The Pfizer vaccine's efficacy seems too good to be true – but in fact, the truth may be better still.
The Pfizer Covid-19 vaccine is potentially part of a revolution in vaccinology. The key ingredient, mRNA, is notoriously unstable, but scientists worked out a way to make it stable enough to be suitable for vaccination.
It works by persuading the human body to develop an immune response to the key target protein of SARS-COV-2, the virus that causes Covid-19. The immune response that is elicited is multi-component, effectively foiling the virus’ attempts to invade, and provides protection that may last for years.
Randomised clinical trials have revealed that the Pfizer vaccine has remarkably high efficacy – vaccinated humans have 95 percent protection against developing symptomatic disease when exposed to the virus. Further results suggest vaccinated individuals also have over 90 percent protection against developing asymptomatic infection. Furthermore, contacts of ‘breakthrough cases’ in vaccinated individuals have been shown to be much less likely to become infected than contacts of unvaccinated cases. Is this too good to be true? Actually, the truth may be even better.
When we try to understand how effective a vaccine is, the results from randomised ‘efficacy’ trials and from specific circumstances are only part of the story. For example, efficacy trials involve a relatively small number of individuals recruited in the context of high numbers of cases in the population. The ‘herd’ or ‘indirect’ effects from vaccinated people on the (vastly bigger) remainder of the population are negligible and not measured. Also, study participants can often be quite a select group, who may be more or less likely to benefit from vaccine than the rest of the population.
In contrast, when vaccines are rolled out, the population may have fewer or no cases of Covid-19 at the time, almost everyone is targeted for vaccination, and all the indirect effects from large numbers of vaccinated people on those who are not vaccinated come into play. A key issue is that no one knows exactly how effective the vaccine will be when rolled out in the general population. It might be better or worse than expected. Modelling can only take you so far.
We in New Zealand benefitted early in the pandemic from being able to learn from what was happening in other countries, applying things that had been successful and avoiding things that were not. A similar opportunity has presented itself to us now, as we look towards re-opening to the rest of the world. On January 27, Israel reached nearly 12,000 cases in a day at the height of a devastating wave of Covid-19 in a population of nine million people.
Many of these cases were due to the ‘Alpha’ variant, which had first been identified in the United Kingdom. Vaccination with the Pfizer vaccine commenced in mid-December 2020. Israel has now vaccinated around 80 percent of its population over 16 years of age, with almost 60 percent of the total population having now received two doses. Soon children over the age of 12 will receive the vaccine. As shown in the figure from Johns Hopkins University, the results have been remarkable. From the peak in January, cases have plummeted to a seven-day average of 16 cases per day, despite progressive lifting of public health restrictions to near pre-pandemic levels. Israel is heading for elimination of community transmission.
Epidemiologists from Israel have started to comment on what they have learned from the remarkable success of the Pfizer vaccine in their population. In an interview in the Times of Israel Professors Nadav Davidovitch and Ronit Calderon-Margalit identified five key lessons they feel are relevant.
Firstly, consistent with data from elsewhere, they found that children are not a big virus vector and school closures should be kept to a minimum. This is consistent with the success of vaccination when rolled out in Israel even though it has been restricted to adults so far. The second lesson is that vaccines are effective, even in countries where cases are ‘sky-high’. So there is always hope. The third is that strict border controls are important while vaccination is being rolled out, due to the potential dangers from new variants.
The fourth lesson is that ‘green passes’ - certificates given to people who are vaccinated - were highly effective in a high caseload situation in helping the country progressively open up. And the fifth lesson is that the game is not over. This is because there are continued challenges of ‘long Covid’ in those who were infected and there are mental health effects from the stress of the pandemic, not least among health professionals who continue to be needed in the health system.
Perhaps a sixth lesson is being ignored. While it is of great benefit to countries who can vaccinate their populations to do so, the global pandemic requires a global health approach.
Countries like Israel and New Zealand ignore their near or far neighbours at their peril. The virus is able to mutate and its ability to evolve to evade vaccine protection is yet to be fully understood. So, while we can be excited about the fact that our Government has secured for us what looks to be a truly outstanding vaccine, we need to be intentionally and proactively part of the global fight. We can even send our vaccinated, and often more than willing, health professionals into the middle of the storm.
