COVID is surging in the world's most vaccinated country. Why?

C Raina MacIntyre, UNSW


Around 71 per cent of people have had at least one dose of a COVID vaccine, and 62 per cent have been fully vaccinated. Of these, 57 per cent have received the Sinopharm vaccine, and 43 per cent AstraZeneca.

Despite this, there has been a recent surge in cases, with 37 per cent of new active cases and 20 per cent of hospital cases being fully vaccinated. The country has had to reimpose some restrictions.

How can this be happening? There are several possible explanations:

  1. the herd immunity threshold has not been reached – 62 per cent vaccination is likely not adequate with the vaccines being used


  3. variants that escape vaccine protection are dominant in Seychelles




Let’s break this down.

Variants can escape vaccine protection


In South Africa, one study showed AstraZeneca has 0-10 per cent efficacy against this variant, prompting the South African government to stop using that vaccine in February.




Israel, where the UK variant was dominant, also has a very high vaccination rate, having vaccinated nearly 60 per cent of its population with Pfizer. It found 92 per cent effectiveness against any infection including asymptomatic infection, and Israel has seen a large drop in new cases.

The United Kingdom has used a combination of Pfizer and AstraZeneca vaccines. More than 50 per cent of the population have had a single dose and almost 30 per cent are fully vaccinated. The country has also seen a significant decline in case numbers.

But there’s a current surge of cases in north-west England, with most new cases in the city of Bolton being the Indian variant. This variant is also causing outbreaks in Singapore, which had previously controlled the virus well.



We need to use high-efficacy vaccines to achieve herd immunity

The reported efficacy of Sinopharm is 79 per cent and AstraZeneca is 62-70 per cent from phase 3 clinical trials.

Our research at the Kirby Institute showed that, in New South Wales, using a vaccine with 90 per cent efficacy against all infection means herd immunity could be achieved if 66 per cent of the population was vaccinated.

However, using lower efficacy vaccines means more people need to be vaccinated. If the vaccine is 60 per cent effective, the proportion needing to be vaccinated rises to 100 per cent.

When you get an efficacy of less than 60 per cent, herd immunity is not achievable.


But the B117 variant is 43-90 per cent more contagious than D614G, so the R0 may be up to 4.75. This will require higher vaccination rates to control spread.

What’s more, the Indian variant B1617 has been estimated to be at least 50 per cent more contagious than B117, which could take the R0 to over 7, and takes us into uncharted territory.



A UK modelling study found using very low efficacy vaccines would result in the economy barely breaking even over 10 years because it would fail to control transmission. On the other hand, using very high efficacy vaccines would result in much better economic outcomes.

Vaccinating the world is the only way to end the pandemic




The Conversation

Are you one of the Australians hesitating to get a COVID vaccine? Or have you been first in the queue for an available vaccine?




Written by The Conversation