatest for those under 50 where it reaches 3.1 cases per 100,0004.

The reason the AstraZeneca vaccine was not suggested by ATAGI for younger people was because their risk of dying from Covid-19 is very low, especially where the number of cases is low. The increased risk of TTS for younger people in this situation essentially makes the risk of death from the vaccine more likely than from the disease. However, in the middle of a large wave of infection, such as that in Sydney, the risk from the disease is greater.

Bringing your second dose forward has given rise to some concern that this will lessen protection against the virus. The efficacy of the vaccine against symptomatic disease ranges from about 62% to 73%, with the higher efficacy seen after a longer 12-week interval between doses. However, the efficacy is still fairly good when a second dose is given even as early as three weeks after the first dose, at about 60%, according to ATAGI5.

Given that the ACT is in lockdown and there are cases (fortunately not the huge numbers of Sydney) cropping up every day, I decided to bring forward my second AstraZeneca dose, and have booked in for September 1st. This is 9 weeks after my first dose, rather than the 12 weeks initially recommended. I just rang the doctors’ surgery and asked them if I could change my appointment, and there was no problem in doing so.

Professor Adrian Esterman, chair of Biostatistics at the University of South Australia, has said “When you look at the vial with AstraZeneca in it, it says to give the second dose from between four to twelve weeks” and, “If you have both shots, whether at eight or twelve weeks, or whether you are fully vaccinated with AstraZeneca or Pfizer, you are pretty much covered against severe disease and death”5. Sign me up.

Sources

  1. https://blotreport.com/2021/07/04/one-down-one-to-go/
  2. https://www.abc.net.au/news/2021-07-13/astrazeneca-covid-19-atagi-advice-sydney-outbreak-second-dose/100286392
  3. https://theconversation.com/over-18-and-considering-astrazeneca-this-may-help-you-decide-165085
  4. https://www.health.gov.au/initiatives-and-programs/covid-19-vaccines/learn-about-covid-19-vaccines/about-the-astrazeneca-vaxzevria-covid-19-vaccine
  5. https://www.theguardian.com/society/2021/jul/09/should-you-bring-forward-your-second-dose-of-astrazeneca-to-protect-against-the-delta-variant