COVID-19 Vaccine: Needles to the rescue?

Uptake, logistics and targeting will determine if the vaccine can allow life to return to normal. We built an interactive tool that can help explore the key factors standing between us and vaccine success for all regions in the UK.

by Kieran Dale, Christian Moroy and George Batchelor

Last week brought the encouraging news of Pfizer’s effective vaccine that could prevent more than 95% of people from getting COVID-19. This was accompanied by Oxford/AstraZeneca’s announcement that their vaccine is up to 90% effective, though their trials are still ongoing.

The end of the pandemic seems to be in sight. While this is undoubtedly very positive news, many hurdles remain before ending the pandemic is a reality.

There are still many unsolved problems. The necessary regulatory approval that the vaccines are safe to distribute is ongoing. Logistically, producing and transporting vaccines at scale is also a huge challenge. For example Pfizer’s MRNA vaccine typically needs to be stored at -70C, and two doses are required within a strict timeframe).

Efforts are being made to ensure worldwide equitable access to the vaccine, which range in price from Oxford’s (£2.23) to Pfizer’s (£29.47). There are concerns that mutations of the virus could undermine the vaccine effort. In all cases, vaccinating the vulnerable should be the priority, though decisions are yet to be finalised on who should receive the vaccine first.

Supposing all these problems are overcome, the only question that we need to answer is: would I take the vaccine?

How likely are people to take the vaccine?

First impressions might tell you that vaccine uptake on the whole would be very high, and any limitation on distributing the vaccine would be due to availability. The surveys show a range of different results, and depend on the country. A study of 20,000 adults from 27 countries showed an expected vaccine uptake of 74%, though this ranged from 97% in China to 54% in Russia.

Here in Great Britain, one survey of almost 1,600 people showed the difference in expected uptake varies considerably between age groups. Only half of surveyed people from 18-24 years of age were more likely than not to take the vaccine, while for people 65+, this figure was 82%.

How many people need to be vaccinated?

While a vaccine would primarily stop vulnerable people from getting ill and dying, there are also effects such as reducing the adverse effects of COVID and lockdown on other population health needs such as cancer. Critically, it also helps create “herd immunity” and slows the spread of the virus.

With an effective vaccine, creating herd immunity in the general population will be the goal. At 90% effectiveness and assuming a reproduction number of 2.5 (how readily the virus spreads), herd immunity can be achieved once 66% of the population is immune from vaccination or having caught the disease – this will reduce R below 1, and the virus will effectively die out.

The size of the population that needs to be vaccinated is larger if the effectiveness is lower or effective R higher. For example, if efficacy is less than the stated 90% (e.g. 80%) and R higher (e.g. 3) then up to 83% of the population would need the vaccine (less as some will have immunity from having caught the disease already) – see chart below.

Other measures to stop the spread would likely remain

However, a vaccine would likely not be the sole intervention to “flatten the curve”. Other measures would still be in place to reduce the reproduction number, such as wearing masks on public transport. One study showed that if a vaccine was the sole intervention, a vaccine with an efficacy of 80% would require at least 75% coverage (R_0 = 3.5) to put a halt to the pandemic. This would likely be lower if people remained socially distant and adhered to government guidance.

Major vaccine trials have set the goal of eradicating any symptomatic COVID-19 of any severity. The objectives of these trials are not reductions in hospital admissions, admissions to intensive care or death. Their main goal is stopping the spread of the virus, which studies show may be most effective if the vaccine is distributed to high-transmission, low-risk age groups (people under the age of 30 for example). This is dependent on how available the vaccine is, which if scarce should still be allocated to the most vulnerable such as those in care homes and care home workers. Whatever the approach, the general consensus is that vaccinating the elderly first then moving onto other, healthier groups of the population is the wisest option.

Saving lives should be the priority. We have seen evidence from other countries that only those countries that have successfully protected lives also managed to protect the economy. This means that other measures of stopping the spread in the community are still important while the vaccine is being rolled out.

Consequences of low uptake

There are serious consequences for low uptake. These can be broken into three broad categories.

1. Risk-to-life – Low vaccine uptake will increase the reproduction number of COVID, spreading the disease to vulnerable people. Care homes in particular have been at-risk throughout the pandemic, and ensuring high uptake among frail and elderly people will reduce unnecessary loss of life.

The shielded population (people aged 85 and above) and vulnerable population (people aged 66-84) are defined very generally. This provides an overview of the worst affected areas for loss-of-life due to older age profiles. Using a simple case fatality ratio of 2% for the shielded population, 1% for the vulnerable population and 0.1% for the working population, we can define the risk to loss-of-life compared to a baseline (no intervention). Full restrictions put in place will half loss-of-life risk.

2. Risk to the economy – the working age population that is still at-risk can cause a burden on the economy. Not reaching “herd immunity” could result in further measures that would harm businesses, such as curfews and local lockdowns. This will be affected by the size of the working population, uptake, vaccine effectiveness and restrictions.

The equation for this is the proportion of the working population still at-risk of COVID, multiplied by a scaling factor representing restrictions (50% to 150% of risk value)

3. Risk of a third wave – we are currently undergoing a second wave. As the pandemic progresses, fatigue can set in and compliance to government measures can drop. Whether this lockdown will be as effective as the previous one is unknown, although more lockdowns seem unlikely. Studies have shown that decreased perceived effectiveness of lockdown measures was linked to non-adherence. The second wave coincided with worsening weather in the UK. Will this be as much of an issue as we head into warmer months?

Risk of a third wave will also incorporate “high-spreaders” (defined as those aged 6-17). Schools and universities are remaining open, and younger demographics have the potential to spread the virus widely. If herd immunity is reached (the proportion of the population that needs to be vaccinated to beat the virus), there is no risk of a third wave. If this threshold isn’t reached, the risk factor is the proportion of the population that still needs to be vaccinated compared to a baseline of no vaccinations.

Vaccine uptake ideal and worst-case scenarios

Our interactive vaccine impact exploration tool shows which areas of England are affected most :

https://edgehealth.shinyapps.io/Vaccine_Efficacy/

Three scenarios can be explored in the tool: ideal, expected and worst-case. These outline proportions of population cohorts who are vaccinated, and show risk factors at local authority level for each of the aforementioned risk categories.

As the analysis is based on age profiles at local authority level, it visualises the following outcomes:

· Restrictions reduce risk to loss-of-life but increase risk to the economy.

· The most at-risk areas for loss-of-life will be those with a higher proportion of older people

· Third wave likelihood is highly dependent on the uptake in working population and high-transmission population.

· Herd immunity is reached much more easily with the introduction of an effective vaccine.

Conclusion

Work needs to commence on the logistics of vaccinating the population. This will be the next big challenge, and is key to building public trust that the pandemic can be beaten. Ensuring all the systems are in place to be able to roll-out the vaccination effectively and at-scale is key.

The big obstacles include: sufficient uptake across the population (especially super spreaders!). Super spreader vaccination is key to flatten the curve but only when combined with priority access for at-risk population cohorts efficient distribution that involves the primary care system and strict compliance to vaccine dose schedules.

Enabling success across all of these dimensions is key to save lives, reduce pandemic-induced strain on the economy and remove the threat of a third wave.